From 85716a80c16dd6b6d1aaed87cd4b91c9b1d9b9b2 Mon Sep 17 00:00:00 2001
From: Alexander Potapenko <glider@google.com>
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 <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>
---
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);
--
2.42.0