Patch "arm64: hw_breakpoint: fix watchpoint matching for tagged pointers" has been added to the 4.11-stable tree

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

arm64: hw_breakpoint: fix watchpoint matching for tagged pointers

to the 4.11-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:
arm64-hw_breakpoint-fix-watchpoint-matching-for-tagged-pointers.patch
and it can be found in the queue-4.11 subdirectory.

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

From: Kristina Martsenko <[email protected]>
Date: Wed, 3 May 2017 16:37:46 +0100
Subject: arm64: hw_breakpoint: fix watchpoint matching for tagged pointers

From: Kristina Martsenko <[email protected]>

commit 7dcd9dd8cebe9fa626af7e2358d03a37041a70fb upstream.

When we take a watchpoint exception, the address that triggered the watchpoint is found in FAR_EL1. We compare it to the address of each configured watchpoint to see which one was hit.

The configured watchpoint addresses are untagged, while the address in FAR_EL1 will have an address tag if the data access was done using a tagged address. The tag needs to be removed to compare the address to the watchpoints.

Currently we don't remove it, and as a result can report the wrong watchpoint as being hit (specifically, always either the highest TTBR0 watchpoint or lowest TTBR1 watchpoint). This patch removes the tag.

---
 arch/arm64/include/asm/uaccess.h  |    6 +++---
 arch/arm64/kernel/hw_breakpoint.c |    3 +++
 2 files changed, 6 insertions(+), 3 deletions(-)

@@ -107,9 +107,9 @@ static inline void set_fs(mm_segment_t f
 })
 
 /*
- * When dealing with data aborts or instruction traps we may end up with
- * a tagged userland pointer. Clear the tag to get a sane pointer to pass
- * on to access_ok(), for instance.
+ * When dealing with data aborts, watchpoints, or instruction traps we may end
+ * up with a tagged userland pointer. Clear the tag to get a sane pointer to
+ * pass on to access_ok(), for instance.
  */
 #define untagged_addr(addr)		sign_extend64(addr, 55)
 

@@ -36,6 +36,7 @@
 #include <asm/traps.h>
 #include <asm/cputype.h>
 #include <asm/system_misc.h>
+#include <asm/uaccess.h>
 
 /* Breakpoint currently in use for each BRP. */
 static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);

@@ -721,6 +722,8 @@ static u64 get_distance_from_watchpoint(
 	u64 wp_low, wp_high;
 	u32 lens, lene;
 
+	addr = untagged_addr(addr);
+
 	lens = __ffs(ctrl->len);
 	lene = __fls(ctrl->len);
 

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

queue-4.11/arm64-hw_breakpoint-fix-watchpoint-matching-for-tagged-pointers.patch queue-4.11/arm64-entry-improve-data-abort-handling-of-tagged-pointers.patch queue-4.11/arm64-documentation-document-tagged-pointer-stack-constraints.patch queue-4.11/arm64-traps-fix-userspace-cache-maintenance-emulation-on-a-tagged-pointer.patch