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

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Message-ID: <17de4426-8263-4ccb-8420-f6913d478ae9@arm.com>
Date: Tue, 1 Apr 2025 11:35:03 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Angelos Oikonomopoulos <angelos@...lia.com>,
 linux-arm-kernel@...ts.infradead.org
Cc: catalin.marinas@....com, 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 3/31/25 14:24, 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).
> 
> Signed-off-by: Angelos Oikonomopoulos <angelos@...lia.com>
> ---
>  arch/arm64/kernel/compat_alignment.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/compat_alignment.c b/arch/arm64/kernel/compat_alignment.c
> index deff21bfa680..b68e1d328d4c 100644
> --- a/arch/arm64/kernel/compat_alignment.c
> +++ b/arch/arm64/kernel/compat_alignment.c
> @@ -368,6 +368,8 @@ int do_compat_alignment_fixup(unsigned long addr, struct pt_regs *regs)
>  		return 1;
>  	}
>  
> +	if (!handler)
> +		return 1;

do_alignment_t32_to_handler() could return NULL, returning 1 seems to be
the right thing to do here and consistent. Otherwise does this cause a
kernel crash during subsequent call into handler() ?

>  	type = handler(addr, instr, regs);
>  
>  	if (type == TYPE_ERROR || type == TYPE_FAULT)