signals/sigaltstack: Report current flag bits in sigaltstack()

sigaltstack()'s reported previous state uses a somewhat odd
convention, but the concept of flag bits is new, and we can do the
flag bits sensibly.  Specifically, let's just report them directly.

This will allow saving and restoring the sigaltstack state using
sigaltstack() to work correctly.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Amanieu d'Antras <amanieu@gmail.com>
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: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Stas Sergeev <stsp@list.ru>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: linux-api@vger.kernel.org
Link: http://lkml.kernel.org/r/94b291ec9fd47741a9264851e316e158ded0b00d.1462296606.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index bf97ea5775ae30959fde4ada06391ad2ee015fec..ab122a2cee417e806d002fb8eed27756b1e89dcf 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3099,7 +3099,8 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s
 
        oss.ss_sp = (void __user *) current->sas_ss_sp;
        oss.ss_size = current->sas_ss_size;
-       oss.ss_flags = sas_ss_flags(sp);
+       oss.ss_flags = sas_ss_flags(sp) |
+               (current->sas_ss_flags & SS_FLAG_BITS);
 
        if (uss) {
                void __user *ss_sp;

diff --git a/tools/testing/selftests/sigaltstack/sas.c b/tools/testing/selftests/sigaltstack/sas.c
index a98c3ef8141f1666aa1ea2842b0853dd1a21efff..4280d0699792cfaf5d5a378bf166553e68bd594f 100644 (file)
--- a/tools/testing/selftests/sigaltstack/sas.c
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -113,6 +113,19 @@ int main(void)
                perror("mmap()");
                return EXIT_FAILURE;
        }
+
+       err = sigaltstack(NULL, &stk);
+       if (err) {
+               perror("[FAIL]\tsigaltstack()");
+               exit(EXIT_FAILURE);
+       }
+       if (stk.ss_flags == SS_DISABLE) {
+               printf("[OK]\tInitial sigaltstack state was SS_DISABLE\n");
+       } else {
+               printf("[FAIL]\tInitial sigaltstack state was %i; should have been SS_DISABLE\n", stk.ss_flags);
+               return EXIT_FAILURE;
+       }
+
        stk.ss_sp = sstack;
        stk.ss_size = SIGSTKSZ;
        stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
@@ -151,12 +164,12 @@ int main(void)
                perror("[FAIL]\tsigaltstack()");
                exit(EXIT_FAILURE);
        }
-       if (stk.ss_flags != 0) {
-               printf("[FAIL]\tss_flags=%i, should be 0\n",
+       if (stk.ss_flags != SS_AUTODISARM) {
+               printf("[FAIL]\tss_flags=%i, should be SS_AUTODISARM\n",
                                stk.ss_flags);
                exit(EXIT_FAILURE);
        }
-       printf("[OK]\tsigaltstack is enabled after signal\n");
+       printf("[OK]\tsigaltstack is still SS_AUTODISARM after signal\n");
 
        printf("[OK]\tTest passed\n");
        return 0;