[POWERPC] Make alignment exception always check exception table

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@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 10 insertions, 8 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 5ed4c2ceb5ca..c66b4771ef44 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -843,7 +843,7 @@ void __kprobes program_check_exception(struct pt_regs *regs)
 
 void alignment_exception(struct pt_regs *regs)
 {
-        int fixed = 0;
+        int sig, code, fixed = 0;
 
         /* we don't implement logging of alignment exceptions */
         if (!(current->thread.align_ctl & PR_UNALIGN_SIGBUS))
@@ -857,14 +857,16 @@ void alignment_exception(struct pt_regs *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;
+                sig = SIGSEGV;
+                code = SEGV_ACCERR;
+        } else {
+                sig = SIGBUS;
+                code = BUS_ADRALN;
         }
-        _exception(SIGBUS, regs, BUS_ADRALN, regs->dar);
+        if (user_mode(regs))
+                _exception(sig, regs, code, regs->dar);
+        else
+                bad_page_fault(regs, regs->dar, sig);
 }
 
 void StackOverflow(struct pt_regs *regs)