linux-kernel - Re: [PATCH v2 08/18] x86/dumpstack: Handle stack overflow on all stacks

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Date:   Thu, 23 Nov 2017 12:19:21 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v2 08/18] x86/dumpstack: Handle stack overflow on all
 stacks

On Tue, Nov 21, 2017 at 08:44:03PM -0800, Andy Lutomirski wrote:
> We currently special-case stack overflow on the task stack.  We're
> going to start putting special stacks in the fixmap with a custom
> layout, so they'll have guard pages, too.  Teach the unwinder to be
> able to unwind an overflow of any of the stacks.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/kernel/dumpstack.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 5e7d10e8ca25..635dcbfe2398 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -90,24 +90,30 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
>  	 * - task stack
>  	 * - interrupt stack
>  	 * - HW exception stacks (double fault, nmi, debug, mce)
> +	 * - SYSENTER stack
>  	 *
> -	 * x86-32 can have up to three stacks:
> +	 * x86-32 can have up to four stacks:
>  	 * - task stack
>  	 * - softirq stack
>  	 * - hardirq stack
> +	 * - SYSENTER stack
>  	 */
>  	for (regs = NULL; stack; stack = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
>  		const char *stack_name;
>  
> -		/*
> -		 * If we overflowed the task stack into a guard page, jump back
> -		 * to the bottom of the usable stack.
> -		 */
> -		if (task_stack_page(task) - (void *)stack < PAGE_SIZE)
> -			stack = task_stack_page(task);
> -
> -		if (get_stack_info(stack, task, &stack_info, &visit_mask))
> -			break;
> +		if (get_stack_info(stack, task, &stack_info, &visit_mask)) {
> +			/*
> +			 * We weren't on a valid stack.  It's possible that
> +			 * we overflowed a valid stack into a guard page.
> +			 * See if the next page up is valid to that we can

s/to/so/

> +			 * generate some kind of backtrace if this happens.
> +			 */
> +			stack = (unsigned long *)
> +				PAGE_ALIGN((unsigned long)stack);
> +			if (get_stack_info(stack, task, &stack_info,
> +					   &visit_mask))

Yeah, let them stick out.

With that:

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--