From: Karl Mehltretter <kmehltretter@gmail•com>
To: Russell King <linux@armlinux•org.uk>
Cc: Linus Walleij <linusw@kernel•org>,
"Russell King (Oracle)" <rmk+kernel@armlinux•org.uk>,
linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org, stable@vger•kernel.org,
Karl Mehltretter <kmehltretter@gmail•com>
Subject: [PATCH] ARM: entry: use byte load for KASAN VMAP stack shadow
Date: Fri, 22 May 2026 23:15:03 +0200 [thread overview]
Message-ID: <20260522211503.25219-1-kmehltretter@gmail.com> (raw)
Commit 44e9a3bb76e5 ("ARM: 9430/1: entry: Do a dummy read from
VMAP shadow") added a dummy read from the KASAN VMAP stack shadow in
__switch_to(). The read uses ldr, but KASAN shadow memory is
byte-granular and the computed shadow address is not guaranteed to be
word aligned.
Booting the QEMU versatilepb machine with an ARM926EJ-S CPU and
CONFIG_KASAN=y, CONFIG_KASAN_VMALLOC=y and CONFIG_VMAP_STACK=y faults
before init:
Unhandled fault: alignment exception (0x001) at 0xb91037f6
PC is at __switch_to+0x64/0x88
Use ldrb for the dummy shadow access. The code only needs to fault if
the shadow mapping is missing, so a byte load is sufficient and matches
the granularity of KASAN shadow memory.
Fixes: 44e9a3bb76e5 ("ARM: 9430/1: entry: Do a dummy read from VMAP shadow")
Cc: stable@vger•kernel.org # v6.13+
Assisted-by: Codex:gpt-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail•com>
---
arch/arm/kernel/entry-armv.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index ef6a657c8d13..a3d050ce9b79 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -567,7 +567,7 @@ ENTRY(__switch_to)
@ are using KASAN
mov_l r2, KASAN_SHADOW_OFFSET
add r2, r2, ip, lsr #KASAN_SHADOW_SCALE_SHIFT
- ldr r2, [r2]
+ ldrb r2, [r2]
#endif
#endif
--
2.39.5 (Apple Git-154)
next reply other threads:[~2026-05-22 21:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-22 21:15 Karl Mehltretter [this message]
2026-05-23 22:08 ` [PATCH] ARM: entry: use byte load for KASAN VMAP stack shadow Linus Walleij
2026-05-24 7:49 ` Karl Mehltretter
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