* [PATCH] ARM: io: avoid KASAN instrumentation of raw halfword I/O
@ 2026-05-22 21:20 Karl Mehltretter
2026-05-23 22:11 ` Linus Walleij
0 siblings, 1 reply; 3+ messages in thread
From: Karl Mehltretter @ 2026-05-22 21:20 UTC (permalink / raw)
To: Russell King
Cc: Abbott Liu, Linus Walleij, Ard Biesheuvel, Florian Fainelli,
linux-arm-kernel, linux-kernel, stable, Karl Mehltretter
Commit 421015713b30 ("ARM: 9017/2: Enable KASan for ARM") made KASAN
instrument ARM C memory accesses. For CPUs before ARMv6, __raw_readw()
and __raw_writew() are C volatile halfword accesses, so KASAN instruments
them as normal memory accesses.
That is not valid for MMIO. On the QEMU versatilepb machine with an
ARM926EJ-S CPU and CONFIG_KASAN=y, PL011 probing traps while registering
the UART:
Unable to handle kernel paging request at virtual address bd23e207
PC is at __asan_store2+0x2c/0x9c
LR is at pl011_register_port+0x4c/0x19c
Keep the existing volatile halfword access, but move the pre-ARMv6
definitions into __no_kasan_or_inline functions so raw MMIO halfword
accesses are not instrumented by KASAN. The ARMv6-and-newer inline
assembly path is unchanged.
Fixes: 421015713b30 ("ARM: 9017/2: Enable KASan for ARM")
Cc: stable@vger•kernel.org # v5.11+
Assisted-by: Codex:gpt-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail•com>
---
arch/arm/include/asm/io.h | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
index bae5edf348ef..e6bd9e79737c 100644
--- a/arch/arm/include/asm/io.h
+++ b/arch/arm/include/asm/io.h
@@ -56,8 +56,19 @@ void __raw_readsl(const volatile void __iomem *addr, void *data, int longlen);
* the bus. Rather than special-case the machine, just let the compiler
* generate the access for CPUs prior to ARMv6.
*/
-#define __raw_readw(a) (__chk_io_ptr(a), *(volatile unsigned short __force *)(a))
-#define __raw_writew(v,a) ((void)(__chk_io_ptr(a), *(volatile unsigned short __force *)(a) = (v)))
+#define __raw_writew __raw_writew
+static __no_kasan_or_inline void __raw_writew(u16 val, volatile void __iomem *addr)
+{
+ __chk_io_ptr(addr);
+ *(volatile unsigned short __force *)addr = val;
+}
+
+#define __raw_readw __raw_readw
+static __no_kasan_or_inline u16 __raw_readw(const volatile void __iomem *addr)
+{
+ __chk_io_ptr(addr);
+ return *(const volatile unsigned short __force *)addr;
+}
#else
/*
* When running under a hypervisor, we want to avoid I/O accesses with
--
2.39.5 (Apple Git-154)
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] ARM: io: avoid KASAN instrumentation of raw halfword I/O
2026-05-22 21:20 [PATCH] ARM: io: avoid KASAN instrumentation of raw halfword I/O Karl Mehltretter
@ 2026-05-23 22:11 ` Linus Walleij
2026-05-24 8:09 ` Karl Mehltretter
0 siblings, 1 reply; 3+ messages in thread
From: Linus Walleij @ 2026-05-23 22:11 UTC (permalink / raw)
To: Karl Mehltretter
Cc: Russell King, Abbott Liu, Ard Biesheuvel, Florian Fainelli,
linux-arm-kernel, linux-kernel, stable
On Fri, May 22, 2026 at 11:20 PM Karl Mehltretter
<kmehltretter@gmail•com> wrote:
> Commit 421015713b30 ("ARM: 9017/2: Enable KASan for ARM") made KASAN
> instrument ARM C memory accesses. For CPUs before ARMv6, __raw_readw()
> and __raw_writew() are C volatile halfword accesses, so KASAN instruments
> them as normal memory accesses.
>
> That is not valid for MMIO. On the QEMU versatilepb machine with an
> ARM926EJ-S CPU and CONFIG_KASAN=y, PL011 probing traps while registering
> the UART:
>
> Unable to handle kernel paging request at virtual address bd23e207
> PC is at __asan_store2+0x2c/0x9c
> LR is at pl011_register_port+0x4c/0x19c
>
> Keep the existing volatile halfword access, but move the pre-ARMv6
> definitions into __no_kasan_or_inline functions so raw MMIO halfword
> accesses are not instrumented by KASAN. The ARMv6-and-newer inline
> assembly path is unchanged.
>
> Fixes: 421015713b30 ("ARM: 9017/2: Enable KASan for ARM")
> Cc: stable@vger•kernel.org # v5.11+
> Assisted-by: Codex:gpt-5
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail•com>
That makes sense.
Reviewed-by: Linus Walleij <linusw@kernel•org>
Please put this patch into Russell's patch tracker.
Yours,
Linus Walleij
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] ARM: io: avoid KASAN instrumentation of raw halfword I/O
2026-05-23 22:11 ` Linus Walleij
@ 2026-05-24 8:09 ` Karl Mehltretter
0 siblings, 0 replies; 3+ messages in thread
From: Karl Mehltretter @ 2026-05-24 8:09 UTC (permalink / raw)
To: Linus Walleij
Cc: Russell King, Abbott Liu, Ard Biesheuvel, Florian Fainelli,
linux-arm-kernel, linux-kernel, stable
On Sun, May 24, 2026 at 12:11:36AM +0100, Linus Walleij wrote:
> Please put this patch into Russell's patch tracker.
Done: https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9474/1
Thanks,
Karl
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-05-22 21:20 [PATCH] ARM: io: avoid KASAN instrumentation of raw halfword I/O Karl Mehltretter
2026-05-23 22:11 ` Linus Walleij
2026-05-24 8:09 ` Karl Mehltretter
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