[PATCH] powerpc: Make alignment exception always check exception table

[Benjamin Herrenschmidt]

The alignment exception used to only check the exception table for
-EFAULT, not for other errors. That opens an oops window if we can
coerce the kernel into getting an alignment exception for other reasons
in what would normally be a user-protected accessor, which can be done
via some of the futex ops. This fixes it by always checking the
exception tables.

Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
---

This is 2.6.19 material and should probably go into stable as well.
(Greg: take it if paulus acks it and it applies :)

Index: linux-work/arch/powerpc/kernel/traps.c
===================================================================
--- linux-work.orig/arch/powerpc/kernel/traps.c	2006-10-23 14:41:37.000000000 +1000
+++ linux-work/arch/powerpc/kernel/traps.c	2006-10-30 13:59:41.000000000 +1100
@@ -843,7 +843,7 @@ void __kprobes program_check_exception(s
 
 void alignment_exception(struct pt_regs *regs)
 {
-	int fixed = 0;
+	int sig, fixed = 0;
 
 	/* we don't implement logging of alignment exceptions */
 	if (!(current->thread.align_ctl & PR_UNALIGN_SIGBUS))
@@ -856,15 +856,11 @@ void alignment_exception(struct pt_regs 
 	}
 
 	/* Operand address was bad */
-	if (fixed == -EFAULT) {
-		if (user_mode(regs))
-			_exception(SIGSEGV, regs, SEGV_ACCERR, regs->dar);
-		else
-			/* Search exception table */
-			bad_page_fault(regs, regs->dar, SIGSEGV);
-		return;
-	}
-	_exception(SIGBUS, regs, BUS_ADRALN, regs->dar);
+	sig = fixed == -EFAULT ? SIGSEGV : SIGBUS;
+	if (user_mode(regs))
+		_exception(sig, regs, SEGV_ACCERR, regs->dar);
+	else
+		bad_page_fault(regs, regs->dar, sig);
 }
 
 void StackOverflow(struct pt_regs *regs)