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-rw-r--r--arch/arm64/kernel/module-plts.c368
1 files changed, 368 insertions, 0 deletions
diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c
new file mode 100644
index 000000000..79200f21e
--- /dev/null
+++ b/arch/arm64/kernel/module-plts.c
@@ -0,0 +1,368 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/elf.h>
+#include <linux/ftrace.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleloader.h>
+#include <linux/sort.h>
+
+static struct plt_entry __get_adrp_add_pair(u64 dst, u64 pc,
+ enum aarch64_insn_register reg)
+{
+ u32 adrp, add;
+
+ adrp = aarch64_insn_gen_adr(pc, dst, reg, AARCH64_INSN_ADR_TYPE_ADRP);
+ add = aarch64_insn_gen_add_sub_imm(reg, reg, dst % SZ_4K,
+ AARCH64_INSN_VARIANT_64BIT,
+ AARCH64_INSN_ADSB_ADD);
+
+ return (struct plt_entry){ cpu_to_le32(adrp), cpu_to_le32(add) };
+}
+
+struct plt_entry get_plt_entry(u64 dst, void *pc)
+{
+ struct plt_entry plt;
+ static u32 br;
+
+ if (!br)
+ br = aarch64_insn_gen_branch_reg(AARCH64_INSN_REG_16,
+ AARCH64_INSN_BRANCH_NOLINK);
+
+ plt = __get_adrp_add_pair(dst, (u64)pc, AARCH64_INSN_REG_16);
+ plt.br = cpu_to_le32(br);
+
+ return plt;
+}
+
+static bool plt_entries_equal(const struct plt_entry *a,
+ const struct plt_entry *b)
+{
+ u64 p, q;
+
+ /*
+ * Check whether both entries refer to the same target:
+ * do the cheapest checks first.
+ * If the 'add' or 'br' opcodes are different, then the target
+ * cannot be the same.
+ */
+ if (a->add != b->add || a->br != b->br)
+ return false;
+
+ p = ALIGN_DOWN((u64)a, SZ_4K);
+ q = ALIGN_DOWN((u64)b, SZ_4K);
+
+ /*
+ * If the 'adrp' opcodes are the same then we just need to check
+ * that they refer to the same 4k region.
+ */
+ if (a->adrp == b->adrp && p == q)
+ return true;
+
+ return (p + aarch64_insn_adrp_get_offset(le32_to_cpu(a->adrp))) ==
+ (q + aarch64_insn_adrp_get_offset(le32_to_cpu(b->adrp)));
+}
+
+u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
+ void *loc, const Elf64_Rela *rela,
+ Elf64_Sym *sym)
+{
+ struct mod_plt_sec *pltsec = !within_module_init((unsigned long)loc, mod) ?
+ &mod->arch.core : &mod->arch.init;
+ struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;
+ int i = pltsec->plt_num_entries;
+ int j = i - 1;
+ u64 val = sym->st_value + rela->r_addend;
+
+ if (is_forbidden_offset_for_adrp(&plt[i].adrp))
+ i++;
+
+ plt[i] = get_plt_entry(val, &plt[i]);
+
+ /*
+ * Check if the entry we just created is a duplicate. Given that the
+ * relocations are sorted, this will be the last entry we allocated.
+ * (if one exists).
+ */
+ if (j >= 0 && plt_entries_equal(plt + i, plt + j))
+ return (u64)&plt[j];
+
+ pltsec->plt_num_entries += i - j;
+ if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
+ return 0;
+
+ return (u64)&plt[i];
+}
+
+#ifdef CONFIG_ARM64_ERRATUM_843419
+u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,
+ void *loc, u64 val)
+{
+ struct mod_plt_sec *pltsec = !within_module_init((unsigned long)loc, mod) ?
+ &mod->arch.core : &mod->arch.init;
+ struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;
+ int i = pltsec->plt_num_entries++;
+ u32 br;
+ int rd;
+
+ if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
+ return 0;
+
+ if (is_forbidden_offset_for_adrp(&plt[i].adrp))
+ i = pltsec->plt_num_entries++;
+
+ /* get the destination register of the ADRP instruction */
+ rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD,
+ le32_to_cpup((__le32 *)loc));
+
+ br = aarch64_insn_gen_branch_imm((u64)&plt[i].br, (u64)loc + 4,
+ AARCH64_INSN_BRANCH_NOLINK);
+
+ plt[i] = __get_adrp_add_pair(val, (u64)&plt[i], rd);
+ plt[i].br = cpu_to_le32(br);
+
+ return (u64)&plt[i];
+}
+#endif
+
+#define cmp_3way(a, b) ((a) < (b) ? -1 : (a) > (b))
+
+static int cmp_rela(const void *a, const void *b)
+{
+ const Elf64_Rela *x = a, *y = b;
+ int i;
+
+ /* sort by type, symbol index and addend */
+ i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info));
+ if (i == 0)
+ i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info));
+ if (i == 0)
+ i = cmp_3way(x->r_addend, y->r_addend);
+ return i;
+}
+
+static bool duplicate_rel(const Elf64_Rela *rela, int num)
+{
+ /*
+ * Entries are sorted by type, symbol index and addend. That means
+ * that, if a duplicate entry exists, it must be in the preceding
+ * slot.
+ */
+ return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0;
+}
+
+static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num,
+ Elf64_Word dstidx, Elf_Shdr *dstsec)
+{
+ unsigned int ret = 0;
+ Elf64_Sym *s;
+ int i;
+
+ for (i = 0; i < num; i++) {
+ u64 min_align;
+
+ switch (ELF64_R_TYPE(rela[i].r_info)) {
+ case R_AARCH64_JUMP26:
+ case R_AARCH64_CALL26:
+ /*
+ * We only have to consider branch targets that resolve
+ * to symbols that are defined in a different section.
+ * This is not simply a heuristic, it is a fundamental
+ * limitation, since there is no guaranteed way to emit
+ * PLT entries sufficiently close to the branch if the
+ * section size exceeds the range of a branch
+ * instruction. So ignore relocations against defined
+ * symbols if they live in the same section as the
+ * relocation target.
+ */
+ s = syms + ELF64_R_SYM(rela[i].r_info);
+ if (s->st_shndx == dstidx)
+ break;
+
+ /*
+ * Jump relocations with non-zero addends against
+ * undefined symbols are supported by the ELF spec, but
+ * do not occur in practice (e.g., 'jump n bytes past
+ * the entry point of undefined function symbol f').
+ * So we need to support them, but there is no need to
+ * take them into consideration when trying to optimize
+ * this code. So let's only check for duplicates when
+ * the addend is zero: this allows us to record the PLT
+ * entry address in the symbol table itself, rather than
+ * having to search the list for duplicates each time we
+ * emit one.
+ */
+ if (rela[i].r_addend != 0 || !duplicate_rel(rela, i))
+ ret++;
+ break;
+ case R_AARCH64_ADR_PREL_PG_HI21_NC:
+ case R_AARCH64_ADR_PREL_PG_HI21:
+ if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) ||
+ !cpus_have_const_cap(ARM64_WORKAROUND_843419))
+ break;
+
+ /*
+ * Determine the minimal safe alignment for this ADRP
+ * instruction: the section alignment at which it is
+ * guaranteed not to appear at a vulnerable offset.
+ *
+ * This comes down to finding the least significant zero
+ * bit in bits [11:3] of the section offset, and
+ * increasing the section's alignment so that the
+ * resulting address of this instruction is guaranteed
+ * to equal the offset in that particular bit (as well
+ * as all less significant bits). This ensures that the
+ * address modulo 4 KB != 0xfff8 or 0xfffc (which would
+ * have all ones in bits [11:3])
+ */
+ min_align = 2ULL << ffz(rela[i].r_offset | 0x7);
+
+ /*
+ * Allocate veneer space for each ADRP that may appear
+ * at a vulnerable offset nonetheless. At relocation
+ * time, some of these will remain unused since some
+ * ADRP instructions can be patched to ADR instructions
+ * instead.
+ */
+ if (min_align > SZ_4K)
+ ret++;
+ else
+ dstsec->sh_addralign = max(dstsec->sh_addralign,
+ min_align);
+ break;
+ }
+ }
+
+ if (IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) &&
+ cpus_have_const_cap(ARM64_WORKAROUND_843419))
+ /*
+ * Add some slack so we can skip PLT slots that may trigger
+ * the erratum due to the placement of the ADRP instruction.
+ */
+ ret += DIV_ROUND_UP(ret, (SZ_4K / sizeof(struct plt_entry)));
+
+ return ret;
+}
+
+static bool branch_rela_needs_plt(Elf64_Sym *syms, Elf64_Rela *rela,
+ Elf64_Word dstidx)
+{
+
+ Elf64_Sym *s = syms + ELF64_R_SYM(rela->r_info);
+
+ if (s->st_shndx == dstidx)
+ return false;
+
+ return ELF64_R_TYPE(rela->r_info) == R_AARCH64_JUMP26 ||
+ ELF64_R_TYPE(rela->r_info) == R_AARCH64_CALL26;
+}
+
+/* Group branch PLT relas at the front end of the array. */
+static int partition_branch_plt_relas(Elf64_Sym *syms, Elf64_Rela *rela,
+ int numrels, Elf64_Word dstidx)
+{
+ int i = 0, j = numrels - 1;
+
+ while (i < j) {
+ if (branch_rela_needs_plt(syms, &rela[i], dstidx))
+ i++;
+ else if (branch_rela_needs_plt(syms, &rela[j], dstidx))
+ swap(rela[i], rela[j]);
+ else
+ j--;
+ }
+
+ return i;
+}
+
+int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
+ char *secstrings, struct module *mod)
+{
+ unsigned long core_plts = 0;
+ unsigned long init_plts = 0;
+ Elf64_Sym *syms = NULL;
+ Elf_Shdr *pltsec, *tramp = NULL;
+ int i;
+
+ /*
+ * Find the empty .plt section so we can expand it to store the PLT
+ * entries. Record the symtab address as well.
+ */
+ for (i = 0; i < ehdr->e_shnum; i++) {
+ if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
+ mod->arch.core.plt_shndx = i;
+ else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
+ mod->arch.init.plt_shndx = i;
+ else if (!strcmp(secstrings + sechdrs[i].sh_name,
+ ".text.ftrace_trampoline"))
+ tramp = sechdrs + i;
+ else if (sechdrs[i].sh_type == SHT_SYMTAB)
+ syms = (Elf64_Sym *)sechdrs[i].sh_addr;
+ }
+
+ if (!mod->arch.core.plt_shndx || !mod->arch.init.plt_shndx) {
+ pr_err("%s: module PLT section(s) missing\n", mod->name);
+ return -ENOEXEC;
+ }
+ if (!syms) {
+ pr_err("%s: module symtab section missing\n", mod->name);
+ return -ENOEXEC;
+ }
+
+ for (i = 0; i < ehdr->e_shnum; i++) {
+ Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset;
+ int nents, numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela);
+ Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info;
+
+ if (sechdrs[i].sh_type != SHT_RELA)
+ continue;
+
+ /* ignore relocations that operate on non-exec sections */
+ if (!(dstsec->sh_flags & SHF_EXECINSTR))
+ continue;
+
+ /*
+ * sort branch relocations requiring a PLT by type, symbol index
+ * and addend
+ */
+ nents = partition_branch_plt_relas(syms, rels, numrels,
+ sechdrs[i].sh_info);
+ if (nents)
+ sort(rels, nents, sizeof(Elf64_Rela), cmp_rela, NULL);
+
+ if (!module_init_layout_section(secstrings + dstsec->sh_name))
+ core_plts += count_plts(syms, rels, numrels,
+ sechdrs[i].sh_info, dstsec);
+ else
+ init_plts += count_plts(syms, rels, numrels,
+ sechdrs[i].sh_info, dstsec);
+ }
+
+ pltsec = sechdrs + mod->arch.core.plt_shndx;
+ pltsec->sh_type = SHT_NOBITS;
+ pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+ pltsec->sh_addralign = L1_CACHE_BYTES;
+ pltsec->sh_size = (core_plts + 1) * sizeof(struct plt_entry);
+ mod->arch.core.plt_num_entries = 0;
+ mod->arch.core.plt_max_entries = core_plts;
+
+ pltsec = sechdrs + mod->arch.init.plt_shndx;
+ pltsec->sh_type = SHT_NOBITS;
+ pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+ pltsec->sh_addralign = L1_CACHE_BYTES;
+ pltsec->sh_size = (init_plts + 1) * sizeof(struct plt_entry);
+ mod->arch.init.plt_num_entries = 0;
+ mod->arch.init.plt_max_entries = init_plts;
+
+ if (tramp) {
+ tramp->sh_type = SHT_NOBITS;
+ tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+ tramp->sh_addralign = __alignof__(struct plt_entry);
+ tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry);
+ }
+
+ return 0;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-07-23 15:18:32 +0000