Patch "arm64: hw_breakpoint: fix watchpoint matching for tagged pointers" has been added to the 4.4-stable tree

Patch "arm64: hw_breakpoint: fix watchpoint matching for tagged pointers" has been added to the 4.4-stable tree

[gregkh]

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 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 7dcd9dd8cebe9fa626af7e2358d03a37041a70fb Mon Sep 17 00:00:00 2001
From: Kristina Martsenko <kristina.martsenko@arm.com>
Date: Wed, 3 May 2017 16:37:46 +0100
Subject: arm64: hw_breakpoint: fix watchpoint matching for tagged pointers

From: Kristina Martsenko <kristina.martsenko@arm.com>

commit 7dcd9dd8cebe9fa626af7e2358d03a37041a70fb upstream.

This backport has a few small differences from the upstream commit:
 - The address tag is removed in watchpoint_handler() instead of
   get_distance_from_watchpoint(), because 4.4 does not have commit
   fdfeff0f9e3d ("arm64: hw_breakpoint: Handle inexact watchpoint
   addresses").
 - A macro is backported (untagged_addr), as it is not present in 4.4.

Original patch description:

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.

Fixes: d50240a5f6ce ("arm64: mm: permit use of tagged pointers at EL0")
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/include/asm/uaccess.h  |    8 ++++++++
 arch/arm64/kernel/hw_breakpoint.c |    3 ++-
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -21,6 +21,7 @@
 /*
  * User space memory access functions
  */
+#include <linux/bitops.h>
 #include <linux/string.h>
 #include <linux/thread_info.h>
 
@@ -103,6 +104,13 @@ static inline void set_fs(mm_segment_t f
 	flag;								\
 })
 
+/*
+ * 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)
+
 #define access_ok(type, addr, size)	__range_ok(addr, size)
 #define user_addr_max			get_fs
 
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -35,6 +35,7 @@
 #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]);
@@ -690,7 +691,7 @@ static int watchpoint_handler(unsigned l
 
 		/* Check if the watchpoint value matches. */
 		val = read_wb_reg(AARCH64_DBG_REG_WVR, i);
-		if (val != (addr & ~alignment_mask))
+		if (val != (untagged_addr(addr) & ~alignment_mask))
 			goto unlock;
 
 		/* Possible match, check the byte address select to confirm. */


Patches currently in stable-queue which might be from kristina.martsenko@arm.com are

queue-4.4/arm64-hw_breakpoint-fix-watchpoint-matching-for-tagged-pointers.patch
queue-4.4/arm64-entry-improve-data-abort-handling-of-tagged-pointers.patch