Fix missing audit_syscall_exit() on ppc64 sigsuspend exit path

When we leave sigsuspend() directly into a signal handler, we don't want
to go via the normal syscall exit path -- it'll corrupt r4 and r5 which
are supposed to be giving information to the signal handler, and it'll
give us one more single-step SIGTRAP than we need if single-stepping is
in operation.

However, we _should_ be calling audit_syscall_exit(), which would
normally get invoked in that patch. It's not wonderfully pretty, but I
suspect the best answer is just to call it directly...
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

arch/ppc64/kernel/asm-offsets.c

@@ -68,6 +68,7 @@ int main(void)
 	DEFINE(THREAD_USED_VR, offsetof(struct thread_struct, used_vr));
 #endif /* CONFIG_ALTIVEC */
 	DEFINE(MM, offsetof(struct task_struct, mm));
+	DEFINE(AUDITCONTEXT, offsetof(struct task_struct, audit_context));
 
 	DEFINE(DCACHEL1LINESIZE, offsetof(struct ppc64_caches, dline_size));
 	DEFINE(DCACHEL1LOGLINESIZE, offsetof(struct ppc64_caches, log_dline_size));

arch/ppc64/kernel/entry.S

@@ -276,12 +276,20 @@ _GLOBAL(ppc64_rt_sigsuspend)
 _GLOBAL(ppc32_rt_sigsuspend)
 	bl	.save_nvgprs
 	bl	.sys32_rt_sigsuspend
-	/* If sigsuspend() returns zero, we are going into a signal handler */
 70:	cmpdi	0,r3,0
-	beq	.ret_from_except
-	/* If it returned -EINTR, we need to return via syscall_exit to set
+	/* If it returned an error, we need to return via syscall_exit to set
 	   the SO bit in cr0 and potentially stop for ptrace. */
-	b	syscall_exit
+	bne	syscall_exit
+	/* If sigsuspend() returns zero, we are going into a signal handler. We
+	   may need to call audit_syscall_exit() to mark the exit from sigsuspend() */
+	ld	r3,PACACURRENT(r13)
+	ld	r4,AUDITCONTEXT(r3)
+	cmpdi	0,r4,0
+	beq	.ret_from_except	/* No audit_context: Leave immediately. */
+	li	r4, 2			/* AUDITSC_FAILURE */
+	li	r5,-4			/* It's always -EINTR */
+	bl	.audit_syscall_exit
+	b	.ret_from_except
 
 _GLOBAL(ppc_fork)
 	bl	.save_nvgprs