[PATCH] x86/traps: do not hash pointers in handle_stack_overflow()

[PATCH] x86/traps: do not hash pointers in handle_stack_overflow()

[Eric Dumazet]

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)
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",
 		 (void *)fault_address, current->stack,
 		 (char *)current->stack + THREAD_SIZE - 1);
 	die(message, regs, 0);
-- 
2.25.0.341.g760bfbb309-goog

Re: [PATCH] x86/traps: do not hash pointers in handle_stack_overflow()

[Thomas Gleixner]

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.

> 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() ?

Thanks,

        tglx

Re: [PATCH] x86/traps: do not hash pointers in handle_stack_overflow()

[Eric Dumazet]

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.