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References: <20200207043836.106657-1-edumazet@google.com> <87tv42xxr5.fsf@nanos.tec.linutronix.de>
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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 7 Feb 2020 07:18:18 -0800
Message-ID: <CANn89i+mo08vK3ejvmn7DxvHEkAox4Xpm9Dm5hGc=9-+Xwxi4g@mail.gmail.com>
Subject: Re: [PATCH] x86/traps: do not hash pointers in handle_stack_overflow()
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Andy Lutomirski <luto@kernel.org>
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On Fri, Feb 7, 2020 at 6:44 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Eric Dumazet <edumazet@google.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.

Unfortunately this KASAN report has no repro yet. I have no idea what
triggered the fault ;)

>
> > 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@google.com>
> > Cc: Andy Lutomirski <luto@kernel.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() ?
>


Sure I will, thanks.