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kmsan: allow using __msan_instrument_asm_store() inside runtime

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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 <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Alexander Potapenko 2022-11-28 10:45:41 +01:00 • committed by Andrew Morton
parent 1e8e4a7cc2
commit 85716a80c1
1 changed files with 5 additions and 3 deletions
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8
mm/kmsan/instrumentation.c
View file

@ -81,12 +81,16 @@ DECLARE_METADATA_PTR_GETTER(8);
* Handle a memory store performed by inline assembly. KMSAN conservatively * Handle a memory store performed by inline assembly. KMSAN conservatively
* attempts to unpoison the outputs of asm() directives to prevent false * attempts to unpoison the outputs of asm() directives to prevent false
* positives caused by missed stores. * 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) void __msan_instrument_asm_store(void *addr, uintptr_t size)
{ {
unsigned long ua_flags; unsigned long ua_flags;
if (!kmsan_enabled || kmsan_in_runtime()) if (!kmsan_enabled)
return; return;
ua_flags = user_access_save(); ua_flags = user_access_save();
@ -103,10 +107,8 @@ void __msan_instrument_asm_store(void *addr, uintptr_t size)
user_access_restore(ua_flags); user_access_restore(ua_flags);
return; return;
} }
kmsan_enter_runtime();
/* Unpoisoning the memory on best effort. */ /* Unpoisoning the memory on best effort. */
kmsan_internal_unpoison_memory(addr, size, /*checked*/ false); kmsan_internal_unpoison_memory(addr, size, /*checked*/ false);
kmsan_leave_runtime();
user_access_restore(ua_flags); user_access_restore(ua_flags);
} }
EXPORT_SYMBOL(__msan_instrument_asm_store); EXPORT_SYMBOL(__msan_instrument_asm_store);