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Re: [PATCH v4] aarch64: enforce >=64K guard size
- From: Florian Weimer <fw at deneb dot enyo dot de>
- To: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>, nd at arm dot com
- Date: Sat, 14 Jul 2018 16:02:27 +0200
- Subject: Re: [PATCH v4] aarch64: enforce >=64K guard size
- References: <firstname.lastname@example.org>
* 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.
Is there anything special in the aarch64 probing sequence that
*requires* that the guard is 64 KiB, or is it just that it is not
effective if it is not?