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x86/alternatives: Remove faulty optimization

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  095b8303f3 ("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: d2408e043e ("x86/alternative: Optimize returns patching")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.1693889988.git.jpoimboe@kernel.org
This commit is contained in:
Josh Poimboeuf 2023-09-04 22:04:54 -07:00 committed by Borislav Petkov (AMD)
parent ce9ecca023
commit 4ba89dd6dd
1 changed files with 0 additions and 8 deletions
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8
arch/x86/kernel/alternative.c
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@ -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;