Commit 4ba89dd6 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Borislav Petkov (AMD)
Browse files

x86/alternatives: Remove faulty optimization 



The following commit

  095b8303 ("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: d2408e04 ("x86/alternative: Optimize returns patching")
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Acked-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.1693889988.git.jpoimboe@kernel.org
parent ce9ecca0

arch/x86/kernel/alternative.c

+0 −8
Original line number Diff line number Diff line
@@ -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;