On Mon, Oct 5, 2020 at 6:45 AM Dave Martin <Dave.Martin@xxxxxxx> wrote: > > 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... Here is my proposal for glibc: https://sourceware.org/pipermail/libc-alpha/2020-September/118098.html 1. Define SIGSTKSZ and MINSIGSTKSZ to 64KB. 2. Add _SC_RSVD_SIG_STACK_SIZE for signal stack size reserved by the kernel. 3. Deprecate SIGSTKSZ and MINSIGSTKSZ if _SC_RSVD_SIG_STACK_SIZE is in use. -- H.J.
