RET = 3, /* tramp / site cond-tail-call */
};
+/*
+ * 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 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
-static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
+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;
break;
case RET:
- code = &retinsn;
+ if (cpu_feature_enabled(X86_FEATURE_RETHUNK))
+ code = text_gen_insn(JMP32_INSN_OPCODE, insn, &__x86_return_thunk);
+ else
+ code = &retinsn;
break;
}
if (memcmp(insn, code, size) == 0)
return;
- if (unlikely(system_state == SYSTEM_BOOTING))
+ if (system_state == SYSTEM_BOOTING || modinit)
return text_poke_early(insn, code, size);
text_poke_bp(insn, code, size, emulate);
{
u8 opcode = *(u8 *)insn;
- if (tramp && memcmp(insn+5, "SCT", 3)) {
+ if (tramp && memcmp(insn+5, tramp_ud, 3)) {
pr_err("trampoline signature fail");
BUG();
}
if (tramp) {
__static_call_validate(tramp, true, true);
- __static_call_transform(tramp, __sc_insn(!func, true), func);
+ __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);
+ __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)
+{
+ 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