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From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: tglx@linutronix.de, mingo@kernel.org, bp@suse.de,
	luto@kernel.org, x86@kernel.org
Cc: len.brown@intel.com, dave.hansen@intel.com, hjl.tools@gmail.com,
	Dave.Martin@arm.com, mpe@ellerman.id.au, tony.luck@intel.com,
	ravi.v.shankar@intel.com, libc-alpha@sourceware.org,
	linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org, chang.seok.bae@intel.com
Subject: [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size
Date: Tue, 29 Sep 2020 13:57:42 -0700
Message-ID: <20200929205746.6763-1-chang.seok.bae@intel.com> (raw)

During signal entry, the kernel pushes data onto the normal userspace
stack. On x86, the data pushed onto the user stack includes XSAVE state,
which has grown over time as new features and larger registers have been
added to the architecture.

MINSIGSTKSZ is a constant provided in the kernel signal.h headers and
typically distributed in lib-dev(el) packages, e.g. [1]. Its value is
compiled into programs and is part of the user/kernel ABI. The MINSIGSTKSZ
constant indicates to userspace how much data the kernel expects to push on
the user stack, [2][3].

However, this constant is much too small and does not reflect recent
additions to the architecture. For instance, when AVX-512 states are in
use, the signal frame size can be 3.5KB while MINSIGSTKSZ remains 2KB.

The bug report [4] explains this as an ABI issue. The small MINSIGSTKSZ can
cause user stack overflow when delivering a signal.

In this series, we suggest a couple of things:
1. Provide a variable minimum stack size to userspace, as a similar
   approach to [5]
2. Avoid using a too-small alternate stack

[1]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/bits/sigstack.h;h=b9dca794da093dc4d41d39db9851d444e1b54d9b;hb=HEAD
[2]: https://www.gnu.org/software/libc/manual/html_node/Signal-Stack.html
[3]: https://man7.org/linux/man-pages/man2/sigaltstack.2.html
[4]: https://bugzilla.kernel.org/show_bug.cgi?id=153531
[5]: https://blog.linuxplumbersconf.org/2017/ocw/system/presentations/4671/original/plumbers-dm-2017.pdf

Chang S. Bae (4):
  x86/signal: Introduce helpers to get the maximum signal frame size
  x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ
  x86/signal: Prevent an alternate stack overflow before a signal
    delivery
  selftest/x86/signal: Include test cases for validating sigaltstack

 arch/x86/ia32/ia32_signal.c               |  11 +-
 arch/x86/include/asm/elf.h                |   4 +
 arch/x86/include/asm/fpu/signal.h         |   2 +
 arch/x86/include/asm/sigframe.h           |  25 +++++
 arch/x86/include/uapi/asm/auxvec.h        |   6 +-
 arch/x86/kernel/cpu/common.c              |   3 +
 arch/x86/kernel/fpu/signal.c              |  20 ++++
 arch/x86/kernel/signal.c                  |  66 +++++++++++-
 tools/testing/selftests/x86/Makefile      |   2 +-
 tools/testing/selftests/x86/sigaltstack.c | 126 ++++++++++++++++++++++
 10 files changed, 258 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/x86/sigaltstack.c

--
2.17.1


             reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-29 20:57 Chang S. Bae [this message]
2020-09-29 20:57 ` [RFC PATCH 1/4] x86/signal: Introduce helpers to get the maximum signal frame size Chang S. Bae
2020-10-05 13:42   ` Dave Martin
2020-10-06 17:45     ` Bae, Chang Seok
2020-10-07 10:05       ` Dave Martin
2020-10-08 22:43         ` Bae, Chang Seok
2020-10-12 13:26           ` Dave Martin
2020-09-29 20:57 ` [RFC PATCH 2/4] x86/elf: Support a new ELF aux vector AT_MINSIGSTKSZ Chang S. Bae
2020-09-29 20:57 ` [RFC PATCH 3/4] x86/signal: Prevent an alternate stack overflow before a signal delivery Chang S. Bae
2020-09-29 20:57 ` [RFC PATCH 4/4] selftest/x86/signal: Include test cases for validating sigaltstack Chang S. Bae
2020-10-05 13:45 ` [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size Dave Martin
2020-10-05 21:17   ` H.J. Lu
2020-10-06  9:25     ` Dave Martin
2020-10-06 12:12       ` H.J. Lu
2020-10-06 15:18         ` H.J. Lu
2020-10-06 15:43           ` Dave Martin
2020-10-06 16:52             ` H.J. Lu
2020-10-06 15:25         ` Dave Martin
2020-10-06 15:33           ` Dave Hansen
2020-10-06 17:00             ` Dave Martin
2020-10-06 18:21               ` Florian Weimer
2020-10-07 10:19                 ` Dave Martin
2020-10-06 18:30               ` Dave Hansen
2020-10-07 10:20                 ` Dave Martin
2020-10-06 15:34           ` H.J. Lu
2020-10-06 16:55             ` Dave Martin
2020-10-06 17:44               ` H.J. Lu
2020-10-07 10:47                 ` Dave Martin
2020-10-07 13:30                   ` H.J. Lu
2020-10-07 15:45                     ` Dave Martin
2020-10-07 17:43                       ` H.J. Lu

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