selftests/sigaltstack: Add new testcase for sigaltstack(SS_ONSTACK|SS_AUTODISARM)

This patch adds the test case for SS_AUTODISARM flag.
The test-case tries to set SS_AUTODISARM flag and checks if
the nested signal corrupts the stack after swapcontext().

Signed-off-by: Stas Sergeev <stsp@list.ru>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-api@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1460665206-13646-5-git-send-email-stsp@list.ru
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 165 insertions, 0 deletions

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index b04afc3295df..ff9e5f20a5a7 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 000000000000..56af56eda6fa
--- /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 000000000000..57da8bfde60b
--- /dev/null
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -0,0 +1,156 @@
+/*
+ * Stas Sergeev <stsp@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;
+}