[PATCH] UML - Fix signal frame alignment

[PATCH] UML - Fix signal frame alignment

[Jeff Dike]

This is both 2.6.20 and -stable material.

Use the same signal frame alignment calculations as the underlying
architecture.  x86_64 appeared to do this, but the "- 8" was really
subtracting 8 * sizeof(struct rt_sigframe) rather than 8 bytes.

UML/i386 might have been OK, but I changed the calculation to match
i386 just to be sure.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
--
 arch/um/sys-i386/signal.c   |    3 ++-
 arch/um/sys-x86_64/signal.c |    5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

Index: linux-2.6.18-mm/arch/um/sys-x86_64/signal.c
===================================================================
--- linux-2.6.18-mm.orig/arch/um/sys-x86_64/signal.c	2007-01-29 14:20:57.000000000 -0500
+++ linux-2.6.18-mm/arch/um/sys-x86_64/signal.c	2007-01-30 11:46:38.000000000 -0500
@@ -191,8 +191,9 @@ int setup_signal_stack_si(unsigned long 
 	struct task_struct *me = current;
 
 	frame = (struct rt_sigframe __user *)
-		round_down(stack_top - sizeof(struct rt_sigframe), 16) - 8;
-        frame = (struct rt_sigframe __user *) ((unsigned long) frame - 128);
+		round_down(stack_top - sizeof(struct rt_sigframe), 16);
+	/* Subtract 128 for a red zone and 8 for proper alignment */
+        frame = (struct rt_sigframe __user *) ((unsigned long) frame - 128 - 8);
 
 	if (!access_ok(VERIFY_WRITE, fp, sizeof(struct _fpstate)))
 		goto out;
Index: linux-2.6.18-mm/arch/um/sys-i386/signal.c
===================================================================
--- linux-2.6.18-mm.orig/arch/um/sys-i386/signal.c	2007-01-17 06:02:52.000000000 -0500
+++ linux-2.6.18-mm/arch/um/sys-i386/signal.c	2007-01-30 11:39:10.000000000 -0500
@@ -219,7 +219,8 @@ int setup_signal_stack_sc(unsigned long 
 	unsigned long save_sp = PT_REGS_SP(regs);
 	int err = 0;
 
-	stack_top &= -8UL;
+	/* This is the same calculation as i386 - ((sp + 4) & 15) == 0 */
+	stack_top = ((stack_top + 4) & -16UL) - 4;
 	frame = (struct sigframe __user *) stack_top - 1;
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 		return 1;