linux-kernel - Re: [PATCH 2/4] x86: Fix the hw

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Date:	Sun, 24 Nov 2013 14:40:57 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/4] x86: Fix the hw_breakpoint range check

On Sun, Nov 24, 2013 at 11:32:49AM +0100, Frederic Weisbecker wrote:
> From: Oleg Nesterov <oleg@...hat.com>
> 
> arch_check_bp_in_kernelspace() tries to avoid the overflow and does 2
> TASK_SIZE checks but it needs OR, not AND. Consider va = TASK_SIZE -1
> and len = 2 case.
> 
> Note: TASK_SIZE doesn't look right at least on x86, I think it should
> be replaced by TASK_SIZE_MAX.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Fixes: 0067f1297241ea567f2b22a455519752d70fcca9
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  arch/x86/kernel/hw_breakpoint.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
> index f66ff16..1131c1f 100644
> --- a/arch/x86/kernel/hw_breakpoint.c
> +++ b/arch/x86/kernel/hw_breakpoint.c
> @@ -200,7 +200,7 @@ int arch_check_bp_in_kernelspace(struct perf_event *bp)
>  	va = info->address;
>  	len = get_hbp_len(info->len);
>  
> -	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
> +	return (va >= TASK_SIZE) || ((va + len - 1) >= TASK_SIZE);

Well, can't you simplify it even further?

	return (va + len - 1) >= TASK_SIZE;

AFAICT, the high end of the range matters, no?

Unless the original code was meant to short-circuit at the first
comparison already...

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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