Patch "s390: fix normalization bug in exception table sorting" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

s390: fix normalization bug in exception table sorting

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
s390-fix-normalization-bug-in-exception-table-sorting.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ard Biesheuvel <[email protected]>
Date: Fri, 1 Jan 2016 13:39:22 +0100
Subject: s390: fix normalization bug in exception table sorting

From: Ard Biesheuvel <[email protected]>

commit bcb7825a77f41c7dd91da6f7ac10b928156a322e upstream.

The normalization pass in the sorting routine of the relative exception table serves two purposes:
- it ensures that the address fields of the exception table entries are fully ordered, so that no ambiguities arise between entries with identical instruction offsets (i.e., when two instructions that are exactly 8 bytes apart each have an exception table entry associated with them)
- it ensures that the offsets of both the instruction and the fixup fields of each entry are relative to their final location after sorting.

Commit eb608fb366de ("s390/exceptions: switch to relative exception table entries") ported the relative exception table format from x86, but modified the sorting routine to only normalize the instruction offset field and not the fixup offset field. The result is that the fixup offset of each entry will be relative to the original location of the entry before sorting, likely leading to crashes when those entries are dereferenced.

---
 arch/s390/mm/extable.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -52,12 +52,16 @@ void sort_extable(struct exception_table
 	int i;
 
 	/* Normalize entries to being relative to the start of the section */
-	for (p = start, i = 0; p < finish; p++, i += 8)
+	for (p = start, i = 0; p < finish; p++, i += 8) {
 		p->insn += i;
+		p->fixup += i + 4;
+	}
 	sort(start, finish - start, sizeof(*start), cmp_ex, NULL);
 	/* Denormalize all entries */
-	for (p = start, i = 0; p < finish; p++, i += 8)
+	for (p = start, i = 0; p < finish; p++, i += 8) {
 		p->insn -= i;
+		p->fixup -= i + 4;
+	}
 }
 
 #ifdef CONFIG_MODULES

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/s390-fix-normalization-bug-in-exception-table-sorting.patch