linux-kernel - [PATCH AUTOSEL 6.10 092/121] x86/kmsan: Fix hook for unaligned accesses

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Message-ID: <20240801000834.3930818-92-sashal@kernel.org>
Date: Wed, 31 Jul 2024 20:00:30 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Brian Johannesmeyer <bjohannesmeyer@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sashal@...nel.org>,
	tglx@...utronix.de,
	mingo@...hat.com,
	dave.hansen@...ux.intel.com,
	x86@...nel.org
Subject: [PATCH AUTOSEL 6.10 092/121] x86/kmsan: Fix hook for unaligned accesses

From: Brian Johannesmeyer <bjohannesmeyer@...il.com>

[ Upstream commit bf6ab33d8487f5e2a0998ce75286eae65bb0a6d6 ]

When called with a 'from' that is not 4-byte-aligned, string_memcpy_fromio()
calls the movs() macro to copy the first few bytes, so that 'from' becomes
4-byte-aligned before calling rep_movs(). This movs() macro modifies 'to', and
the subsequent line modifies 'n'.

As a result, on unaligned accesses, kmsan_unpoison_memory() uses the updated
(aligned) values of 'to' and 'n'. Hence, it does not unpoison the entire
region.

Save the original values of 'to' and 'n', and pass those to
kmsan_unpoison_memory(), so that the entire region is unpoisoned.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@...il.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Alexander Potapenko <glider@...gle.com>
Link: https://lore.kernel.org/r/20240523215029.4160518-1-bjohannesmeyer@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/lib/iomem.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c
index e0411a3774d49..5eecb45d05d5d 100644
--- a/arch/x86/lib/iomem.c
+++ b/arch/x86/lib/iomem.c
@@ -25,6 +25,9 @@ static __always_inline void rep_movs(void *to, const void *from, size_t n)
 
 static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
 {
+	const void *orig_to = to;
+	const size_t orig_n = n;
+
 	if (unlikely(!n))
 		return;
 
@@ -39,7 +42,7 @@ static void string_memcpy_fromio(void *to, const volatile void __iomem *from, si
 	}
 	rep_movs(to, (const void *)from, n);
 	/* KMSAN must treat values read from devices as initialized. */
-	kmsan_unpoison_memory(to, n);
+	kmsan_unpoison_memory(orig_to, orig_n);
 }
 
 static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
-- 
2.43.0