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From: Mark Rutland <mark.rutland@arm.com>
To: Peter Collingbourne <pcc@google.com>
Cc: Mark Brown <broonie@kernel.org>, Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Andrey Konovalov <andreyknvl@gmail.com>
Subject: Re: [PATCH v4 2/3] arm64: stacktrace: Relax frame record alignment requirement to 8 bytes
Date: Thu, 13 May 2021 10:16:33 +0100	[thread overview]
Message-ID: <20210513091633.GA10886@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20210513022709.983982-2-pcc@google.com>

Hi Peter,

On Wed, May 12, 2021 at 07:27:08PM -0700, Peter Collingbourne wrote:
> The AAPCS places no requirements on the alignment of the frame
> record. In theory it could be placed anywhere, although it seems
> sensible to require it to be aligned to 8 bytes. With an upcoming
> enhancement to tag-based KASAN Clang will begin creating frame records
> located at an address that is only aligned to 8 bytes. Accommodate
> such frame records in the stack unwinding code.
> 
> As pointed out by Mark Rutland, the userspace stack unwinding code
> has the same problem, so fix it there as well.
> 
> Signed-off-by: Peter Collingbourne <pcc@google.com>
> Link: https://linux-review.googlesource.com/id/Ia22c375230e67ca055e9e4bb639383567f7ad268
> Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Tested-by: Mark Rutland <mark.rutland@arm.com>
> ---
> v4:
> - rebase to 5.13rc1

I think the rebase went slightly wrong; note below.

> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 2fecbf152e80..020e575e5cd3 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -68,7 +68,11 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
>  	unsigned long fp = frame->fp;
>  	struct stack_info info;
>  
> -	if (fp & 0xf)
> +	/* Terminal record; nothing to unwind */
> +	if (!fp)
> +		return -ENOENT;
> +
> +	if (fp & 0x7)
>  		return -EINVAL;

The terminal record check got moved later in the function by commit:

  8533d5bfad41e74b ("arm64: stacktrace: restore terminal records")

... so this patch shouldn't re-add it. With that gone (and this just
changing the alignemnt check), this looks good to me.

Thanks,
Mark.

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  reply	other threads:[~2021-05-13  9:18 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-13  2:27 [PATCH v4 1/3] arm64: Change the on_*stack functions to take a size argument Peter Collingbourne
2021-05-13  2:27 ` [PATCH v4 2/3] arm64: stacktrace: Relax frame record alignment requirement to 8 bytes Peter Collingbourne
2021-05-13  9:16   ` Mark Rutland [this message]
2021-05-13 16:56     ` Peter Collingbourne
2021-05-13  2:27 ` [PATCH v4 3/3] kasan: arm64: support specialized outlined tag mismatch checks Peter Collingbourne

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