linux-kernel - Re: [RFC PATCH 1/5] x86: add user_mode_vm check in stack_overflow

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Date:	Thu, 10 Nov 2011 14:52:03 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Randy Dunlap <rdunlap@...otime.net>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH 1/5] x86: add user_mode_vm check in
 stack_overflow_check

On Mon, Nov 07, 2011 at 02:52:35PM +0900, Mitsuo Hayasaka wrote:
> The kernel stack overflow is checked in stack_overflow_check(),
> which may wrongly detect the overflow if the stack pointer
> pointed to the kernel stack accidentally.

I think you mean to say 'points'.

How do we accidently point the stack pointer to the kernel stack?

> 
> This patch adds user-mode-vm checking before it to avoid this
> misdetection and bails out early if the user stack is used.
> 
> Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> ---
> 
>  arch/x86/kernel/irq_64.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
> index acf8fbf..69bca46 100644
> --- a/arch/x86/kernel/irq_64.c
> +++ b/arch/x86/kernel/irq_64.c
> @@ -38,6 +38,9 @@ static inline void stack_overflow_check(struct pt_regs *regs)
>  #ifdef CONFIG_DEBUG_STACKOVERFLOW
>  	u64 curbase = (u64)task_stack_page(current);
>  
> +	if (user_mode_vm(regs))
> +		return;
> +
>  	WARN_ONCE(regs->sp >= curbase &&
>  		  regs->sp <= curbase + THREAD_SIZE &&
>  		  regs->sp <  curbase + sizeof(struct thread_info) +
> 
> --
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