linux-kernel - [PATCH 4.9 109/119] arm64: hw_breakpoint: fix watchpoint matching for tagged pointers

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Date:   Mon, 12 Jun 2017 17:26:11 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: [PATCH 4.9 109/119] arm64: hw_breakpoint: fix watchpoint matching for tagged pointers

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit 7dcd9dd8cebe9fa626af7e2358d03a37041a70fb upstream.

This backport has a small difference from the upstream commit:
 - The address tag is removed in watchpoint_handler() instead of
   get_distance_from_watchpoint(), because 4.9 does not have commit
   fdfeff0f9e3d ("arm64: hw_breakpoint: Handle inexact watchpoint
   addresses").

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@....com>
Acked-by: Will Deacon <will.deacon@....com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/include/asm/uaccess.h  |    6 +++---
 arch/arm64/kernel/hw_breakpoint.c |    3 ++-
 2 files changed, 5 insertions(+), 4 deletions(-)

--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -105,9 +105,9 @@ 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)
 
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -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]);
@@ -696,7 +697,7 @@ 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. */