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-rw-r--r--tools/objtool/check.c2281
1 files changed, 2281 insertions, 0 deletions
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
new file mode 100644
index 000000000..c0ab27368
--- /dev/null
+++ b/tools/objtool/check.c
@@ -0,0 +1,2281 @@
+/*
+ * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <string.h>
+#include <stdlib.h>
+
+#include "builtin.h"
+#include "check.h"
+#include "elf.h"
+#include "special.h"
+#include "arch.h"
+#include "warn.h"
+
+#include <linux/hashtable.h>
+#include <linux/kernel.h>
+
+#define FAKE_JUMP_OFFSET -1
+
+struct alternative {
+ struct list_head list;
+ struct instruction *insn;
+};
+
+const char *objname;
+struct cfi_state initial_func_cfi;
+
+struct instruction *find_insn(struct objtool_file *file,
+ struct section *sec, unsigned long offset)
+{
+ struct instruction *insn;
+
+ hash_for_each_possible(file->insn_hash, insn, hash, offset)
+ if (insn->sec == sec && insn->offset == offset)
+ return insn;
+
+ return NULL;
+}
+
+static struct instruction *next_insn_same_sec(struct objtool_file *file,
+ struct instruction *insn)
+{
+ struct instruction *next = list_next_entry(insn, list);
+
+ if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
+ return NULL;
+
+ return next;
+}
+
+static struct instruction *next_insn_same_func(struct objtool_file *file,
+ struct instruction *insn)
+{
+ struct instruction *next = list_next_entry(insn, list);
+ struct symbol *func = insn->func;
+
+ if (!func)
+ return NULL;
+
+ if (&next->list != &file->insn_list && next->func == func)
+ return next;
+
+ /* Check if we're already in the subfunction: */
+ if (func == func->cfunc)
+ return NULL;
+
+ /* Move to the subfunction: */
+ return find_insn(file, func->cfunc->sec, func->cfunc->offset);
+}
+
+#define func_for_each_insn_all(file, func, insn) \
+ for (insn = find_insn(file, func->sec, func->offset); \
+ insn; \
+ insn = next_insn_same_func(file, insn))
+
+#define func_for_each_insn(file, func, insn) \
+ for (insn = find_insn(file, func->sec, func->offset); \
+ insn && &insn->list != &file->insn_list && \
+ insn->sec == func->sec && \
+ insn->offset < func->offset + func->len; \
+ insn = list_next_entry(insn, list))
+
+#define func_for_each_insn_continue_reverse(file, func, insn) \
+ for (insn = list_prev_entry(insn, list); \
+ &insn->list != &file->insn_list && \
+ insn->sec == func->sec && insn->offset >= func->offset; \
+ insn = list_prev_entry(insn, list))
+
+#define sec_for_each_insn_from(file, insn) \
+ for (; insn; insn = next_insn_same_sec(file, insn))
+
+#define sec_for_each_insn_continue(file, insn) \
+ for (insn = next_insn_same_sec(file, insn); insn; \
+ insn = next_insn_same_sec(file, insn))
+
+/*
+ * Check if the function has been manually whitelisted with the
+ * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
+ * due to its use of a context switching instruction.
+ */
+static bool ignore_func(struct objtool_file *file, struct symbol *func)
+{
+ struct rela *rela;
+
+ /* check for STACK_FRAME_NON_STANDARD */
+ if (file->whitelist && file->whitelist->rela)
+ list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
+ if (rela->sym->type == STT_SECTION &&
+ rela->sym->sec == func->sec &&
+ rela->addend == func->offset)
+ return true;
+ if (rela->sym->type == STT_FUNC && rela->sym == func)
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * This checks to see if the given function is a "noreturn" function.
+ *
+ * For global functions which are outside the scope of this object file, we
+ * have to keep a manual list of them.
+ *
+ * For local functions, we have to detect them manually by simply looking for
+ * the lack of a return instruction.
+ *
+ * Returns:
+ * -1: error
+ * 0: no dead end
+ * 1: dead end
+ */
+static int __dead_end_function(struct objtool_file *file, struct symbol *func,
+ int recursion)
+{
+ int i;
+ struct instruction *insn;
+ bool empty = true;
+
+ /*
+ * Unfortunately these have to be hard coded because the noreturn
+ * attribute isn't provided in ELF data.
+ */
+ static const char * const global_noreturns[] = {
+ "__stack_chk_fail",
+ "panic",
+ "do_exit",
+ "do_task_dead",
+ "__module_put_and_exit",
+ "complete_and_exit",
+ "kvm_spurious_fault",
+ "__reiserfs_panic",
+ "lbug_with_loc",
+ "fortify_panic",
+ "usercopy_abort",
+ "machine_real_restart",
+ "rewind_stack_do_exit",
+ };
+
+ if (func->bind == STB_WEAK)
+ return 0;
+
+ if (func->bind == STB_GLOBAL)
+ for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
+ if (!strcmp(func->name, global_noreturns[i]))
+ return 1;
+
+ if (!func->len)
+ return 0;
+
+ insn = find_insn(file, func->sec, func->offset);
+ if (!insn->func)
+ return 0;
+
+ func_for_each_insn_all(file, func, insn) {
+ empty = false;
+
+ if (insn->type == INSN_RETURN)
+ return 0;
+ }
+
+ if (empty)
+ return 0;
+
+ /*
+ * A function can have a sibling call instead of a return. In that
+ * case, the function's dead-end status depends on whether the target
+ * of the sibling call returns.
+ */
+ func_for_each_insn_all(file, func, insn) {
+ if (insn->type == INSN_JUMP_UNCONDITIONAL) {
+ struct instruction *dest = insn->jump_dest;
+
+ if (!dest)
+ /* sibling call to another file */
+ return 0;
+
+ if (dest->func && dest->func->pfunc != insn->func->pfunc) {
+
+ /* local sibling call */
+ if (recursion == 5) {
+ /*
+ * Infinite recursion: two functions
+ * have sibling calls to each other.
+ * This is a very rare case. It means
+ * they aren't dead ends.
+ */
+ return 0;
+ }
+
+ return __dead_end_function(file, dest->func,
+ recursion + 1);
+ }
+ }
+
+ if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
+ /* sibling call */
+ return 0;
+ }
+
+ return 1;
+}
+
+static int dead_end_function(struct objtool_file *file, struct symbol *func)
+{
+ return __dead_end_function(file, func, 0);
+}
+
+static void clear_insn_state(struct insn_state *state)
+{
+ int i;
+
+ memset(state, 0, sizeof(*state));
+ state->cfa.base = CFI_UNDEFINED;
+ for (i = 0; i < CFI_NUM_REGS; i++) {
+ state->regs[i].base = CFI_UNDEFINED;
+ state->vals[i].base = CFI_UNDEFINED;
+ }
+ state->drap_reg = CFI_UNDEFINED;
+ state->drap_offset = -1;
+}
+
+/*
+ * Call the arch-specific instruction decoder for all the instructions and add
+ * them to the global instruction list.
+ */
+static int decode_instructions(struct objtool_file *file)
+{
+ struct section *sec;
+ struct symbol *func;
+ unsigned long offset;
+ struct instruction *insn;
+ int ret;
+
+ for_each_sec(file, sec) {
+
+ if (!(sec->sh.sh_flags & SHF_EXECINSTR))
+ continue;
+
+ if (strcmp(sec->name, ".altinstr_replacement") &&
+ strcmp(sec->name, ".altinstr_aux") &&
+ strncmp(sec->name, ".discard.", 9))
+ sec->text = true;
+
+ for (offset = 0; offset < sec->len; offset += insn->len) {
+ insn = malloc(sizeof(*insn));
+ if (!insn) {
+ WARN("malloc failed");
+ return -1;
+ }
+ memset(insn, 0, sizeof(*insn));
+ INIT_LIST_HEAD(&insn->alts);
+ clear_insn_state(&insn->state);
+
+ insn->sec = sec;
+ insn->offset = offset;
+
+ ret = arch_decode_instruction(file->elf, sec, offset,
+ sec->len - offset,
+ &insn->len, &insn->type,
+ &insn->immediate,
+ &insn->stack_op);
+ if (ret)
+ goto err;
+
+ if (!insn->type || insn->type > INSN_LAST) {
+ WARN_FUNC("invalid instruction type %d",
+ insn->sec, insn->offset, insn->type);
+ ret = -1;
+ goto err;
+ }
+
+ hash_add(file->insn_hash, &insn->hash, insn->offset);
+ list_add_tail(&insn->list, &file->insn_list);
+ }
+
+ list_for_each_entry(func, &sec->symbol_list, list) {
+ if (func->type != STT_FUNC)
+ continue;
+
+ if (!find_insn(file, sec, func->offset)) {
+ WARN("%s(): can't find starting instruction",
+ func->name);
+ return -1;
+ }
+
+ func_for_each_insn(file, func, insn)
+ if (!insn->func)
+ insn->func = func;
+ }
+ }
+
+ return 0;
+
+err:
+ free(insn);
+ return ret;
+}
+
+/*
+ * Mark "ud2" instructions and manually annotated dead ends.
+ */
+static int add_dead_ends(struct objtool_file *file)
+{
+ struct section *sec;
+ struct rela *rela;
+ struct instruction *insn;
+ bool found;
+
+ /*
+ * By default, "ud2" is a dead end unless otherwise annotated, because
+ * GCC 7 inserts it for certain divide-by-zero cases.
+ */
+ for_each_insn(file, insn)
+ if (insn->type == INSN_BUG)
+ insn->dead_end = true;
+
+ /*
+ * Check for manually annotated dead ends.
+ */
+ sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
+ if (!sec)
+ goto reachable;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s", sec->name);
+ return -1;
+ }
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (insn)
+ insn = list_prev_entry(insn, list);
+ else if (rela->addend == rela->sym->sec->len) {
+ found = false;
+ list_for_each_entry_reverse(insn, &file->insn_list, list) {
+ if (insn->sec == rela->sym->sec) {
+ found = true;
+ break;
+ }
+ }
+
+ if (!found) {
+ WARN("can't find unreachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+ } else {
+ WARN("can't find unreachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+
+ insn->dead_end = true;
+ }
+
+reachable:
+ /*
+ * These manually annotated reachable checks are needed for GCC 4.4,
+ * where the Linux unreachable() macro isn't supported. In that case
+ * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
+ * not a dead end.
+ */
+ sec = find_section_by_name(file->elf, ".rela.discard.reachable");
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s", sec->name);
+ return -1;
+ }
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (insn)
+ insn = list_prev_entry(insn, list);
+ else if (rela->addend == rela->sym->sec->len) {
+ found = false;
+ list_for_each_entry_reverse(insn, &file->insn_list, list) {
+ if (insn->sec == rela->sym->sec) {
+ found = true;
+ break;
+ }
+ }
+
+ if (!found) {
+ WARN("can't find reachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+ } else {
+ WARN("can't find reachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+
+ insn->dead_end = false;
+ }
+
+ return 0;
+}
+
+/*
+ * Warnings shouldn't be reported for ignored functions.
+ */
+static void add_ignores(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct section *sec;
+ struct symbol *func;
+
+ for_each_sec(file, sec) {
+ list_for_each_entry(func, &sec->symbol_list, list) {
+ if (func->type != STT_FUNC)
+ continue;
+
+ if (!ignore_func(file, func))
+ continue;
+
+ func_for_each_insn_all(file, func, insn)
+ insn->ignore = true;
+ }
+ }
+}
+
+/*
+ * FIXME: For now, just ignore any alternatives which add retpolines. This is
+ * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
+ * But it at least allows objtool to understand the control flow *around* the
+ * retpoline.
+ */
+static int add_nospec_ignores(struct objtool_file *file)
+{
+ struct section *sec;
+ struct rela *rela;
+ struct instruction *insn;
+
+ sec = find_section_by_name(file->elf, ".rela.discard.nospec");
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s", sec->name);
+ return -1;
+ }
+
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!insn) {
+ WARN("bad .discard.nospec entry");
+ return -1;
+ }
+
+ insn->ignore_alts = true;
+ }
+
+ return 0;
+}
+
+/*
+ * Find the destination instructions for all jumps.
+ */
+static int add_jump_destinations(struct objtool_file *file)
+{
+ struct instruction *insn;
+ struct rela *rela;
+ struct section *dest_sec;
+ unsigned long dest_off;
+
+ for_each_insn(file, insn) {
+ if (insn->type != INSN_JUMP_CONDITIONAL &&
+ insn->type != INSN_JUMP_UNCONDITIONAL)
+ continue;
+
+ if (insn->offset == FAKE_JUMP_OFFSET)
+ continue;
+
+ rela = find_rela_by_dest_range(insn->sec, insn->offset,
+ insn->len);
+ if (!rela) {
+ dest_sec = insn->sec;
+ dest_off = insn->offset + insn->len + insn->immediate;
+ } else if (rela->sym->type == STT_SECTION) {
+ dest_sec = rela->sym->sec;
+ dest_off = rela->addend + 4;
+ } else if (rela->sym->sec->idx) {
+ dest_sec = rela->sym->sec;
+ dest_off = rela->sym->sym.st_value + rela->addend + 4;
+ } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
+ /*
+ * Retpoline jumps are really dynamic jumps in
+ * disguise, so convert them accordingly.
+ */
+ insn->type = INSN_JUMP_DYNAMIC;
+ insn->retpoline_safe = true;
+ continue;
+ } else {
+ /* sibling call */
+ insn->jump_dest = 0;
+ continue;
+ }
+
+ insn->jump_dest = find_insn(file, dest_sec, dest_off);
+ if (!insn->jump_dest) {
+
+ /*
+ * This is a special case where an alt instruction
+ * jumps past the end of the section. These are
+ * handled later in handle_group_alt().
+ */
+ if (!strcmp(insn->sec->name, ".altinstr_replacement"))
+ continue;
+
+ WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
+ insn->sec, insn->offset, dest_sec->name,
+ dest_off);
+ return -1;
+ }
+
+ /*
+ * For GCC 8+, create parent/child links for any cold
+ * subfunctions. This is _mostly_ redundant with a similar
+ * initialization in read_symbols().
+ *
+ * If a function has aliases, we want the *first* such function
+ * in the symbol table to be the subfunction's parent. In that
+ * case we overwrite the initialization done in read_symbols().
+ *
+ * However this code can't completely replace the
+ * read_symbols() code because this doesn't detect the case
+ * where the parent function's only reference to a subfunction
+ * is through a switch table.
+ */
+ if (insn->func && insn->jump_dest->func &&
+ insn->func != insn->jump_dest->func &&
+ !strstr(insn->func->name, ".cold.") &&
+ strstr(insn->jump_dest->func->name, ".cold.")) {
+ insn->func->cfunc = insn->jump_dest->func;
+ insn->jump_dest->func->pfunc = insn->func;
+ }
+ }
+
+ return 0;
+}
+
+/*
+ * Find the destination instructions for all calls.
+ */
+static int add_call_destinations(struct objtool_file *file)
+{
+ struct instruction *insn;
+ unsigned long dest_off;
+ struct rela *rela;
+
+ for_each_insn(file, insn) {
+ if (insn->type != INSN_CALL)
+ continue;
+
+ rela = find_rela_by_dest_range(insn->sec, insn->offset,
+ insn->len);
+ if (!rela) {
+ dest_off = insn->offset + insn->len + insn->immediate;
+ insn->call_dest = find_symbol_by_offset(insn->sec,
+ dest_off);
+
+ if (!insn->call_dest && !insn->ignore) {
+ WARN_FUNC("unsupported intra-function call",
+ insn->sec, insn->offset);
+ if (retpoline)
+ WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
+ return -1;
+ }
+
+ } else if (rela->sym->type == STT_SECTION) {
+ insn->call_dest = find_symbol_by_offset(rela->sym->sec,
+ rela->addend+4);
+ if (!insn->call_dest ||
+ insn->call_dest->type != STT_FUNC) {
+ WARN_FUNC("can't find call dest symbol at %s+0x%x",
+ insn->sec, insn->offset,
+ rela->sym->sec->name,
+ rela->addend + 4);
+ return -1;
+ }
+ } else
+ insn->call_dest = rela->sym;
+ }
+
+ return 0;
+}
+
+/*
+ * The .alternatives section requires some extra special care, over and above
+ * what other special sections require:
+ *
+ * 1. Because alternatives are patched in-place, we need to insert a fake jump
+ * instruction at the end so that validate_branch() skips all the original
+ * replaced instructions when validating the new instruction path.
+ *
+ * 2. An added wrinkle is that the new instruction length might be zero. In
+ * that case the old instructions are replaced with noops. We simulate that
+ * by creating a fake jump as the only new instruction.
+ *
+ * 3. In some cases, the alternative section includes an instruction which
+ * conditionally jumps to the _end_ of the entry. We have to modify these
+ * jumps' destinations to point back to .text rather than the end of the
+ * entry in .altinstr_replacement.
+ *
+ * 4. It has been requested that we don't validate the !POPCNT feature path
+ * which is a "very very small percentage of machines".
+ */
+static int handle_group_alt(struct objtool_file *file,
+ struct special_alt *special_alt,
+ struct instruction *orig_insn,
+ struct instruction **new_insn)
+{
+ struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
+ unsigned long dest_off;
+
+ last_orig_insn = NULL;
+ insn = orig_insn;
+ sec_for_each_insn_from(file, insn) {
+ if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
+ break;
+
+ if (special_alt->skip_orig)
+ insn->type = INSN_NOP;
+
+ insn->alt_group = true;
+ last_orig_insn = insn;
+ }
+
+ if (next_insn_same_sec(file, last_orig_insn)) {
+ fake_jump = malloc(sizeof(*fake_jump));
+ if (!fake_jump) {
+ WARN("malloc failed");
+ return -1;
+ }
+ memset(fake_jump, 0, sizeof(*fake_jump));
+ INIT_LIST_HEAD(&fake_jump->alts);
+ clear_insn_state(&fake_jump->state);
+
+ fake_jump->sec = special_alt->new_sec;
+ fake_jump->offset = FAKE_JUMP_OFFSET;
+ fake_jump->type = INSN_JUMP_UNCONDITIONAL;
+ fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
+ fake_jump->func = orig_insn->func;
+ }
+
+ if (!special_alt->new_len) {
+ if (!fake_jump) {
+ WARN("%s: empty alternative at end of section",
+ special_alt->orig_sec->name);
+ return -1;
+ }
+
+ *new_insn = fake_jump;
+ return 0;
+ }
+
+ last_new_insn = NULL;
+ insn = *new_insn;
+ sec_for_each_insn_from(file, insn) {
+ if (insn->offset >= special_alt->new_off + special_alt->new_len)
+ break;
+
+ last_new_insn = insn;
+
+ insn->ignore = orig_insn->ignore_alts;
+
+ if (insn->type != INSN_JUMP_CONDITIONAL &&
+ insn->type != INSN_JUMP_UNCONDITIONAL)
+ continue;
+
+ if (!insn->immediate)
+ continue;
+
+ dest_off = insn->offset + insn->len + insn->immediate;
+ if (dest_off == special_alt->new_off + special_alt->new_len) {
+ if (!fake_jump) {
+ WARN("%s: alternative jump to end of section",
+ special_alt->orig_sec->name);
+ return -1;
+ }
+ insn->jump_dest = fake_jump;
+ }
+
+ if (!insn->jump_dest) {
+ WARN_FUNC("can't find alternative jump destination",
+ insn->sec, insn->offset);
+ return -1;
+ }
+ }
+
+ if (!last_new_insn) {
+ WARN_FUNC("can't find last new alternative instruction",
+ special_alt->new_sec, special_alt->new_off);
+ return -1;
+ }
+
+ if (fake_jump)
+ list_add(&fake_jump->list, &last_new_insn->list);
+
+ return 0;
+}
+
+/*
+ * A jump table entry can either convert a nop to a jump or a jump to a nop.
+ * If the original instruction is a jump, make the alt entry an effective nop
+ * by just skipping the original instruction.
+ */
+static int handle_jump_alt(struct objtool_file *file,
+ struct special_alt *special_alt,
+ struct instruction *orig_insn,
+ struct instruction **new_insn)
+{
+ if (orig_insn->type == INSN_NOP)
+ return 0;
+
+ if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
+ WARN_FUNC("unsupported instruction at jump label",
+ orig_insn->sec, orig_insn->offset);
+ return -1;
+ }
+
+ *new_insn = list_next_entry(orig_insn, list);
+ return 0;
+}
+
+/*
+ * Read all the special sections which have alternate instructions which can be
+ * patched in or redirected to at runtime. Each instruction having alternate
+ * instruction(s) has them added to its insn->alts list, which will be
+ * traversed in validate_branch().
+ */
+static int add_special_section_alts(struct objtool_file *file)
+{
+ struct list_head special_alts;
+ struct instruction *orig_insn, *new_insn;
+ struct special_alt *special_alt, *tmp;
+ struct alternative *alt;
+ int ret;
+
+ ret = special_get_alts(file->elf, &special_alts);
+ if (ret)
+ return ret;
+
+ list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
+
+ orig_insn = find_insn(file, special_alt->orig_sec,
+ special_alt->orig_off);
+ if (!orig_insn) {
+ WARN_FUNC("special: can't find orig instruction",
+ special_alt->orig_sec, special_alt->orig_off);
+ ret = -1;
+ goto out;
+ }
+
+ new_insn = NULL;
+ if (!special_alt->group || special_alt->new_len) {
+ new_insn = find_insn(file, special_alt->new_sec,
+ special_alt->new_off);
+ if (!new_insn) {
+ WARN_FUNC("special: can't find new instruction",
+ special_alt->new_sec,
+ special_alt->new_off);
+ ret = -1;
+ goto out;
+ }
+ }
+
+ if (special_alt->group) {
+ if (!special_alt->orig_len) {
+ WARN_FUNC("empty alternative entry",
+ orig_insn->sec, orig_insn->offset);
+ continue;
+ }
+
+ ret = handle_group_alt(file, special_alt, orig_insn,
+ &new_insn);
+ if (ret)
+ goto out;
+ } else if (special_alt->jump_or_nop) {
+ ret = handle_jump_alt(file, special_alt, orig_insn,
+ &new_insn);
+ if (ret)
+ goto out;
+ }
+
+ alt = malloc(sizeof(*alt));
+ if (!alt) {
+ WARN("malloc failed");
+ ret = -1;
+ goto out;
+ }
+
+ alt->insn = new_insn;
+ list_add_tail(&alt->list, &orig_insn->alts);
+
+ list_del(&special_alt->list);
+ free(special_alt);
+ }
+
+out:
+ return ret;
+}
+
+static int add_switch_table(struct objtool_file *file, struct instruction *insn,
+ struct rela *table, struct rela *next_table)
+{
+ struct rela *rela = table;
+ struct instruction *alt_insn;
+ struct alternative *alt;
+ struct symbol *pfunc = insn->func->pfunc;
+ unsigned int prev_offset = 0;
+
+ list_for_each_entry_from(rela, &table->rela_sec->rela_list, list) {
+ if (rela == next_table)
+ break;
+
+ /* Make sure the switch table entries are consecutive: */
+ if (prev_offset && rela->offset != prev_offset + 8)
+ break;
+
+ /* Detect function pointers from contiguous objects: */
+ if (rela->sym->sec == pfunc->sec &&
+ rela->addend == pfunc->offset)
+ break;
+
+ alt_insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!alt_insn)
+ break;
+
+ /* Make sure the jmp dest is in the function or subfunction: */
+ if (alt_insn->func->pfunc != pfunc)
+ break;
+
+ alt = malloc(sizeof(*alt));
+ if (!alt) {
+ WARN("malloc failed");
+ return -1;
+ }
+
+ alt->insn = alt_insn;
+ list_add_tail(&alt->list, &insn->alts);
+ prev_offset = rela->offset;
+ }
+
+ if (!prev_offset) {
+ WARN_FUNC("can't find switch jump table",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ return 0;
+}
+
+/*
+ * find_switch_table() - Given a dynamic jump, find the switch jump table in
+ * .rodata associated with it.
+ *
+ * There are 3 basic patterns:
+ *
+ * 1. jmpq *[rodata addr](,%reg,8)
+ *
+ * This is the most common case by far. It jumps to an address in a simple
+ * jump table which is stored in .rodata.
+ *
+ * 2. jmpq *[rodata addr](%rip)
+ *
+ * This is caused by a rare GCC quirk, currently only seen in three driver
+ * functions in the kernel, only with certain obscure non-distro configs.
+ *
+ * As part of an optimization, GCC makes a copy of an existing switch jump
+ * table, modifies it, and then hard-codes the jump (albeit with an indirect
+ * jump) to use a single entry in the table. The rest of the jump table and
+ * some of its jump targets remain as dead code.
+ *
+ * In such a case we can just crudely ignore all unreachable instruction
+ * warnings for the entire object file. Ideally we would just ignore them
+ * for the function, but that would require redesigning the code quite a
+ * bit. And honestly that's just not worth doing: unreachable instruction
+ * warnings are of questionable value anyway, and this is such a rare issue.
+ *
+ * 3. mov [rodata addr],%reg1
+ * ... some instructions ...
+ * jmpq *(%reg1,%reg2,8)
+ *
+ * This is a fairly uncommon pattern which is new for GCC 6. As of this
+ * writing, there are 11 occurrences of it in the allmodconfig kernel.
+ *
+ * As of GCC 7 there are quite a few more of these and the 'in between' code
+ * is significant. Esp. with KASAN enabled some of the code between the mov
+ * and jmpq uses .rodata itself, which can confuse things.
+ *
+ * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
+ * ensure the same register is used in the mov and jump instructions.
+ *
+ * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
+ */
+static struct rela *find_switch_table(struct objtool_file *file,
+ struct symbol *func,
+ struct instruction *insn)
+{
+ struct rela *text_rela, *rodata_rela;
+ struct instruction *orig_insn = insn;
+ struct section *rodata_sec;
+ unsigned long table_offset;
+
+ /*
+ * Backward search using the @first_jump_src links, these help avoid
+ * much of the 'in between' code. Which avoids us getting confused by
+ * it.
+ */
+ for (;
+ &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
+ insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
+
+ if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
+ break;
+
+ /* allow small jumps within the range */
+ if (insn->type == INSN_JUMP_UNCONDITIONAL &&
+ insn->jump_dest &&
+ (insn->jump_dest->offset <= insn->offset ||
+ insn->jump_dest->offset > orig_insn->offset))
+ break;
+
+ /* look for a relocation which references .rodata */
+ text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
+ insn->len);
+ if (!text_rela || text_rela->sym->type != STT_SECTION ||
+ !text_rela->sym->sec->rodata)
+ continue;
+
+ table_offset = text_rela->addend;
+ rodata_sec = text_rela->sym->sec;
+
+ if (text_rela->type == R_X86_64_PC32)
+ table_offset += 4;
+
+ /*
+ * Make sure the .rodata address isn't associated with a
+ * symbol. gcc jump tables are anonymous data.
+ */
+ if (find_symbol_containing(rodata_sec, table_offset))
+ continue;
+
+ rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
+ if (rodata_rela) {
+ /*
+ * Use of RIP-relative switch jumps is quite rare, and
+ * indicates a rare GCC quirk/bug which can leave dead
+ * code behind.
+ */
+ if (text_rela->type == R_X86_64_PC32)
+ file->ignore_unreachables = true;
+
+ return rodata_rela;
+ }
+ }
+
+ return NULL;
+}
+
+
+static int add_func_switch_tables(struct objtool_file *file,
+ struct symbol *func)
+{
+ struct instruction *insn, *last = NULL, *prev_jump = NULL;
+ struct rela *rela, *prev_rela = NULL;
+ int ret;
+
+ func_for_each_insn_all(file, func, insn) {
+ if (!last)
+ last = insn;
+
+ /*
+ * Store back-pointers for unconditional forward jumps such
+ * that find_switch_table() can back-track using those and
+ * avoid some potentially confusing code.
+ */
+ if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
+ insn->offset > last->offset &&
+ insn->jump_dest->offset > insn->offset &&
+ !insn->jump_dest->first_jump_src) {
+
+ insn->jump_dest->first_jump_src = insn;
+ last = insn->jump_dest;
+ }
+
+ if (insn->type != INSN_JUMP_DYNAMIC)
+ continue;
+
+ rela = find_switch_table(file, func, insn);
+ if (!rela)
+ continue;
+
+ /*
+ * We found a switch table, but we don't know yet how big it
+ * is. Don't add it until we reach the end of the function or
+ * the beginning of another switch table in the same function.
+ */
+ if (prev_jump) {
+ ret = add_switch_table(file, prev_jump, prev_rela, rela);
+ if (ret)
+ return ret;
+ }
+
+ prev_jump = insn;
+ prev_rela = rela;
+ }
+
+ if (prev_jump) {
+ ret = add_switch_table(file, prev_jump, prev_rela, NULL);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+
+/*
+ * For some switch statements, gcc generates a jump table in the .rodata
+ * section which contains a list of addresses within the function to jump to.
+ * This finds these jump tables and adds them to the insn->alts lists.
+ */
+static int add_switch_table_alts(struct objtool_file *file)
+{
+ struct section *sec;
+ struct symbol *func;
+ int ret;
+
+ if (!file->rodata)
+ return 0;
+
+ for_each_sec(file, sec) {
+ list_for_each_entry(func, &sec->symbol_list, list) {
+ if (func->type != STT_FUNC)
+ continue;
+
+ ret = add_func_switch_tables(file, func);
+ if (ret)
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
+static int read_unwind_hints(struct objtool_file *file)
+{
+ struct section *sec, *relasec;
+ struct rela *rela;
+ struct unwind_hint *hint;
+ struct instruction *insn;
+ struct cfi_reg *cfa;
+ int i;
+
+ sec = find_section_by_name(file->elf, ".discard.unwind_hints");
+ if (!sec)
+ return 0;
+
+ relasec = sec->rela;
+ if (!relasec) {
+ WARN("missing .rela.discard.unwind_hints section");
+ return -1;
+ }
+
+ if (sec->len % sizeof(struct unwind_hint)) {
+ WARN("struct unwind_hint size mismatch");
+ return -1;
+ }
+
+ file->hints = true;
+
+ for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
+ hint = (struct unwind_hint *)sec->data->d_buf + i;
+
+ rela = find_rela_by_dest(sec, i * sizeof(*hint));
+ if (!rela) {
+ WARN("can't find rela for unwind_hints[%d]", i);
+ return -1;
+ }
+
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!insn) {
+ WARN("can't find insn for unwind_hints[%d]", i);
+ return -1;
+ }
+
+ cfa = &insn->state.cfa;
+
+ if (hint->type == UNWIND_HINT_TYPE_SAVE) {
+ insn->save = true;
+ continue;
+
+ } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
+ insn->restore = true;
+ insn->hint = true;
+ continue;
+ }
+
+ insn->hint = true;
+
+ switch (hint->sp_reg) {
+ case ORC_REG_UNDEFINED:
+ cfa->base = CFI_UNDEFINED;
+ break;
+ case ORC_REG_SP:
+ cfa->base = CFI_SP;
+ break;
+ case ORC_REG_BP:
+ cfa->base = CFI_BP;
+ break;
+ case ORC_REG_SP_INDIRECT:
+ cfa->base = CFI_SP_INDIRECT;
+ break;
+ case ORC_REG_R10:
+ cfa->base = CFI_R10;
+ break;
+ case ORC_REG_R13:
+ cfa->base = CFI_R13;
+ break;
+ case ORC_REG_DI:
+ cfa->base = CFI_DI;
+ break;
+ case ORC_REG_DX:
+ cfa->base = CFI_DX;
+ break;
+ default:
+ WARN_FUNC("unsupported unwind_hint sp base reg %d",
+ insn->sec, insn->offset, hint->sp_reg);
+ return -1;
+ }
+
+ cfa->offset = hint->sp_offset;
+ insn->state.type = hint->type;
+ insn->state.end = hint->end;
+ }
+
+ return 0;
+}
+
+static int read_retpoline_hints(struct objtool_file *file)
+{
+ struct section *sec;
+ struct instruction *insn;
+ struct rela *rela;
+
+ sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s", sec->name);
+ return -1;
+ }
+
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (!insn) {
+ WARN("bad .discard.retpoline_safe entry");
+ return -1;
+ }
+
+ if (insn->type != INSN_JUMP_DYNAMIC &&
+ insn->type != INSN_CALL_DYNAMIC) {
+ WARN_FUNC("retpoline_safe hint not an indirect jump/call",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ insn->retpoline_safe = true;
+ }
+
+ return 0;
+}
+
+static void mark_rodata(struct objtool_file *file)
+{
+ struct section *sec;
+ bool found = false;
+
+ /*
+ * This searches for the .rodata section or multiple .rodata.func_name
+ * sections if -fdata-sections is being used. The .str.1.1 and .str.1.8
+ * rodata sections are ignored as they don't contain jump tables.
+ */
+ for_each_sec(file, sec) {
+ if (!strncmp(sec->name, ".rodata", 7) &&
+ !strstr(sec->name, ".str1.")) {
+ sec->rodata = true;
+ found = true;
+ }
+ }
+
+ file->rodata = found;
+}
+
+static int decode_sections(struct objtool_file *file)
+{
+ int ret;
+
+ mark_rodata(file);
+
+ ret = decode_instructions(file);
+ if (ret)
+ return ret;
+
+ ret = add_dead_ends(file);
+ if (ret)
+ return ret;
+
+ add_ignores(file);
+
+ ret = add_nospec_ignores(file);
+ if (ret)
+ return ret;
+
+ ret = add_jump_destinations(file);
+ if (ret)
+ return ret;
+
+ ret = add_special_section_alts(file);
+ if (ret)
+ return ret;
+
+ ret = add_call_destinations(file);
+ if (ret)
+ return ret;
+
+ ret = add_switch_table_alts(file);
+ if (ret)
+ return ret;
+
+ ret = read_unwind_hints(file);
+ if (ret)
+ return ret;
+
+ ret = read_retpoline_hints(file);
+ if (ret)
+ return ret;
+
+ return 0;
+}
+
+static bool is_fentry_call(struct instruction *insn)
+{
+ if (insn->type == INSN_CALL &&
+ insn->call_dest->type == STT_NOTYPE &&
+ !strcmp(insn->call_dest->name, "__fentry__"))
+ return true;
+
+ return false;
+}
+
+static bool has_modified_stack_frame(struct insn_state *state)
+{
+ int i;
+
+ if (state->cfa.base != initial_func_cfi.cfa.base ||
+ state->cfa.offset != initial_func_cfi.cfa.offset ||
+ state->stack_size != initial_func_cfi.cfa.offset ||
+ state->drap)
+ return true;
+
+ for (i = 0; i < CFI_NUM_REGS; i++)
+ if (state->regs[i].base != initial_func_cfi.regs[i].base ||
+ state->regs[i].offset != initial_func_cfi.regs[i].offset)
+ return true;
+
+ return false;
+}
+
+static bool has_valid_stack_frame(struct insn_state *state)
+{
+ if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
+ state->regs[CFI_BP].offset == -16)
+ return true;
+
+ if (state->drap && state->regs[CFI_BP].base == CFI_BP)
+ return true;
+
+ return false;
+}
+
+static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
+{
+ struct cfi_reg *cfa = &state->cfa;
+ struct stack_op *op = &insn->stack_op;
+
+ if (cfa->base != CFI_SP && cfa->base != CFI_SP_INDIRECT)
+ return 0;
+
+ /* push */
+ if (op->dest.type == OP_DEST_PUSH)
+ cfa->offset += 8;
+
+ /* pop */
+ if (op->src.type == OP_SRC_POP)
+ cfa->offset -= 8;
+
+ /* add immediate to sp */
+ if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
+ op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
+ cfa->offset -= op->src.offset;
+
+ return 0;
+}
+
+static void save_reg(struct insn_state *state, unsigned char reg, int base,
+ int offset)
+{
+ if (arch_callee_saved_reg(reg) &&
+ state->regs[reg].base == CFI_UNDEFINED) {
+ state->regs[reg].base = base;
+ state->regs[reg].offset = offset;
+ }
+}
+
+static void restore_reg(struct insn_state *state, unsigned char reg)
+{
+ state->regs[reg].base = CFI_UNDEFINED;
+ state->regs[reg].offset = 0;
+}
+
+/*
+ * A note about DRAP stack alignment:
+ *
+ * GCC has the concept of a DRAP register, which is used to help keep track of
+ * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
+ * register. The typical DRAP pattern is:
+ *
+ * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
+ * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
+ * 41 ff 72 f8 pushq -0x8(%r10)
+ * 55 push %rbp
+ * 48 89 e5 mov %rsp,%rbp
+ * (more pushes)
+ * 41 52 push %r10
+ * ...
+ * 41 5a pop %r10
+ * (more pops)
+ * 5d pop %rbp
+ * 49 8d 62 f8 lea -0x8(%r10),%rsp
+ * c3 retq
+ *
+ * There are some variations in the epilogues, like:
+ *
+ * 5b pop %rbx
+ * 41 5a pop %r10
+ * 41 5c pop %r12
+ * 41 5d pop %r13
+ * 41 5e pop %r14
+ * c9 leaveq
+ * 49 8d 62 f8 lea -0x8(%r10),%rsp
+ * c3 retq
+ *
+ * and:
+ *
+ * 4c 8b 55 e8 mov -0x18(%rbp),%r10
+ * 48 8b 5d e0 mov -0x20(%rbp),%rbx
+ * 4c 8b 65 f0 mov -0x10(%rbp),%r12
+ * 4c 8b 6d f8 mov -0x8(%rbp),%r13
+ * c9 leaveq
+ * 49 8d 62 f8 lea -0x8(%r10),%rsp
+ * c3 retq
+ *
+ * Sometimes r13 is used as the DRAP register, in which case it's saved and
+ * restored beforehand:
+ *
+ * 41 55 push %r13
+ * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
+ * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
+ * ...
+ * 49 8d 65 f0 lea -0x10(%r13),%rsp
+ * 41 5d pop %r13
+ * c3 retq
+ */
+static int update_insn_state(struct instruction *insn, struct insn_state *state)
+{
+ struct stack_op *op = &insn->stack_op;
+ struct cfi_reg *cfa = &state->cfa;
+ struct cfi_reg *regs = state->regs;
+
+ /* stack operations don't make sense with an undefined CFA */
+ if (cfa->base == CFI_UNDEFINED) {
+ if (insn->func) {
+ WARN_FUNC("undefined stack state", insn->sec, insn->offset);
+ return -1;
+ }
+ return 0;
+ }
+
+ if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
+ return update_insn_state_regs(insn, state);
+
+ switch (op->dest.type) {
+
+ case OP_DEST_REG:
+ switch (op->src.type) {
+
+ case OP_SRC_REG:
+ if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
+ cfa->base == CFI_SP &&
+ regs[CFI_BP].base == CFI_CFA &&
+ regs[CFI_BP].offset == -cfa->offset) {
+
+ /* mov %rsp, %rbp */
+ cfa->base = op->dest.reg;
+ state->bp_scratch = false;
+ }
+
+ else if (op->src.reg == CFI_SP &&
+ op->dest.reg == CFI_BP && state->drap) {
+
+ /* drap: mov %rsp, %rbp */
+ regs[CFI_BP].base = CFI_BP;
+ regs[CFI_BP].offset = -state->stack_size;
+ state->bp_scratch = false;
+ }
+
+ else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
+
+ /*
+ * mov %rsp, %reg
+ *
+ * This is needed for the rare case where GCC
+ * does:
+ *
+ * mov %rsp, %rax
+ * ...
+ * mov %rax, %rsp
+ */
+ state->vals[op->dest.reg].base = CFI_CFA;
+ state->vals[op->dest.reg].offset = -state->stack_size;
+ }
+
+ else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
+ cfa->base == CFI_BP) {
+
+ /*
+ * mov %rbp, %rsp
+ *
+ * Restore the original stack pointer (Clang).
+ */
+ state->stack_size = -state->regs[CFI_BP].offset;
+ }
+
+ else if (op->dest.reg == cfa->base) {
+
+ /* mov %reg, %rsp */
+ if (cfa->base == CFI_SP &&
+ state->vals[op->src.reg].base == CFI_CFA) {
+
+ /*
+ * This is needed for the rare case
+ * where GCC does something dumb like:
+ *
+ * lea 0x8(%rsp), %rcx
+ * ...
+ * mov %rcx, %rsp
+ */
+ cfa->offset = -state->vals[op->src.reg].offset;
+ state->stack_size = cfa->offset;
+
+ } else {
+ cfa->base = CFI_UNDEFINED;
+ cfa->offset = 0;
+ }
+ }
+
+ break;
+
+ case OP_SRC_ADD:
+ if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
+
+ /* add imm, %rsp */
+ state->stack_size -= op->src.offset;
+ if (cfa->base == CFI_SP)
+ cfa->offset -= op->src.offset;
+ break;
+ }
+
+ if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
+
+ /* lea disp(%rbp), %rsp */
+ state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
+ break;
+ }
+
+ if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
+
+ /* drap: lea disp(%rsp), %drap */
+ state->drap_reg = op->dest.reg;
+
+ /*
+ * lea disp(%rsp), %reg
+ *
+ * This is needed for the rare case where GCC
+ * does something dumb like:
+ *
+ * lea 0x8(%rsp), %rcx
+ * ...
+ * mov %rcx, %rsp
+ */
+ state->vals[op->dest.reg].base = CFI_CFA;
+ state->vals[op->dest.reg].offset = \
+ -state->stack_size + op->src.offset;
+
+ break;
+ }
+
+ if (state->drap && op->dest.reg == CFI_SP &&
+ op->src.reg == state->drap_reg) {
+
+ /* drap: lea disp(%drap), %rsp */
+ cfa->base = CFI_SP;
+ cfa->offset = state->stack_size = -op->src.offset;
+ state->drap_reg = CFI_UNDEFINED;
+ state->drap = false;
+ break;
+ }
+
+ if (op->dest.reg == state->cfa.base) {
+ WARN_FUNC("unsupported stack register modification",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ break;
+
+ case OP_SRC_AND:
+ if (op->dest.reg != CFI_SP ||
+ (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
+ (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
+ WARN_FUNC("unsupported stack pointer realignment",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ if (state->drap_reg != CFI_UNDEFINED) {
+ /* drap: and imm, %rsp */
+ cfa->base = state->drap_reg;
+ cfa->offset = state->stack_size = 0;
+ state->drap = true;
+ }
+
+ /*
+ * Older versions of GCC (4.8ish) realign the stack
+ * without DRAP, with a frame pointer.
+ */
+
+ break;
+
+ case OP_SRC_POP:
+ if (!state->drap && op->dest.type == OP_DEST_REG &&
+ op->dest.reg == cfa->base) {
+
+ /* pop %rbp */
+ cfa->base = CFI_SP;
+ }
+
+ if (state->drap && cfa->base == CFI_BP_INDIRECT &&
+ op->dest.type == OP_DEST_REG &&
+ op->dest.reg == state->drap_reg &&
+ state->drap_offset == -state->stack_size) {
+
+ /* drap: pop %drap */
+ cfa->base = state->drap_reg;
+ cfa->offset = 0;
+ state->drap_offset = -1;
+
+ } else if (regs[op->dest.reg].offset == -state->stack_size) {
+
+ /* pop %reg */
+ restore_reg(state, op->dest.reg);
+ }
+
+ state->stack_size -= 8;
+ if (cfa->base == CFI_SP)
+ cfa->offset -= 8;
+
+ break;
+
+ case OP_SRC_REG_INDIRECT:
+ if (state->drap && op->src.reg == CFI_BP &&
+ op->src.offset == state->drap_offset) {
+
+ /* drap: mov disp(%rbp), %drap */
+ cfa->base = state->drap_reg;
+ cfa->offset = 0;
+ state->drap_offset = -1;
+ }
+
+ if (state->drap && op->src.reg == CFI_BP &&
+ op->src.offset == regs[op->dest.reg].offset) {
+
+ /* drap: mov disp(%rbp), %reg */
+ restore_reg(state, op->dest.reg);
+
+ } else if (op->src.reg == cfa->base &&
+ op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
+
+ /* mov disp(%rbp), %reg */
+ /* mov disp(%rsp), %reg */
+ restore_reg(state, op->dest.reg);
+ }
+
+ break;
+
+ default:
+ WARN_FUNC("unknown stack-related instruction",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ break;
+
+ case OP_DEST_PUSH:
+ state->stack_size += 8;
+ if (cfa->base == CFI_SP)
+ cfa->offset += 8;
+
+ if (op->src.type != OP_SRC_REG)
+ break;
+
+ if (state->drap) {
+ if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
+
+ /* drap: push %drap */
+ cfa->base = CFI_BP_INDIRECT;
+ cfa->offset = -state->stack_size;
+
+ /* save drap so we know when to restore it */
+ state->drap_offset = -state->stack_size;
+
+ } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
+
+ /* drap: push %rbp */
+ state->stack_size = 0;
+
+ } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
+
+ /* drap: push %reg */
+ save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
+ }
+
+ } else {
+
+ /* push %reg */
+ save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
+ }
+
+ /* detect when asm code uses rbp as a scratch register */
+ if (!no_fp && insn->func && op->src.reg == CFI_BP &&
+ cfa->base != CFI_BP)
+ state->bp_scratch = true;
+ break;
+
+ case OP_DEST_REG_INDIRECT:
+
+ if (state->drap) {
+ if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
+
+ /* drap: mov %drap, disp(%rbp) */
+ cfa->base = CFI_BP_INDIRECT;
+ cfa->offset = op->dest.offset;
+
+ /* save drap offset so we know when to restore it */
+ state->drap_offset = op->dest.offset;
+ }
+
+ else if (regs[op->src.reg].base == CFI_UNDEFINED) {
+
+ /* drap: mov reg, disp(%rbp) */
+ save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
+ }
+
+ } else if (op->dest.reg == cfa->base) {
+
+ /* mov reg, disp(%rbp) */
+ /* mov reg, disp(%rsp) */
+ save_reg(state, op->src.reg, CFI_CFA,
+ op->dest.offset - state->cfa.offset);
+ }
+
+ break;
+
+ case OP_DEST_LEAVE:
+ if ((!state->drap && cfa->base != CFI_BP) ||
+ (state->drap && cfa->base != state->drap_reg)) {
+ WARN_FUNC("leave instruction with modified stack frame",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ /* leave (mov %rbp, %rsp; pop %rbp) */
+
+ state->stack_size = -state->regs[CFI_BP].offset - 8;
+ restore_reg(state, CFI_BP);
+
+ if (!state->drap) {
+ cfa->base = CFI_SP;
+ cfa->offset -= 8;
+ }
+
+ break;
+
+ case OP_DEST_MEM:
+ if (op->src.type != OP_SRC_POP) {
+ WARN_FUNC("unknown stack-related memory operation",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ /* pop mem */
+ state->stack_size -= 8;
+ if (cfa->base == CFI_SP)
+ cfa->offset -= 8;
+
+ break;
+
+ default:
+ WARN_FUNC("unknown stack-related instruction",
+ insn->sec, insn->offset);
+ return -1;
+ }
+
+ return 0;
+}
+
+static bool insn_state_match(struct instruction *insn, struct insn_state *state)
+{
+ struct insn_state *state1 = &insn->state, *state2 = state;
+ int i;
+
+ if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
+ WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
+ insn->sec, insn->offset,
+ state1->cfa.base, state1->cfa.offset,
+ state2->cfa.base, state2->cfa.offset);
+
+ } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
+ for (i = 0; i < CFI_NUM_REGS; i++) {
+ if (!memcmp(&state1->regs[i], &state2->regs[i],
+ sizeof(struct cfi_reg)))
+ continue;
+
+ WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
+ insn->sec, insn->offset,
+ i, state1->regs[i].base, state1->regs[i].offset,
+ i, state2->regs[i].base, state2->regs[i].offset);
+ break;
+ }
+
+ } else if (state1->type != state2->type) {
+ WARN_FUNC("stack state mismatch: type1=%d type2=%d",
+ insn->sec, insn->offset, state1->type, state2->type);
+
+ } else if (state1->drap != state2->drap ||
+ (state1->drap && state1->drap_reg != state2->drap_reg) ||
+ (state1->drap && state1->drap_offset != state2->drap_offset)) {
+ WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
+ insn->sec, insn->offset,
+ state1->drap, state1->drap_reg, state1->drap_offset,
+ state2->drap, state2->drap_reg, state2->drap_offset);
+
+ } else
+ return true;
+
+ return false;
+}
+
+/*
+ * Follow the branch starting at the given instruction, and recursively follow
+ * any other branches (jumps). Meanwhile, track the frame pointer state at
+ * each instruction and validate all the rules described in
+ * tools/objtool/Documentation/stack-validation.txt.
+ */
+static int validate_branch(struct objtool_file *file, struct instruction *first,
+ struct insn_state state)
+{
+ struct alternative *alt;
+ struct instruction *insn, *next_insn;
+ struct section *sec;
+ struct symbol *func = NULL;
+ int ret;
+
+ insn = first;
+ sec = insn->sec;
+
+ if (insn->alt_group && list_empty(&insn->alts)) {
+ WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
+ sec, insn->offset);
+ return 1;
+ }
+
+ while (1) {
+ next_insn = next_insn_same_sec(file, insn);
+
+ if (file->c_file && func && insn->func && func != insn->func->pfunc) {
+ WARN("%s() falls through to next function %s()",
+ func->name, insn->func->name);
+ return 1;
+ }
+
+ if (insn->func)
+ func = insn->func->pfunc;
+
+ if (func && insn->ignore) {
+ WARN_FUNC("BUG: why am I validating an ignored function?",
+ sec, insn->offset);
+ return 1;
+ }
+
+ if (insn->visited) {
+ if (!insn->hint && !insn_state_match(insn, &state))
+ return 1;
+
+ return 0;
+ }
+
+ if (insn->hint) {
+ if (insn->restore) {
+ struct instruction *save_insn, *i;
+
+ i = insn;
+ save_insn = NULL;
+ func_for_each_insn_continue_reverse(file, insn->func, i) {
+ if (i->save) {
+ save_insn = i;
+ break;
+ }
+ }
+
+ if (!save_insn) {
+ WARN_FUNC("no corresponding CFI save for CFI restore",
+ sec, insn->offset);
+ return 1;
+ }
+
+ if (!save_insn->visited) {
+ /*
+ * Oops, no state to copy yet.
+ * Hopefully we can reach this
+ * instruction from another branch
+ * after the save insn has been
+ * visited.
+ */
+ if (insn == first)
+ return 0;
+
+ WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
+ sec, insn->offset);
+ return 1;
+ }
+
+ insn->state = save_insn->state;
+ }
+
+ state = insn->state;
+
+ } else
+ insn->state = state;
+
+ insn->visited = true;
+
+ if (!insn->ignore_alts) {
+ list_for_each_entry(alt, &insn->alts, list) {
+ ret = validate_branch(file, alt->insn, state);
+ if (ret)
+ return 1;
+ }
+ }
+
+ switch (insn->type) {
+
+ case INSN_RETURN:
+ if (func && has_modified_stack_frame(&state)) {
+ WARN_FUNC("return with modified stack frame",
+ sec, insn->offset);
+ return 1;
+ }
+
+ if (state.bp_scratch) {
+ WARN("%s uses BP as a scratch register",
+ insn->func->name);
+ return 1;
+ }
+
+ return 0;
+
+ case INSN_CALL:
+ if (is_fentry_call(insn))
+ break;
+
+ ret = dead_end_function(file, insn->call_dest);
+ if (ret == 1)
+ return 0;
+ if (ret == -1)
+ return 1;
+
+ /* fallthrough */
+ case INSN_CALL_DYNAMIC:
+ if (!no_fp && func && !has_valid_stack_frame(&state)) {
+ WARN_FUNC("call without frame pointer save/setup",
+ sec, insn->offset);
+ return 1;
+ }
+ break;
+
+ case INSN_JUMP_CONDITIONAL:
+ case INSN_JUMP_UNCONDITIONAL:
+ if (insn->jump_dest &&
+ (!func || !insn->jump_dest->func ||
+ insn->jump_dest->func->pfunc == func)) {
+ ret = validate_branch(file, insn->jump_dest,
+ state);
+ if (ret)
+ return 1;
+
+ } else if (func && has_modified_stack_frame(&state)) {
+ WARN_FUNC("sibling call from callable instruction with modified stack frame",
+ sec, insn->offset);
+ return 1;
+ }
+
+ if (insn->type == INSN_JUMP_UNCONDITIONAL)
+ return 0;
+
+ break;
+
+ case INSN_JUMP_DYNAMIC:
+ if (func && list_empty(&insn->alts) &&
+ has_modified_stack_frame(&state)) {
+ WARN_FUNC("sibling call from callable instruction with modified stack frame",
+ sec, insn->offset);
+ return 1;
+ }
+
+ return 0;
+
+ case INSN_CONTEXT_SWITCH:
+ if (func && (!next_insn || !next_insn->hint)) {
+ WARN_FUNC("unsupported instruction in callable function",
+ sec, insn->offset);
+ return 1;
+ }
+ return 0;
+
+ case INSN_STACK:
+ if (update_insn_state(insn, &state))
+ return 1;
+
+ break;
+
+ default:
+ break;
+ }
+
+ if (insn->dead_end)
+ return 0;
+
+ if (!next_insn) {
+ if (state.cfa.base == CFI_UNDEFINED)
+ return 0;
+ WARN("%s: unexpected end of section", sec->name);
+ return 1;
+ }
+
+ insn = next_insn;
+ }
+
+ return 0;
+}
+
+static int validate_unwind_hints(struct objtool_file *file)
+{
+ struct instruction *insn;
+ int ret, warnings = 0;
+ struct insn_state state;
+
+ if (!file->hints)
+ return 0;
+
+ clear_insn_state(&state);
+
+ for_each_insn(file, insn) {
+ if (insn->hint && !insn->visited) {
+ ret = validate_branch(file, insn, state);
+ warnings += ret;
+ }
+ }
+
+ return warnings;
+}
+
+static int validate_retpoline(struct objtool_file *file)
+{
+ struct instruction *insn;
+ int warnings = 0;
+
+ for_each_insn(file, insn) {
+ if (insn->type != INSN_JUMP_DYNAMIC &&
+ insn->type != INSN_CALL_DYNAMIC)
+ continue;
+
+ if (insn->retpoline_safe)
+ continue;
+
+ /*
+ * .init.text code is ran before userspace and thus doesn't
+ * strictly need retpolines, except for modules which are
+ * loaded late, they very much do need retpoline in their
+ * .init.text
+ */
+ if (!strcmp(insn->sec->name, ".init.text") && !module)
+ continue;
+
+ WARN_FUNC("indirect %s found in RETPOLINE build",
+ insn->sec, insn->offset,
+ insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+
+ warnings++;
+ }
+
+ return warnings;
+}
+
+static bool is_kasan_insn(struct instruction *insn)
+{
+ return (insn->type == INSN_CALL &&
+ !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
+}
+
+static bool is_ubsan_insn(struct instruction *insn)
+{
+ return (insn->type == INSN_CALL &&
+ !strcmp(insn->call_dest->name,
+ "__ubsan_handle_builtin_unreachable"));
+}
+
+static bool ignore_unreachable_insn(struct instruction *insn)
+{
+ int i;
+
+ if (insn->ignore || insn->type == INSN_NOP)
+ return true;
+
+ /*
+ * Ignore any unused exceptions. This can happen when a whitelisted
+ * function has an exception table entry.
+ *
+ * Also ignore alternative replacement instructions. This can happen
+ * when a whitelisted function uses one of the ALTERNATIVE macros.
+ */
+ if (!strcmp(insn->sec->name, ".fixup") ||
+ !strcmp(insn->sec->name, ".altinstr_replacement") ||
+ !strcmp(insn->sec->name, ".altinstr_aux"))
+ return true;
+
+ if (!insn->func)
+ return false;
+
+ /*
+ * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
+ * __builtin_unreachable(). The BUG() macro has an unreachable() after
+ * the UD2, which causes GCC's undefined trap logic to emit another UD2
+ * (or occasionally a JMP to UD2).
+ */
+ if (list_prev_entry(insn, list)->dead_end &&
+ (insn->type == INSN_BUG ||
+ (insn->type == INSN_JUMP_UNCONDITIONAL &&
+ insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
+ return true;
+
+ /*
+ * Check if this (or a subsequent) instruction is related to
+ * CONFIG_UBSAN or CONFIG_KASAN.
+ *
+ * End the search at 5 instructions to avoid going into the weeds.
+ */
+ for (i = 0; i < 5; i++) {
+
+ if (is_kasan_insn(insn) || is_ubsan_insn(insn))
+ return true;
+
+ if (insn->type == INSN_JUMP_UNCONDITIONAL) {
+ if (insn->jump_dest &&
+ insn->jump_dest->func == insn->func) {
+ insn = insn->jump_dest;
+ continue;
+ }
+
+ break;
+ }
+
+ if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
+ break;
+
+ insn = list_next_entry(insn, list);
+ }
+
+ return false;
+}
+
+static int validate_functions(struct objtool_file *file)
+{
+ struct section *sec;
+ struct symbol *func;
+ struct instruction *insn;
+ struct insn_state state;
+ int ret, warnings = 0;
+
+ clear_insn_state(&state);
+
+ state.cfa = initial_func_cfi.cfa;
+ memcpy(&state.regs, &initial_func_cfi.regs,
+ CFI_NUM_REGS * sizeof(struct cfi_reg));
+ state.stack_size = initial_func_cfi.cfa.offset;
+
+ for_each_sec(file, sec) {
+ list_for_each_entry(func, &sec->symbol_list, list) {
+ if (func->type != STT_FUNC || func->pfunc != func)
+ continue;
+
+ insn = find_insn(file, sec, func->offset);
+ if (!insn || insn->ignore)
+ continue;
+
+ ret = validate_branch(file, insn, state);
+ warnings += ret;
+ }
+ }
+
+ return warnings;
+}
+
+static int validate_reachable_instructions(struct objtool_file *file)
+{
+ struct instruction *insn;
+
+ if (file->ignore_unreachables)
+ return 0;
+
+ for_each_insn(file, insn) {
+ if (insn->visited || ignore_unreachable_insn(insn))
+ continue;
+
+ WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
+ return 1;
+ }
+
+ return 0;
+}
+
+static void cleanup(struct objtool_file *file)
+{
+ struct instruction *insn, *tmpinsn;
+ struct alternative *alt, *tmpalt;
+
+ list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
+ list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
+ list_del(&alt->list);
+ free(alt);
+ }
+ list_del(&insn->list);
+ hash_del(&insn->hash);
+ free(insn);
+ }
+ elf_close(file->elf);
+}
+
+static struct objtool_file file;
+
+int check(const char *_objname, bool orc)
+{
+ int ret, warnings = 0;
+
+ objname = _objname;
+
+ file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
+ if (!file.elf)
+ return 1;
+
+ INIT_LIST_HEAD(&file.insn_list);
+ hash_init(file.insn_hash);
+ file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
+ file.c_file = find_section_by_name(file.elf, ".comment");
+ file.ignore_unreachables = no_unreachable;
+ file.hints = false;
+
+ arch_initial_func_cfi_state(&initial_func_cfi);
+
+ ret = decode_sections(&file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+
+ if (list_empty(&file.insn_list))
+ goto out;
+
+ if (retpoline) {
+ ret = validate_retpoline(&file);
+ if (ret < 0)
+ return ret;
+ warnings += ret;
+ }
+
+ ret = validate_functions(&file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+
+ ret = validate_unwind_hints(&file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+
+ if (!warnings) {
+ ret = validate_reachable_instructions(&file);
+ if (ret < 0)
+ goto out;
+ warnings += ret;
+ }
+
+ if (orc) {
+ ret = create_orc(&file);
+ if (ret < 0)
+ goto out;
+
+ ret = create_orc_sections(&file);
+ if (ret < 0)
+ goto out;
+
+ ret = elf_write(file.elf);
+ if (ret < 0)
+ goto out;
+ }
+
+out:
+ cleanup(&file);
+
+ /* ignore warnings for now until we get all the code cleaned up */
+ if (ret || warnings)
+ return 0;
+ return 0;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-24 20:45:42 +0000