Re: [PATCH v4] aarch64: enforce >=64K guard size

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 12/07/18 10:06, Szabolcs Nagy wrote:
> previous discussion:
> https://sourceware.org/ml/libc-alpha/2018-01/msg00267.html
> i'd like to backport this to 2.28 if the gcc patches are accepted.
> 
> v4:
> - gcc patches are now under review:
> https://gcc.gnu.org/ml/gcc-patches/2018-07/msg00538.html
> https://gcc.gnu.org/ml/gcc-patches/2018-07/msg00542.html
> - update commit message (64K probing is the default abi).
> - add riscv, remove tile.
> - rebase.

ping.

gcc patches are committed at r264757

> v3:
> - more comment in allocate_stack.
> - define ARCH_MIN_GUARD_SIZE explicitly for all targets.
> - rebase on top of master.
> v2:
> - only change guard size on aarch64
> - don't report the inflated guard size
> 
> 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.
> 
> The patch does not affect threads with user allocated stacks.
> 
> 2018-07-12  Szabolcs Nagy  <szabolcs.nagy@arm.com>
> 
>     * nptl/allocatestack.c (allocate_stack): Use ARCH_MIN_GUARD_SIZE.
>     * sysdeps/aarch64/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/alpha/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/arm/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/hppa/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/i386/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/ia64/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/m68k/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/microblaze/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/mips/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/nios2/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/powerpc/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/riscv/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/s390/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/sh/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/sparc/sparc32/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/sparc/sparc64/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.
>     * sysdeps/x86_64/nptl/pthreaddef.h (ARCH_MIN_GUARD_SIZE): Define.