On Tue, Sep 29, 2020 at 01:57:42PM -0700, Chang S. Bae wrote: > 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 I can't comment on the x86 specifics, but the approach followed in this series does seem consistent with the way arm64 populates AT_MINSIGSTKSZ. I need to dig up my glibc hacks for providing a sysconf interface to this... Cheers ---Dave > > [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 >
