From 85716a80c16dd6b6d1aaed87cd4b91c9b1d9b9b2 Mon Sep 17 00:00:00 2001 From: Alexander Potapenko Date: Mon, 28 Nov 2022 10:45:41 +0100 Subject: [PATCH] kmsan: allow using __msan_instrument_asm_store() inside runtime In certain cases (e.g. when handling a softirq) __msan_instrument_asm_store(&var, sizeof(var)) may be called with from within KMSAN runtime, but later the value of @var is used with !kmsan_in_runtime(), leading to false positives. Because kmsan_internal_unpoison_memory() doesn't take locks, it should be fine to call it without kmsan_in_runtime() checks, which fixes the mentioned false positives. Link: https://lkml.kernel.org/r/20221128094541.2645890-2-glider@google.com Signed-off-by: Alexander Potapenko Cc: Dmitry Vyukov Cc: Eric Biggers Cc: Ingo Molnar Cc: Marco Elver Cc: Peter Zijlstra Cc: Will Deacon Signed-off-by: Andrew Morton --- mm/kmsan/instrumentation.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/kmsan/instrumentation.c b/mm/kmsan/instrumentation.c index 271f135f97a1..770fe02904f3 100644 --- a/mm/kmsan/instrumentation.c +++ b/mm/kmsan/instrumentation.c @@ -81,12 +81,16 @@ DECLARE_METADATA_PTR_GETTER(8); * Handle a memory store performed by inline assembly. KMSAN conservatively * attempts to unpoison the outputs of asm() directives to prevent false * positives caused by missed stores. + * + * __msan_instrument_asm_store() may be called for inline assembly code when + * entering or leaving IRQ. We omit the check for kmsan_in_runtime() to ensure + * the memory written to in these cases is also marked as initialized. */ void __msan_instrument_asm_store(void *addr, uintptr_t size) { unsigned long ua_flags; - if (!kmsan_enabled || kmsan_in_runtime()) + if (!kmsan_enabled) return; ua_flags = user_access_save(); @@ -103,10 +107,8 @@ void __msan_instrument_asm_store(void *addr, uintptr_t size) user_access_restore(ua_flags); return; } - kmsan_enter_runtime(); /* Unpoisoning the memory on best effort. */ kmsan_internal_unpoison_memory(addr, size, /*checked*/ false); - kmsan_leave_runtime(); user_access_restore(ua_flags); } EXPORT_SYMBOL(__msan_instrument_asm_store);