On 06/21, Oleg Nesterov wrote:
>
> On 06/21, Cyrill Gorcunov wrote:
> >
> > On Wed, Jun 21, 2017 at 05:57:30PM +0200, Oleg Nesterov wrote:
> > > >
> > > > p = fake_grow_down;
> > > > *p-- = 'c';
> > >
> > > I guess this works? I mean, *p-- = 'c' should not fail...
> >
> > It fails.
>
> Hmm. Impossible ;) could you add the additional printf's to re-check?
Yes, please...
> > p = fake_grow_down;
> > *p-- = 'c';
>
> once again, I can't believe this STORE can fail...
>
> > *p = 'b';
>
> Ah. I forgot about another kernel "feature" ;) not related to the recent guard
> page changes...
On the second thought it is actually connected, and it seems we really need to
remove this code in do_page_fault... I'll re-check tomorrow, need to run away.
> Could you test the patch below?
>
> Oleg.
>
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8ad91a0..edc5d68 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1416,7 +1416,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long
> error_code,
> * and pusha to work. ("enter $65535, $31" pushes
> * 32 pointers and then decrements %sp by 65535.)
> */
> - if (unlikely(address + 65536 + 32 * sizeof(unsigned long) <
> regs->sp)) {
> +if (0) if (unlikely(address + 65536 + 32 * sizeof(unsigned
> long) < regs->sp)) {
> bad_area(regs, error_code, address);
> return;
> }
