linux-kernel - [PATCH 3.16 126/134] arm64: uaccess: ensure extension of access

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Message-ID: <lsq.1503062000.319149062@decadent.org.uk>
Date:   Fri, 18 Aug 2017 14:13:20 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Will Deacon" <will.deacon@....com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Mark Rutland" <mark.rutland@....com>
Subject: [PATCH 3.16 126/134] arm64: uaccess: ensure extension of
 access_ok() addr

3.16.47-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Mark Rutland <mark.rutland@....com>

commit a06040d7a791a9177581dcf7293941bd92400856 upstream.

Our access_ok() simply hands its arguments over to __range_ok(), which
implicitly assummes that the addr parameter is 64 bits wide. This isn't
necessarily true for compat code, which might pass down a 32-bit address
parameter.

In these cases, we don't have a guarantee that the address has been zero
extended to 64 bits, and the upper bits of the register may contain
unknown values, potentially resulting in a suprious failure.

Avoid this by explicitly casting the addr parameter to an unsigned long
(as is done on other architectures), ensuring that the parameter is
widened appropriately.

Fixes: 0aea86a2176c ("arm64: User access library functions")
Acked-by: Will Deacon <will.deacon@....com>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm64/include/asm/uaccess.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -89,11 +89,12 @@ static inline void set_fs(mm_segment_t f
  */
 #define __range_ok(addr, size)						\
 ({									\
+	unsigned long __addr = (unsigned long __force)(addr);		\
 	unsigned long flag, roksum;					\
 	__chk_user_ptr(addr);						\
 	asm("adds %1, %1, %3; ccmp %1, %4, #2, cc; cset %0, ls"		\
 		: "=&r" (flag), "=&r" (roksum)				\
-		: "1" (addr), "Ir" (size),				\
+		: "1" (__addr), "Ir" (size),				\
 		  "r" (current_thread_info()->addr_limit)		\
 		: "cc");						\
 	flag;								\