Re: [PATCH v5] aarch64: enforce >=64K guard size

[Florian Weimer <fweimer@redhat.com>]

* Szabolcs Nagy:

> There are several compiler implementations that allow large stack
> allocations to jump over the guard page at the end of the stack and
> corrupt memory beyond that. See CVE-2017-1000364.
>
> Compilers can emit code to probe the stack such that the guard page
> cannot be skipped, but on aarch64 the probe interval is 64K by default
> instead of the minimum supported page size (4K).
>
> This patch enforces at least 64K guard on aarch64 unless the guard
> is disabled by setting its size to 0.  For backward compatibility
> reasons the increased guard is not reported, so it is only observable
> by exhausting the address space or parsing /proc/self/maps on linux.
>
> On other targets the patch has no effect. If the stack probe interval
> is larger than a page size on a target then ARCH_MIN_GUARD_SIZE can
> be defined to get large enough stack guard on libc allocated stacks.
>
> The patch does not affect threads with user allocated stacks.

I think this is okay.  I checked that all architectures still build.
I filed bug 26691 to help with tracking the backports.  Would you please
reference this bug in your commit message?

Thanks,
Florian
-- 
Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill