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authorAl Viro <viro@zeniv.linux.org.uk>2010-09-17 09:34:39 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2010-09-17 13:22:18 -0400
commit653d48b22166db2d8b1515ebe6f9f0f7c95dfc86 (patch)
treeed6f5dbb1a3133588a0db7b534bfbff76c05e552 /arch/arm/kernel/entry-common.S
parenta5b617368c8d61072844ac267aaf140e489b808b (diff)
arm: fix really nasty sigreturn bug
If a signal hits us outside of a syscall and another gets delivered when we are in sigreturn (e.g. because it had been in sa_mask for the first one and got sent to us while we'd been in the first handler), we have a chance of returning from the second handler to location one insn prior to where we ought to return. If r0 happens to contain -513 (-ERESTARTNOINTR), sigreturn will get confused into doing restart syscall song and dance. Incredible joy to debug, since it manifests as random, infrequent and very hard to reproduce double execution of instructions in userland code... The fix is simple - mark it "don't bother with restarts" in wrapper, i.e. set r8 to 0 in sys_sigreturn and sys_rt_sigreturn wrappers, suppressing the syscall restart handling on return from these guys. They can't legitimately return a restart-worthy error anyway. Testcase: #include <unistd.h> #include <signal.h> #include <stdlib.h> #include <sys/time.h> #include <errno.h> void f(int n) { __asm__ __volatile__( "ldr r0, [%0]\n" "b 1f\n" "b 2f\n" "1:b .\n" "2:\n" : : "r"(&n)); } void handler1(int sig) { } void handler2(int sig) { raise(1); } void handler3(int sig) { exit(0); } main() { struct sigaction s = {.sa_handler = handler2}; struct itimerval t1 = { .it_value = {1} }; struct itimerval t2 = { .it_value = {2} }; signal(1, handler1); sigemptyset(&s.sa_mask); sigaddset(&s.sa_mask, 1); sigaction(SIGALRM, &s, NULL); signal(SIGVTALRM, handler3); setitimer(ITIMER_REAL, &t1, NULL); setitimer(ITIMER_VIRTUAL, &t2, NULL); f(-513); /* -ERESTARTNOINTR */ write(1, "buggered\n", 9); return 1; } Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/arm/kernel/entry-common.S')
-rw-r--r--arch/arm/kernel/entry-common.S2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index f05a35a59694..1b560825e1cf 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -418,11 +418,13 @@ ENDPROC(sys_clone_wrapper)
418 418
419sys_sigreturn_wrapper: 419sys_sigreturn_wrapper:
420 add r0, sp, #S_OFF 420 add r0, sp, #S_OFF
421 mov why, #0 @ prevent syscall restart handling
421 b sys_sigreturn 422 b sys_sigreturn
422ENDPROC(sys_sigreturn_wrapper) 423ENDPROC(sys_sigreturn_wrapper)
423 424
424sys_rt_sigreturn_wrapper: 425sys_rt_sigreturn_wrapper:
425 add r0, sp, #S_OFF 426 add r0, sp, #S_OFF
427 mov why, #0 @ prevent syscall restart handling
426 b sys_rt_sigreturn 428 b sys_rt_sigreturn
427ENDPROC(sys_rt_sigreturn_wrapper) 429ENDPROC(sys_rt_sigreturn_wrapper)
428 430