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-rw-r--r--arch/x86/kernel/static_call.c212
1 files changed, 212 insertions, 0 deletions
diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
new file mode 100644
index 000000000..3fbb49168
--- /dev/null
+++ b/arch/x86/kernel/static_call.c
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/static_call.h>
+#include <linux/memory.h>
+#include <linux/bug.h>
+#include <asm/text-patching.h>
+
+enum insn_type {
+ CALL = 0, /* site call */
+ NOP = 1, /* site cond-call */
+ JMP = 2, /* tramp / site tail-call */
+ RET = 3, /* tramp / site cond-tail-call */
+ JCC = 4,
+};
+
+/*
+ * ud1 %esp, %ecx - a 3 byte #UD that is unique to trampolines, chosen such
+ * that there is no false-positive trampoline identification while also being a
+ * speculation stop.
+ */
+static const u8 tramp_ud[] = { 0x0f, 0xb9, 0xcc };
+
+/*
+ * cs cs cs xorl %eax, %eax - a single 5 byte instruction that clears %[er]ax
+ */
+static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 };
+
+static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
+
+static u8 __is_Jcc(u8 *insn) /* Jcc.d32 */
+{
+ u8 ret = 0;
+
+ if (insn[0] == 0x0f) {
+ u8 tmp = insn[1];
+ if ((tmp & 0xf0) == 0x80)
+ ret = tmp;
+ }
+
+ return ret;
+}
+
+extern void __static_call_return(void);
+
+asm (".global __static_call_return\n\t"
+ ".type __static_call_return, @function\n\t"
+ "__static_call_return:\n\t"
+ ANNOTATE_NOENDBR
+ ANNOTATE_RETPOLINE_SAFE
+ "ret; int3\n\t"
+ ".size __static_call_return, . - __static_call_return \n\t");
+
+static void __ref __static_call_transform(void *insn, enum insn_type type,
+ void *func, bool modinit)
+{
+ const void *emulate = NULL;
+ int size = CALL_INSN_SIZE;
+ const void *code;
+ u8 op, buf[6];
+
+ if ((type == JMP || type == RET) && (op = __is_Jcc(insn)))
+ type = JCC;
+
+ switch (type) {
+ case CALL:
+ code = text_gen_insn(CALL_INSN_OPCODE, insn, func);
+ if (func == &__static_call_return0) {
+ emulate = code;
+ code = &xor5rax;
+ }
+
+ break;
+
+ case NOP:
+ code = x86_nops[5];
+ break;
+
+ case JMP:
+ code = text_gen_insn(JMP32_INSN_OPCODE, insn, func);
+ break;
+
+ case RET:
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+ code = text_gen_insn(JMP32_INSN_OPCODE, insn, &__x86_return_thunk);
+ else
+ code = &retinsn;
+ break;
+
+ case JCC:
+ if (!func) {
+ func = __static_call_return;
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+ func = __x86_return_thunk;
+ }
+
+ buf[0] = 0x0f;
+ __text_gen_insn(buf+1, op, insn+1, func, 5);
+ code = buf;
+ size = 6;
+
+ break;
+ }
+
+ if (memcmp(insn, code, size) == 0)
+ return;
+
+ if (system_state == SYSTEM_BOOTING || modinit)
+ return text_poke_early(insn, code, size);
+
+ text_poke_bp(insn, code, size, emulate);
+}
+
+static void __static_call_validate(u8 *insn, bool tail, bool tramp)
+{
+ u8 opcode = insn[0];
+
+ if (tramp && memcmp(insn+5, tramp_ud, 3)) {
+ pr_err("trampoline signature fail");
+ BUG();
+ }
+
+ if (tail) {
+ if (opcode == JMP32_INSN_OPCODE ||
+ opcode == RET_INSN_OPCODE ||
+ __is_Jcc(insn))
+ return;
+ } else {
+ if (opcode == CALL_INSN_OPCODE ||
+ !memcmp(insn, x86_nops[5], 5) ||
+ !memcmp(insn, xor5rax, 5))
+ return;
+ }
+
+ /*
+ * If we ever trigger this, our text is corrupt, we'll probably not live long.
+ */
+ pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn);
+ BUG();
+}
+
+static inline enum insn_type __sc_insn(bool null, bool tail)
+{
+ /*
+ * Encode the following table without branches:
+ *
+ * tail null insn
+ * -----+-------+------
+ * 0 | 0 | CALL
+ * 0 | 1 | NOP
+ * 1 | 0 | JMP
+ * 1 | 1 | RET
+ */
+ return 2*tail + null;
+}
+
+void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
+{
+ mutex_lock(&text_mutex);
+
+ if (tramp) {
+ __static_call_validate(tramp, true, true);
+ __static_call_transform(tramp, __sc_insn(!func, true), func, false);
+ }
+
+ if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
+ __static_call_validate(site, tail, false);
+ __static_call_transform(site, __sc_insn(!func, tail), func, false);
+ }
+
+ mutex_unlock(&text_mutex);
+}
+EXPORT_SYMBOL_GPL(arch_static_call_transform);
+
+#ifdef CONFIG_RETHUNK
+/*
+ * This is called by apply_returns() to fix up static call trampolines,
+ * specifically ARCH_DEFINE_STATIC_CALL_NULL_TRAMP which is recorded as
+ * having a return trampoline.
+ *
+ * The problem is that static_call() is available before determining
+ * X86_FEATURE_RETHUNK and, by implication, running alternatives.
+ *
+ * This means that __static_call_transform() above can have overwritten the
+ * return trampoline and we now need to fix things up to be consistent.
+ */
+bool __static_call_fixup(void *tramp, u8 op, void *dest)
+{
+ unsigned long addr = (unsigned long)tramp;
+ /*
+ * Not all .return_sites are a static_call trampoline (most are not).
+ * Check if the 3 bytes after the return are still kernel text, if not,
+ * then this definitely is not a trampoline and we need not worry
+ * further.
+ *
+ * This avoids the memcmp() below tripping over pagefaults etc..
+ */
+ if (((addr >> PAGE_SHIFT) != ((addr + 7) >> PAGE_SHIFT)) &&
+ !kernel_text_address(addr + 7))
+ return false;
+
+ if (memcmp(tramp+5, tramp_ud, 3)) {
+ /* Not a trampoline site, not our problem. */
+ return false;
+ }
+
+ mutex_lock(&text_mutex);
+ if (op == RET_INSN_OPCODE || dest == &__x86_return_thunk)
+ __static_call_transform(tramp, RET, NULL, true);
+ mutex_unlock(&text_mutex);
+
+ return true;
+}
+#endif