[tip: x86/bugs] x86/alternatives: Remove faulty optimization
From: tip-bot2 for Josh Poimboeuf
Date: Tue Sep 05 2023 - 12:35:29 EST
The following commit has been merged into the x86/bugs branch of tip:
Commit-ID: 85d5fbfb7deaf3a5b4666e741bb72a68866439e6
Gitweb: https://git.kernel.org/tip/85d5fbfb7deaf3a5b4666e741bb72a68866439e6
Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Mon, 04 Sep 2023 22:04:54 -07:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 05 Sep 2023 12:05:07 +02:00
x86/alternatives: Remove faulty optimization
The following commit
095b8303f383 ("x86/alternative: Make custom return thunk unconditional")
made '__x86_return_thunk' a placeholder value. All code setting
X86_FEATURE_RETHUNK also changes the value of 'x86_return_thunk'. So
the optimization at the beginning of apply_returns() is dead code.
Also, before the above-mentioned commit, the optimization actually had a
bug It bypassed __static_call_fixup(), causing some raw returns to
remain unpatched in static call trampolines. Thus the 'Fixes' tag.
Fixes: d2408e043e72 ("x86/alternative: Optimize returns patching")
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.1693889988.git.jpoimboe@xxxxxxxxxx
---
arch/x86/kernel/alternative.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a5ead6a..c850f5a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -720,14 +720,6 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
{
s32 *s;
- /*
- * Do not patch out the default return thunks if those needed are the
- * ones generated by the compiler.
- */
- if (cpu_feature_enabled(X86_FEATURE_RETHUNK) &&
- (x86_return_thunk == __x86_return_thunk))
- return;
-
for (s = start; s < end; s++) {
void *dest = NULL, *addr = (void *)s + *s;
struct insn insn;