Re: [PATCH v3 05/17] arm64, hibernate: check pgd table allocation

[Pavel Tatashin]

On Fri, Sep 6, 2019 at 11:17 AM James Morse <james.morse@xxxxxxx> wrote:
>
> Hi Pavel,
>
> On 21/08/2019 19:31, Pavel Tatashin wrote:
> > There is a bug in create_safe_exec_page(), when page table is allocated
> > it is not checked that table is allocated successfully:
> >
> > But it is dereferenced in: pgd_none(READ_ONCE(*pgdp)).
>
> If there is a bug, it shouldn't be fixed part way through a series. This makes it
> difficult to backport the fix.
>
> Please split this out as an independent patch with a 'Fixes:' tag for the commit that
> introduced the bug.
>
>
> > Another issue,
>
> So this patch does two things? That is rarely a good idea. Again, this makes it difficult
> to backport the fix.
>
>
> > is that phys_to_ttbr() uses an offset in page table instead
> > of pgd directly.
>
> If you were going to reuse this, that would be a bug. But because the only page that is
> being mapped, is mapped to PAGE_SIZE, all the top bits will be 0. The offset calls are
> boiler-plate. It doesn't look intentional, but its harmless.

Yes, it is harmless otherwise the code would not work. But it is
confusing to read, and looks broken. I will separate this change as
two patches as you suggested.

Thank you,
Pasha