From 4ba89dd6ddeca2a733bdaed7c9a5cbe4e19d9124 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 4 Sep 2023 22:04:54 -0700 Subject: 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 Signed-off-by: Ingo Molnar Signed-off-by: Borislav Petkov (AMD) Acked-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.1693889988.git.jpoimboe@kernel.org --- 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 a5ead6a6d233..c850f5a9b1bb 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; -- cgit From aee9d30b9744d677509ef790f30f3a24c7841c3d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 22 Sep 2023 10:12:25 +0000 Subject: x86,static_call: Fix static-call vs return-thunk Commit 7825451fa4dc ("static_call: Add call depth tracking support") failed to realize the problem fixed there is not specific to call depth tracking but applies to all return-thunk uses. Move the fix to the appropriate place and condition. Fixes: ee88d363d156 ("x86,static_call: Use alternative RET encoding") Reported-by: David Kaplan Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Ingo Molnar Tested-by: Borislav Petkov (AMD) Cc: --- arch/x86/kernel/alternative.c | 3 +++ arch/x86/kernel/callthunks.c | 1 - 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index c850f5a9b1bb..517ee01503be 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -720,6 +720,9 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end) { s32 *s; + if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + static_call_force_reinit(); + for (s = start; s < end; s++) { void *dest = NULL, *addr = (void *)s + *s; struct insn insn; diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c index c06bfc086565..faa9f2299848 100644 --- a/arch/x86/kernel/callthunks.c +++ b/arch/x86/kernel/callthunks.c @@ -272,7 +272,6 @@ void __init callthunks_patch_builtin_calls(void) pr_info("Setting up call depth tracking\n"); mutex_lock(&text_mutex); callthunks_setup(&cs, &builtin_coretext); - static_call_force_reinit(); thunks_initialized = true; mutex_unlock(&text_mutex); } -- cgit