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+/*
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+ * Stas Sergeev <stsp@users.sourceforge.net>
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+ *
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+ * test sigaltstack(SS_ONSTACK | SS_AUTODISARM)
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+ * If that succeeds, then swapcontext() can be used inside sighandler safely.
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+ *
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+ */
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+
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+#define _GNU_SOURCE
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+#include <signal.h>
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+#include <stdio.h>
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+#include <stdlib.h>
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+#include <sys/mman.h>
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+#include <ucontext.h>
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+#include <alloca.h>
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+#include <string.h>
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+#include <assert.h>
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+#include <errno.h>
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+
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+#ifndef SS_AUTODISARM
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+#define SS_AUTODISARM (1U << 31)
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+#endif
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+
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+static void *sstack, *ustack;
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+static ucontext_t uc, sc;
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+static const char *msg = "[OK]\tStack preserved";
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+static const char *msg2 = "[FAIL]\tStack corrupted";
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+struct stk_data {
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+ char msg[128];
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+ int flag;
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+};
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+
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+void my_usr1(int sig, siginfo_t *si, void *u)
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+{
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+ char *aa;
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+ int err;
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+ stack_t stk;
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+ struct stk_data *p;
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+
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+ register unsigned long sp asm("sp");
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+
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+ if (sp < (unsigned long)sstack ||
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+ sp >= (unsigned long)sstack + SIGSTKSZ) {
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+ printf("[FAIL]\tSP is not on sigaltstack\n");
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+ exit(EXIT_FAILURE);
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+ }
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+ /* put some data on stack. other sighandler will try to overwrite it */
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+ aa = alloca(1024);
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+ assert(aa);
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+ p = (struct stk_data *)(aa + 512);
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+ strcpy(p->msg, msg);
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+ p->flag = 1;
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+ printf("[RUN]\tsignal USR1\n");
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+ err = sigaltstack(NULL, &stk);
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+ if (err) {
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+ perror("[FAIL]\tsigaltstack()");
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+ exit(EXIT_FAILURE);
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+ }
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+ if (stk.ss_flags != SS_DISABLE)
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+ printf("[FAIL]\tss_flags=%i, should be SS_DISABLE\n",
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+ stk.ss_flags);
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+ else
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+ printf("[OK]\tsigaltstack is disabled in sighandler\n");
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+ swapcontext(&sc, &uc);
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+ printf("%s\n", p->msg);
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+ if (!p->flag) {
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+ printf("[RUN]\tAborting\n");
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+ exit(EXIT_FAILURE);
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+ }
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+}
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+
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+void my_usr2(int sig, siginfo_t *si, void *u)
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+{
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+ char *aa;
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+ struct stk_data *p;
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+
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+ printf("[RUN]\tsignal USR2\n");
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+ aa = alloca(1024);
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+ /* dont run valgrind on this */
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+ /* try to find the data stored by previous sighandler */
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+ p = memmem(aa, 1024, msg, strlen(msg));
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+ if (p) {
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+ printf("[FAIL]\tsigaltstack re-used\n");
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+ /* corrupt the data */
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+ strcpy(p->msg, msg2);
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+ /* tell other sighandler that his data is corrupted */
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+ p->flag = 0;
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+ }
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+}
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+
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+static void switch_fn(void)
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+{
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+ printf("[RUN]\tswitched to user ctx\n");
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+ raise(SIGUSR2);
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+ setcontext(&sc);
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+}
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+
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+int main(void)
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+{
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+ struct sigaction act;
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+ stack_t stk;
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+ int err;
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+
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+ sigemptyset(&act.sa_mask);
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+ act.sa_flags = SA_ONSTACK | SA_SIGINFO;
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+ act.sa_sigaction = my_usr1;
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+ sigaction(SIGUSR1, &act, NULL);
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+ act.sa_sigaction = my_usr2;
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+ sigaction(SIGUSR2, &act, NULL);
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+ sstack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
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+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
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+ if (sstack == MAP_FAILED) {
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+ perror("mmap()");
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+ return EXIT_FAILURE;
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+ }
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+
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+ err = sigaltstack(NULL, &stk);
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+ if (err) {
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+ perror("[FAIL]\tsigaltstack()");
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+ exit(EXIT_FAILURE);
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+ }
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+ if (stk.ss_flags == SS_DISABLE) {
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+ printf("[OK]\tInitial sigaltstack state was SS_DISABLE\n");
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+ } else {
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+ printf("[FAIL]\tInitial sigaltstack state was %i; should have been SS_DISABLE\n", stk.ss_flags);
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+ return EXIT_FAILURE;
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+ }
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+
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+ stk.ss_sp = sstack;
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+ stk.ss_size = SIGSTKSZ;
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+ stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
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+ err = sigaltstack(&stk, NULL);
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+ if (err) {
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+ if (errno == EINVAL) {
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+ printf("[NOTE]\tThe running kernel doesn't support SS_AUTODISARM\n");
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+ /*
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+ * If test cases for the !SS_AUTODISARM variant were
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+ * added, we could still run them. We don't have any
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+ * test cases like that yet, so just exit and report
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+ * success.
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+ */
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+ return 0;
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+ } else {
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+ perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
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+ return EXIT_FAILURE;
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+ }
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+ }
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+
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+ ustack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
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+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
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+ if (ustack == MAP_FAILED) {
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+ perror("mmap()");
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+ return EXIT_FAILURE;
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+ }
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+ getcontext(&uc);
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+ uc.uc_link = NULL;
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+ uc.uc_stack.ss_sp = ustack;
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+ uc.uc_stack.ss_size = SIGSTKSZ;
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+ makecontext(&uc, switch_fn, 0);
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+ raise(SIGUSR1);
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+
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+ err = sigaltstack(NULL, &stk);
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+ if (err) {
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+ perror("[FAIL]\tsigaltstack()");
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+ exit(EXIT_FAILURE);
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+ }
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+ if (stk.ss_flags != SS_AUTODISARM) {
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+ printf("[FAIL]\tss_flags=%i, should be SS_AUTODISARM\n",
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+ stk.ss_flags);
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+ exit(EXIT_FAILURE);
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+ }
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+ printf("[OK]\tsigaltstack is still SS_AUTODISARM after signal\n");
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+
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+ printf("[OK]\tTest passed\n");
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+ return 0;
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+}
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Linus Torvalds