From eca91e7838ec92e8c12122849ec7539c4765b689 Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Thu, 10 Jul 2008 14:50:39 -0700 Subject: x86_64: fix delayed signals On three of the several paths in entry_64.S that call do_notify_resume() on the way back to user mode, we fail to properly check again for newly-arrived work that requires another call to do_notify_resume() before going to user mode. These paths set the mask to check only _TIF_NEED_RESCHED, but this is wrong. The other paths that lead to do_notify_resume() do this correctly already, and entry_32.S does it correctly in all cases. All paths back to user mode have to check all the _TIF_WORK_MASK flags at the last possible stage, with interrupts disabled. Otherwise, we miss any flags (TIF_SIGPENDING for example) that were set any time after we entered do_notify_resume(). More work flags can be set (or left set) synchronously inside do_notify_resume(), as TIF_SIGPENDING can be, or asynchronously by interrupts or other CPUs (which then send an asynchronous interrupt). There are many different scenarios that could hit this bug, most of them races. The simplest one to demonstrate does not require any race: when one signal has done handler setup at the check before returning from a syscall, and there is another signal pending that should be handled. The second signal's handler should interrupt the first signal handler before it actually starts (so the interrupted PC is still at the handler's entry point). Instead, it runs away until the next kernel entry (next syscall, tick, etc). This test behaves correctly on 32-bit kernels, and fails on 64-bit (either 32-bit or 64-bit test binary). With this fix, it works. #define _GNU_SOURCE #include #include #include #include #ifndef REG_RIP #define REG_RIP REG_EIP #endif static sig_atomic_t hit1, hit2; static void handler (int sig, siginfo_t *info, void *ctx) { ucontext_t *uc = ctx; if ((void *) uc->uc_mcontext.gregs[REG_RIP] == &handler) { if (sig == SIGUSR1) hit1 = 1; else hit2 = 1; } printf ("%s at %#lx\n", strsignal (sig), uc->uc_mcontext.gregs[REG_RIP]); } int main (void) { struct sigaction sa; sigset_t set; sigemptyset (&sa.sa_mask); sa.sa_flags = SA_SIGINFO; sa.sa_sigaction = &handler; if (sigaction (SIGUSR1, &sa, NULL) || sigaction (SIGUSR2, &sa, NULL)) return 2; sigemptyset (&set); sigaddset (&set, SIGUSR1); sigaddset (&set, SIGUSR2); if (sigprocmask (SIG_BLOCK, &set, NULL)) return 3; printf ("main at %p, handler at %p\n", &main, &handler); raise (SIGUSR1); raise (SIGUSR2); if (sigprocmask (SIG_UNBLOCK, &set, NULL)) return 4; if (hit1 + hit2 == 1) { puts ("PASS"); return 0; } puts ("FAIL"); return 1; } Signed-off-by: Roland McGrath Cc: Andrew Morton Cc: Linus Torvalds Signed-off-by: Ingo Molnar --- arch/x86/kernel/entry_64.S | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) (limited to 'arch') diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 466b928..bb4e22f 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -306,7 +306,7 @@ sysret_signal: leaq -ARGOFFSET(%rsp),%rdi # &pt_regs -> arg1 xorl %esi,%esi # oldset -> arg2 call ptregscall_common -1: movl $_TIF_NEED_RESCHED,%edi +1: movl $_TIF_WORK_MASK,%edi /* Use IRET because user could have changed frame. This works because ptregscall_common has called FIXUP_TOP_OF_STACK. */ DISABLE_INTERRUPTS(CLBR_NONE) @@ -394,7 +394,7 @@ int_signal: movq %rsp,%rdi # &ptregs -> arg1 xorl %esi,%esi # oldset -> arg2 call do_notify_resume -1: movl $_TIF_NEED_RESCHED,%edi +1: movl $_TIF_WORK_MASK,%edi int_restore_rest: RESTORE_REST DISABLE_INTERRUPTS(CLBR_NONE) @@ -647,9 +647,8 @@ retint_signal: RESTORE_REST DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF - movl $_TIF_NEED_RESCHED,%edi GET_THREAD_INFO(%rcx) - jmp retint_check + jmp retint_with_reschedule #ifdef CONFIG_PREEMPT /* Returning to kernel space. Check if we need preemption */ -- cgit v1.1