This is a note to let you know that I've just added the patch titled
x86/alternatives: Remove faulty optimization
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-alternatives-remove-faulty-optimization.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4ba89dd6ddeca2a733bdaed7c9a5cbe4e19d9124 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Date: Mon, 4 Sep 2023 22:04:54 -0700
Subject: x86/alternatives: Remove faulty optimization
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
commit 4ba89dd6ddeca2a733bdaed7c9a5cbe4e19d9124 upstream.
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>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.1693889988.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/alternative.c | 8 --------
1 file changed, 8 deletions(-)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -720,14 +720,6 @@ void __init_or_module noinline apply_ret
{
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;
Patches currently in stable-queue which might be from jpoimboe@xxxxxxxxxx are
queue-6.5/x86-alternatives-remove-faulty-optimization.patch
