linux-kernel - Re: [PATCH] x86/traps: do not hash pointers in handle_stack

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Message-ID: <87tv42xxr5.fsf@nanos.tec.linutronix.de>
Date:   Fri, 07 Feb 2020 14:44:46 +0000
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Eric Dumazet <edumazet@...gle.com>, Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] x86/traps: do not hash pointers in handle_stack_overflow()

Eric Dumazet <edumazet@...gle.com> writes:

> Mangling stack pointers in handle_stack_overflow() is moot,
> as registers (including RSP/RBP) are clear anyway.
>
> BUG: stack guard page was hit at 0000000063381e80 (stack is
> 000000008edc5696..0000000012256c50)

To illustrate your argument above it would be useful to provide the post
patch output as well.

> kernel stack overflow (double-fault): 0000 [#1] PREEMPT SMP KASAN
> ...
> RSP: 0018:ffffc90002c1ffc0 EFLAGS: 00010802
> RAX: 1ffff11004a0094c RBX: ffff888025004180 RCX: c9d82d1007bb146c
> RDX: dffffc0000000000 RSI: ffff888025004a40 RDI: ffff888025004180
> RBP: ffffc90002c201c0 R08: dffffc0000000000 R09: fffffbfff1405915
> R10: fffffbfff1405915 R11: 0000000000000000 R12: ffff888025004a60
> R13: ffff888025004a10 R14: c9d82d1007bb146c R15: ffff888025004180
> ...
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/kernel/traps.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 6ef00eb6fbb925e86109f86845e2b3ccef4023ec..44873df292bd3f9f77bb721c53cb8a1c40994cca 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -296,7 +296,7 @@ __visible void __noreturn handle_stack_overflow(const char *message,
>  						struct pt_regs *regs,
>  						unsigned long fault_address)
>  {
> -	printk(KERN_EMERG "BUG: stack guard page was hit at %p (stack is %p..%p)\n",
> +	printk(KERN_EMERG "BUG: stack guard page was hit at %px (stack
> is %px..%px)\n",

While touching this, can you please switch it to pr_emerg() ?

Thanks,

        tglx