The patch titled
Subject: kmsan: allow using __msan_instrument_asm_store() inside runtime
has been added to the -mm mm-unstable branch. Its filename is
kmsan-allow-using-__msan_instrument_asm_store-inside-runtime.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kmsan-allow-using-__msan_instrument_asm_store-inside-runtime.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Alexander Potapenko <glider@xxxxxxxxxx>
Subject: kmsan: allow using __msan_instrument_asm_store() inside runtime
Date: Mon, 28 Nov 2022 10:45:41 +0100
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@xxxxxxxxxx
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kmsan/instrumentation.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
--- a/mm/kmsan/instrumentation.c~kmsan-allow-using-__msan_instrument_asm_store-inside-runtime
+++ a/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 *a
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);
_
Patches currently in -mm which might be from glider@xxxxxxxxxx are
revert-kmsan-unpoison-tlb-in-arch_tlb_gather_mmu.patch
lockdep-allow-instrumenting-lockdepc-with-kmsan.patch
kmsan-allow-using-__msan_instrument_asm_store-inside-runtime.patch
