sigaltstack needs to be disabled before the signal handler can
safely use swapcontext().
This patch adds the SS_AUTODISARM flag.
This flag disables the sigaltstack when entering the signal handler.
When returning from signal handler, the sigaltstack is restored by
uc_stack.
CC: Shuah Khan <shua...@osg.samsung.com>
CC: linux-kernel@vger.kernel.org
CC: linux-...@vger.kernel.org
CC: Andy Lutomirski <l...@amacapital.net>
Signed-off-by: Stas Sergeev <s...@users.sourceforge.net>
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/sigaltstack/Makefile | 8 ++
tools/testing/selftests/sigaltstack/sas.c | 156 +++++++++++++++++++++++++++
3 files changed, 165 insertions(+)
create mode 100644 tools/testing/selftests/sigaltstack/Makefile
create mode 100644 tools/testing/selftests/sigaltstack/sas.c
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index b04afc3..ff9e5f2 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -19,6 +19,7 @@ TARGETS += powerpc
TARGETS += pstore
TARGETS += ptrace
TARGETS += seccomp
+TARGETS += sigaltstack
TARGETS += size
TARGETS += static_keys
TARGETS += sysctl
diff --git a/tools/testing/selftests/sigaltstack/Makefile
b/tools/testing/selftests/sigaltstack/Makefile
new file mode 100644
index 0000000..56af56e
--- /dev/null
+++ b/tools/testing/selftests/sigaltstack/Makefile
@@ -0,0 +1,8 @@
+CFLAGS = -Wall
+BINARIES = sas
+all: $(BINARIES)
+
+include ../lib.mk
+
+clean:
+ rm -rf $(BINARIES)
diff --git a/tools/testing/selftests/sigaltstack/sas.c
b/tools/testing/selftests/sigaltstack/sas.c
new file mode 100644
index 0000000..57da8bf
--- /dev/null
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -0,0 +1,156 @@
+/*
+ * Stas Sergeev <s...@users.sourceforge.net>
+ *
+ * test sigaltstack(SS_ONSTACK | SS_AUTODISARM)
+ * If that succeeds, then swapcontext() can be used inside sighandler safely.
+ *
+ */
+
+#define _GNU_SOURCE
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <ucontext.h>
+#include <alloca.h>
+#include <string.h>
+#include <assert.h>
+
+#ifndef SS_AUTODISARM
+#define SS_AUTODISARM (1 << 4)
+#endif
+
+static void *sstack, *ustack;
+static ucontext_t uc, sc;
+static const char *msg = "[OK]\tStack preserved";
+static const char *msg2 = "[FAIL]\tStack corrupted";
+struct stk_data {
+ char msg[128];
+ int flag;
+};
+
+void my_usr1(int sig, siginfo_t *si, void *u)
+{
+ char *aa;
+ int err;
+ stack_t stk;
+ struct stk_data *p;
+
+ register unsigned long sp asm("sp");
+
+ if (sp < (unsigned long)sstack ||
+ sp >= (unsigned long)sstack + SIGSTKSZ) {
+ printf("[FAIL]\tSP is not on sigaltstack\n");
+ exit(EXIT_FAILURE);
+ }
+ /* put some data on stack. other sighandler will try to overwrite it */
+ aa = alloca(1024);
+ assert(aa);
+ p = (struct stk_data *)(aa + 512);
+ strcpy(p->msg, msg);
+ p->flag = 1;
+ printf("[RUN]\tsignal USR1\n");
+ err = sigaltstack(NULL, &stk);
+ if (err) {
+ perror("[FAIL]\tsigaltstack()");
+ exit(EXIT_FAILURE);
+ }
+ if (stk.ss_flags != SS_DISABLE)
+ printf("[FAIL]\tss_flags=%i, should be SS_DISABLE\n",
+ stk.ss_flags);
+ else
+ printf("[OK]\tsigaltstack is disabled in sighandler\n");
+ swapcontext(&sc, &uc);
+ printf("%s\n", p->msg);
+ if (!p->flag) {
+ printf("[RUN]\tAborting\n");
+ exit(EXIT_FAILURE);
+ }
+}
+
+void my_usr2(int sig, siginfo_t *si, void *u)
+{
+ char *aa;
+ struct stk_data *p;
+
+ printf("[RUN]\tsignal USR2\n");
+ aa = alloca(1024);
+ /* dont run valgrind on this */
+ /* try to find the data stored by previous sighandler */
+ p = memmem(aa, 1024, msg, strlen(msg));
+ if (p) {
+ printf("[FAIL]\tsigaltstack re-used\n");
+ /* corrupt the data */
+ strcpy(p->msg, msg2);
+ /* tell other sighandler that his data is corrupted */
+ p->flag = 0;
+ }
+}
+
+static void switch_fn(void)
+{
+ printf("[RUN]\tswitched to user ctx\n");
+ raise(SIGUSR2);
+ setcontext(&sc);
+}
+
+int main(void)
+{
+ struct sigaction act;
+ stack_t stk;
+ int err;
+
+ sigemptyset(&act.sa_mask);
+ act.sa_flags = SA_ONSTACK | SA_SIGINFO;
+ act.sa_sigaction = my_usr1;
+ sigaction(SIGUSR1, &act, NULL);
+ act.sa_sigaction = my_usr2;
+ sigaction(SIGUSR2, &act, NULL);
+ sstack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+ if (sstack == MAP_FAILED) {
+ perror("mmap()");
+ return EXIT_FAILURE;
+ }
+ stk.ss_sp = sstack;
+ stk.ss_size = SIGSTKSZ;
+ stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
+ err = sigaltstack(&stk, NULL);
+ if (err) {
+ perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
+ stk.ss_flags = SS_ONSTACK;
+ }
+ err = sigaltstack(&stk, NULL);
+ if (err) {
+ perror("[FAIL]\tsigaltstack(SS_ONSTACK)");
+ return EXIT_FAILURE;
+ }
+
+ ustack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+ if (ustack == MAP_FAILED) {
+ perror("mmap()");
+ return EXIT_FAILURE;
+ }
+ getcontext(&uc);
+ uc.uc_link = NULL;
+ uc.uc_stack.ss_sp = ustack;
+ uc.uc_stack.ss_size = SIGSTKSZ;
+ makecontext(&uc, switch_fn, 0);
+ raise(SIGUSR1);
+
+ err = sigaltstack(NULL, &stk);
+ if (err) {
+ perror("[FAIL]\tsigaltstack()");
+ exit(EXIT_FAILURE);
+ }
+ if (stk.ss_flags != 0) {
+ printf("[FAIL]\tss_flags=%i, should be 0\n",
+ stk.ss_flags);
+ exit(EXIT_FAILURE);
+ }
+ printf("[OK]\tsigaltstack is enabled after signal\n");
+
+ printf("[OK]\tTest passed\n");
+ return 0;
+}
--
2.7.2
