[PATCH] x86_64: never block forced SIGSEGV

This is the x86_64 version of the signal fix I just posted for i386.

This problem was first noticed on PPC and has already been fixed there.
But the exact same issue applies to other platforms in the same way.  The
signal blocking for sa_mask and the handled signal takes place after the
handler setup.  When the stack is bogus, the handler setup forces a
SIGSEGV.  But then this will be blocked, and returning to user mode will
fault again and iterate.  This patch fixes the problem by checking whether
signal handler setup failed, and not doing the signal-blocking if so.  This
copies what was done in the ppc code.  I think all architectures' signal
handler setup code follows this pattern and needs the change.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/ia32/ia32_signal.c

@@ -428,8 +428,8 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
 	return (void __user *)((rsp - frame_size) & -8UL);
 }
 
-void ia32_setup_frame(int sig, struct k_sigaction *ka,
-			compat_sigset_t *set, struct pt_regs * regs)
+int ia32_setup_frame(int sig, struct k_sigaction *ka,
+		     compat_sigset_t *set, struct pt_regs * regs)
 {
 	struct sigframe __user *frame;
 	int err = 0;
@@ -514,14 +514,15 @@ void ia32_setup_frame(int sig, struct k_sigaction *ka,
 		current->comm, current->pid, frame, regs->rip, frame->pretcode);
 #endif
 
-	return;
+	return 1;
 
 give_sigsegv:
 	force_sigsegv(sig, current);
+	return 0;
 }
 
-void ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
-			   compat_sigset_t *set, struct pt_regs * regs)
+int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
+			compat_sigset_t *set, struct pt_regs * regs)
 {
 	struct rt_sigframe __user *frame;
 	int err = 0;
@@ -613,9 +614,9 @@ void ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 		current->comm, current->pid, frame, regs->rip, frame->pretcode);
 #endif
 
-	return;
+	return 1;
 
 give_sigsegv:
 	force_sigsegv(sig, current);
+	return 0;
 }
-

arch/x86_64/kernel/signal.c

@@ -34,9 +34,9 @@
 
 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
 
-void ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
+int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                sigset_t *set, struct pt_regs * regs); 
-void ia32_setup_frame(int sig, struct k_sigaction *ka,
+int ia32_setup_frame(int sig, struct k_sigaction *ka,
             sigset_t *set, struct pt_regs * regs); 
 
 asmlinkage long
@@ -238,7 +238,7 @@ get_stack(struct k_sigaction *ka, struct pt_regs *regs, unsigned long size)
 	return (void __user *)round_down(rsp - size, 16); 
 }
 
-static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
+static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 			   sigset_t *set, struct pt_regs * regs)
 {
 	struct rt_sigframe __user *frame;
@@ -327,20 +327,23 @@ static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 		current->comm, current->pid, frame, regs->rip, frame->pretcode);
 #endif
 
-	return;
+	return 1;
 
 give_sigsegv:
 	force_sigsegv(sig, current);
+	return 0;
 }
 
 /*
  * OK, we're invoking a handler
  */	
 
-static void
+static int
 handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 		sigset_t *oldset, struct pt_regs *regs)
 {
+	int ret;
+
 #ifdef DEBUG_SIG
 	printk("handle_signal pid:%d sig:%lu rip:%lx rsp:%lx regs=%p\n",
 		current->pid, sig,
@@ -384,20 +387,22 @@ handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 #ifdef CONFIG_IA32_EMULATION
 	if (test_thread_flag(TIF_IA32)) {
 		if (ka->sa.sa_flags & SA_SIGINFO)
-			ia32_setup_rt_frame(sig, ka, info, oldset, regs);
+			ret = ia32_setup_rt_frame(sig, ka, info, oldset, regs);
 		else
-			ia32_setup_frame(sig, ka, oldset, regs);
+			ret = ia32_setup_frame(sig, ka, oldset, regs);
 	} else 
 #endif
-	setup_rt_frame(sig, ka, info, oldset, regs);
+	ret = setup_rt_frame(sig, ka, info, oldset, regs);
 
-	if (!(ka->sa.sa_flags & SA_NODEFER)) {
+	if (ret && !(ka->sa.sa_flags & SA_NODEFER)) {
 		spin_lock_irq(&current->sighand->siglock);
 		sigorsets(&current->blocked,&current->blocked,&ka->sa.sa_mask);
 		sigaddset(&current->blocked,sig);
 		recalc_sigpending();
 		spin_unlock_irq(&current->sighand->siglock);
 	}
+
+	return ret;
 }
 
 /*
@@ -437,8 +442,7 @@ int do_signal(struct pt_regs *regs, sigset_t *oldset)
 			asm volatile("movq %0,%%db7"	: : "r" (current->thread.debugreg7));
 
 		/* Whee!  Actually deliver the signal.  */
-		handle_signal(signr, &info, &ka, oldset, regs);
-		return 1;
+		return handle_signal(signr, &info, &ka, oldset, regs);
 	}
 
  no_signal: