sigaltstack needs to be disabled before the signal handler can
safely use swapcontext(). Unfortunately linux implementation of
sigaltstack() returns EPERM in that case.
CC: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx
CC: linux-api@xxxxxxxxxxxxxxx
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Signed-off-by: Stas Sergeev <stsp@xxxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/sigaltstack/Makefile | 8 ++
tools/testing/selftests/sigaltstack/sas.c | 117
+++++++++++++++++++++++++++
3 files changed, 126 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 c8edff6..d5b2005 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -17,6 +17,7 @@ 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..1071718
--- /dev/null
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -0,0 +1,117 @@
+/*
+ * Stas Sergeev <stsp@xxxxxxxxxxxxxxxxxxxxx>
+ *
+ * test sigcontext(SS_DISABLE) inside signal handler
+ * If that succeeds, then swapcontext() can be used 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>
+
+static void *sstack, *ustack;
+static ucontext_t uc, sc;
+static const char *msg = "[OK]\tStack preserved";
+static const char *msg2 = "[FAIL]\tStack corrupted";
+
+void my_usr1(int sig)
+{
+ char *aa, *p;
+ int *i, err;
+ stack_t stk = { };
+
+ aa = alloca(1024);
+ assert(aa);
+ p = aa + 512;
+ strcpy(p, msg);
+ i = (int *) (p + 128);
+ *i = 1;
+ printf("[RUN]\tsignal USR1\n");
+ stk.ss_flags = SS_DISABLE;
+ err = sigaltstack(&stk, NULL);
+ if (err) {
+ perror("[FAIL]\tsigaltstack()");
+ /* don't exit to demonstrate the breakage */
+ /* exit(EXIT_FAILURE); */
+ }
+ swapcontext(&sc, &uc);
+ printf("%s\n", p);
+ if (!*i) {
+ printf("[RUN]\tAborting\n");
+ exit(EXIT_FAILURE);
+ }
+}
+
+void my_usr2(int sig)
+{
+ char *aa, *p;
+ int *i;
+
+ printf("[RUN]\tsignal USR2\n");
+ aa = alloca(1024);
+ /* dont run valgrind on this */
+ p = memmem(aa, 1024, msg, strlen(msg));
+ if (p) {
+ printf("[FAIL]\tsigaltstack re-used\n");
+ strcpy(p, msg2);
+ i = (int *) (p + 128);
+ *i = 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;
+ act.sa_handler = my_usr1;
+ sigaction(SIGUSR1, &act, NULL);
+ act.sa_handler = 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;
+ err = sigaltstack(&stk, NULL);
+ if (err) {
+ perror("sigaltstack()");
+ 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);
+ printf("[OK]\tTest passed\n");
+ return 0;
+}
--
2.4.3
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