linux-kernel - [PATCH 1/2] instrumented.h: Add function instrument_write

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Message-ID: <20251106160845.1334274-4-aleksei.nikiforov@linux.ibm.com>
Date: Thu,  6 Nov 2025 17:08:46 +0100
From: Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
        Juergen Christ <jchrist@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>
Subject: [PATCH 1/2] instrumented.h: Add function instrument_write_after

clang generates call to __msan_instrument_asm_store with size calculated
based on inline asm constraints. It looks like there's no way to properly
write constraint for var-size memory write and make clang generate
__msan_instrument_asm_store call based on runtime-obtained size.

Implement instrument_write_after similar to instrument_write and
instrument_copy_from_user_after to manually fix kmsan behaviour
in such cases.

Signed-off-by: Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>
---
 include/linux/instrumented.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h
index 711a1f0d1a73..a498d914a8b0 100644
--- a/include/linux/instrumented.h
+++ b/include/linux/instrumented.h
@@ -41,6 +41,20 @@ static __always_inline void instrument_write(const volatile void *v, size_t size
 	kcsan_check_write(v, size);
 }
 
+/**
+ * instrument_write_after - instrument regular write access
+ * @v: address of access
+ * @size: size of access
+ *
+ * Instrument a regular write access. The instrumentation should be inserted
+ * after the actual write happens.
+ */
+static __always_inline void instrument_write_after(const volatile void *v,
+						   size_t size)
+{
+	kmsan_unpoison_memory((const void *)v, size);
+}
+
 /**
  * instrument_read_write - instrument regular read-write access
  * @v: address of access
-- 
2.43.7