// 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>

#include "kselftest.h" /* For __cpuid_count() */
#include "helpers.h"

static inline int xsave_enabled(void)
{
        unsigned int eax, ebx, ecx, edx;

        __cpuid_count(0x1, 0x0, eax, ebx, ecx, edx);

        /* Is CR4.OSXSAVE enabled ? */
        return ecx & (1U << 27);
}

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("\tWreck XSTATE header\n");
        /* Wreck the first reserved bytes in the header */
        *(xfeatures + 2) = 0xfffffff;
}

static void sigsegv(int sig, siginfo_t *info, void *uc_void)
{
        printf("\tGot SIGSEGV\n");
}

int main(void)
{
        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;
}