[patch 3/6] kprobes: Align probe address.

[Heiko Carstens]

From: David Wilder <dwilder@xxxxxxxxxx>

Running a probe on s390 with a probe address that is not 4 byte aligned
results in a Kernel BUG.  The problem is that the stura instruction used
by swap_instruction requires the destination address to be 4 byte aligned.
As stura only writes 4 bytes, aligning to the next 4 byte aligned address
results in the breakpoint instruction being stored past the probe address.
The fix is to align the address backward (to the previous 4 byte aligned
address) and writing the two byte breakpoint instruction in the appropriate
bytes.

Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: David Wilder <dwilder@xxxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
---

 arch/s390/kernel/kprobes.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/arch/s390/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/arch/s390/kernel/kprobes.c
+++ linux-2.6/arch/s390/kernel/kprobes.c
@@ -167,7 +167,7 @@ static int __kprobes swap_instruction(vo
 	 * shall not cross any page boundaries (vmalloc area!) when writing
 	 * the new instruction.
 	 */
-	addr = (u32 *)ALIGN((unsigned long)args->ptr, 4);
+	addr = (u32 *)((unsigned long)args->ptr & -4UL);
 	if ((unsigned long)args->ptr & 2)
 		instr = ((*addr) & 0xffff0000) | args->new;
 	else

-- 
-
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