lkml.org 
[lkml]   [2021]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[patch V2 1/8] selftests/x86: Test signal frame XSTATE header corruption handling
    Date
    From: Andy Lutomirski <luto@kernel.org>

    This is very heavily based on some code from Thomas Gleixner. On a system
    without XSAVES, it triggers the WARN_ON():

    Bad FPU state detected at copy_kernel_to_fpregs+0x2f/0x40, reinitializing FPU registers.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    V2: main() -> main(void) (Borislav)
    ---
    tools/testing/selftests/x86/Makefile | 3
    tools/testing/selftests/x86/corrupt_xstate_header.c | 114 ++++++++++++++++++++
    2 files changed, 116 insertions(+), 1 deletion(-)
    create mode 100644 tools/testing/selftests/x86/corrupt_xstate_header.c

    --- a/tools/testing/selftests/x86/Makefile
    +++ b/tools/testing/selftests/x86/Makefile
    @@ -17,7 +17,8 @@ TARGETS_C_BOTHBITS := single_step_syscal
    TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \
    test_FCMOV test_FCOMI test_FISTTP \
    vdso_restorer
    -TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering
    +TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
    + corrupt_xstate_header
    # Some selftests require 32bit support enabled also on 64bit systems
    TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall

    --- /dev/null
    +++ b/tools/testing/selftests/x86/corrupt_xstate_header.c
    @@ -0,0 +1,114 @@
    +// SPDX-License-Identifier: GPL-2.0-only
    +/*
    + * Corrupt the XSTATE header in a signal frame
    + *
    + * Based on analysis and a test case from Thomas Gleixner.
    + */
    +
    +#define _GNU_SOURCE
    +
    +#include <stdlib.h>
    +#include <stdio.h>
    +#include <string.h>
    +#include <sched.h>
    +#include <signal.h>
    +#include <err.h>
    +#include <unistd.h>
    +#include <stdint.h>
    +#include <sys/wait.h>
    +
    +static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
    + unsigned int *ecx, unsigned int *edx)
    +{
    + asm volatile(
    + "cpuid;"
    + : "=a" (*eax),
    + "=b" (*ebx),
    + "=c" (*ecx),
    + "=d" (*edx)
    + : "0" (*eax), "2" (*ecx));
    +}
    +
    +static inline int xsave_enabled(void)
    +{
    + unsigned int eax, ebx, ecx, edx;
    +
    + eax = 0x1;
    + ecx = 0x0;
    + __cpuid(&eax, &ebx, &ecx, &edx);
    +
    + /* Is CR4.OSXSAVE enabled ? */
    + return ecx & (1U << 27);
    +}
    +
    +static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
    + int flags)
    +{
    + struct sigaction sa;
    +
    + memset(&sa, 0, sizeof(sa));
    + sa.sa_sigaction = handler;
    + sa.sa_flags = SA_SIGINFO | flags;
    + sigemptyset(&sa.sa_mask);
    + if (sigaction(sig, &sa, 0))
    + err(1, "sigaction");
    +}
    +
    +static void sigusr1(int sig, siginfo_t *info, void *uc_void)
    +{
    + ucontext_t *uc = uc_void;
    + uint8_t *fpstate = (uint8_t *)uc->uc_mcontext.fpregs;
    + uint64_t *xfeatures = (uint64_t *)(fpstate + 512);
    +
    + printf("\tWreckage XSTATE header\n");
    + /* Wreckage the first reserved byte in the header */
    + *(xfeatures + 2) = 0xfffffff;
    +}
    +
    +static void sigsegv(int sig, siginfo_t *info, void *uc_void)
    +{
    + printf("\tGot SIGSEGV\n");
    +}
    +
    +int main()
    +{
    + cpu_set_t set;
    +
    + sethandler(SIGUSR1, sigusr1, 0);
    + sethandler(SIGSEGV, sigsegv, 0);
    +
    + if (!xsave_enabled()) {
    + printf("[SKIP] CR4.OSXSAVE disabled.\n");
    + return 0;
    + }
    +
    + CPU_ZERO(&set);
    + CPU_SET(0, &set);
    +
    + /*
    + * Enforce that the child runs on the same CPU
    + * which in turn forces a schedule.
    + */
    + sched_setaffinity(getpid(), sizeof(set), &set);
    +
    + printf("[RUN]\tSend ourselves a signal\n");
    + raise(SIGUSR1);
    +
    + printf("[OK]\tBack from the signal. Now schedule.\n");
    + pid_t child = fork();
    + if (child < 0)
    + err(1, "fork");
    + if (child == 0)
    + return 0;
    + if (child)
    + waitpid(child, NULL, 0);
    + printf("[OK]\tBack in the main thread.\n");
    +
    + /*
    + * We could try to confirm that extended state is still preserved
    + * when we schedule. For now, the only indication of failure is
    + * a warning in the kernel logs.
    + */
    +
    + return 0;
    +}
    \
     
     \ /
      Last update: 2021-06-02 17:59    [W:3.768 / U:0.064 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site