linux-kernel - Re: [PATCH] arm64: mops: Do not dereference src reg for a set operation

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Message-ID: <86zfh8ku5x.wl-maz@kernel.org>
Date: Wed, 26 Mar 2025 09:39:22 +0000
From: Marc Zyngier <maz@...nel.org>
To: Keir Fraser <keirf@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Kristina Martsenko <kristina.martsenko@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	Will Deacon <will@...nel.org>,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64: mops: Do not dereference src reg for a set operation

On Wed, 26 Mar 2025 07:02:55 +0000,
Keir Fraser <keirf@...gle.com> wrote:
> 
> The register is not defined and reading it can result in a UBSAN
> out-of-bounds array access error, specifically when the srcreg field
> value is 31.

Gah, XZR/SP encoding strikes back...

> 
> Cc: Kristina Martsenko <kristina.martsenko@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: stable@...r.kernel.org
> Signed-off-by: Keir Fraser <keirf@...gle.com>
> ---
>  arch/arm64/include/asm/traps.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
> index d780d1bd2eac..82cf1f879c61 100644
> --- a/arch/arm64/include/asm/traps.h
> +++ b/arch/arm64/include/asm/traps.h
> @@ -109,10 +109,9 @@ static inline void arm64_mops_reset_regs(struct user_pt_regs *regs, unsigned lon
>  	int dstreg = ESR_ELx_MOPS_ISS_DESTREG(esr);
>  	int srcreg = ESR_ELx_MOPS_ISS_SRCREG(esr);
>  	int sizereg = ESR_ELx_MOPS_ISS_SIZEREG(esr);
> -	unsigned long dst, src, size;
> +	unsigned long dst, size;
>  
>  	dst = regs->regs[dstreg];
> -	src = regs->regs[srcreg];
>  	size = regs->regs[sizereg];
>  
>  	/*
> @@ -129,6 +128,7 @@ static inline void arm64_mops_reset_regs(struct user_pt_regs *regs, unsigned lon
>  		}
>  	} else {
>  		/* CPY* instruction */
> +		unsigned long src = regs->regs[srcreg];
>  		if (!(option_a ^ wrong_option)) {
>  			/* Format is from Option B */
>  			if (regs->pstate & PSR_N_BIT) {

Reviewed-by: Marc Zyngier <maz@...nel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.