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ARM: 9475/1: entry: use byte load for KASAN VMAP stack shadow

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Commit 44e9a3bb76 ("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 the KASAN shadow address is
byte-granular and is not guaranteed to be word aligned.

ARMv5 faults unaligned word loads. With CONFIG_KASAN_VMALLOC and
CONFIG_VMAP_STACK enabled, ARM926/VersatilePB crashes in __switch_to()
with an alignment exception before reaching init.

Use ldrb for the dummy shadow access. The code only needs to fault in the
shadow mapping if the stack shadow is missing, so a byte load is sufficient
and matches the granularity of KASAN shadow memory.

Fixes: 44e9a3bb76 ("ARM: 9430/1: entry: Do a dummy read from VMAP shadow")
Cc: stable@vger.kernel.org # v6.13+
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Karl Mehltretter 2026-05-24 06:52:35 +01:00 committed by Russell King
parent d59ed80371
commit 77a1f6883d
1 changed files with 1 additions and 1 deletions
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2
arch/arm/kernel/entry-armv.S
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@ -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