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[v5,0/2] arm64: signal: Report signal frame size to userspace via auxv

Message ID 1527261428-6662-1-git-send-email-Dave.Martin@arm.com
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Series arm64: signal: Report signal frame size to userspace via auxv | expand

Message

Dave Martin May 25, 2018, 3:17 p.m. UTC 
This series adds support for telling userspace the size of the signal
frame via a new AT_MINSIGSTKSZ entry in the aux vector.

This is an update to [1].  Changes are minor.  The main difference is
that no attempt is made to give userspace a sensible AT_MINSIGSTKSZ if
initialisation goes wrong, since this is indicative of a kernel bug
anyway.

See individual patches for the delta.

[1] [PATCH v4 0/2] arm64: signal: Report signal frame size to userspace via auxv
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/580284.html


Dave Martin (2):
  arm64/sve: Thin out initialisation sanity-checks for sve_max_vl
  arm64: signal: Report signal frame size to userspace via auxv

 arch/arm64/include/asm/elf.h         | 11 ++++++++
 arch/arm64/include/asm/processor.h   |  5 ++++
 arch/arm64/include/uapi/asm/auxvec.h |  3 ++-
 arch/arm64/kernel/cpufeature.c       |  1 +
 arch/arm64/kernel/fpsimd.c           | 17 +++---------
 arch/arm64/kernel/ptrace.c           |  3 ---
 arch/arm64/kernel/signal.c           | 52 +++++++++++++++++++++++++++++++-----
 7 files changed, 68 insertions(+), 24 deletions(-)

Comments

Will Deacon May 25, 2018, 3:20 p.m. UTC | #1 
On Fri, May 25, 2018 at 04:17:08PM +0100, Dave Martin wrote:
> Stateful CPU architecture extensions may require the signal frame
> to grow to a size that exceeds the arch's MINSIGSTKSZ #define.
> However, changing this #define is an ABI break.
> 
> To allow userspace the option of determining the signal frame size
> in a more forwards-compatible way, this patch adds a new auxv entry
> tagged with AT_MINSIGSTKSZ, which provides the maximum signal frame
> size that the process can observe during its lifetime.
> 
> If AT_MINSIGSTKSZ is absent from the aux vector, the caller can
> assume that the MINSIGSTKSZ #define is sufficient.  This allows for
> a consistent interface with older kernels that do not provide
> AT_MINSIGSTKSZ.
> 
> The idea is that libc could expose this via sysconf() or some
> similar mechanism.
> 
> There is deliberately no AT_SIGSTKSZ.  The kernel knows nothing
> about userspace's own stack overheads and should not pretend to
> know.

Thanks, Dave.

Acked-by: Will Deacon <will.deacon@arm.com>

Will