linux-kernel - Re: [PATCH] arm64: Don't call NULL in do_compat_alignment

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Message-ID: <Z-bzOrF-4lSykkgJ@arm.com>
Date: Fri, 28 Mar 2025 19:06:34 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Angelos Oikonomopoulos <angelos@...lia.com>
Cc: linux-arm-kernel@...ts.infradead.org, will@...nel.org,
	linux-kernel@...r.kernel.org, kernel-dev@...lia.com
Subject: Re: [PATCH] arm64: Don't call NULL in do_compat_alignment_fixup

On Wed, Mar 26, 2025 at 02:35:21PM +0100, Angelos Oikonomopoulos wrote:
> do_alignment_t32_to_handler only fixes up alignment faults for specific
> instructions; it returns NULL otherwise. When that's the case, signal to
> the caller that it needs to proceed with the regular alignment fault
> handling (i.e. SIGBUS).

Did you hit this in practice? Which instruction triggered the alignment
fault that was not handled by do_alignment_t32_to_handler()? Standard
LDR/STR should not trigger unaligned accesses unless you have some
device memory mapped in user space.

> Signed-off-by: Angelos Oikonomopoulos <angelos@...lia.com>
> ---
>  arch/arm64/kernel/compat_alignment.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/compat_alignment.c b/arch/arm64/kernel/compat_alignment.c
> index deff21bfa680..76cf1c1b5bc6 100644
> --- a/arch/arm64/kernel/compat_alignment.c
> +++ b/arch/arm64/kernel/compat_alignment.c
> @@ -34,7 +34,7 @@
>  
>  #define REGMASK_BITS(i)	(i & 0xffff)
>  
> -#define BAD_INSTR 	0xdeadc0de
> +#define BAD_INSTR	0xdeadc0de

Unrelated change (white space I guess), please drop it, not worth
fixing.

-- 
Catalin