From fd9beff0ccd0ef44078be23d6ce5ba431e23f292 Mon Sep 17 00:00:00 2001 From: Vincent Whitchurch Date: Fri, 9 Nov 2018 10:12:30 +0100 Subject: ARM: 8813/1: Make aligned 2-byte getuser()/putuser() atomic on ARMv6+ [ Upstream commit 344eb5539abf3e0b6ce22568c03e86450073e097 ] getuser() and putuser() (and there underscored variants) use two strb[t]/ldrb[t] instructions when they are asked to get/put 16-bits. This means that the read/write is not atomic even when performed to a 16-bit-aligned address. This leads to problems with vhost: vhost uses __getuser() to read the vring's 16-bit avail.index field, and if it happens to observe a partial update of the index, wrong descriptors will be used which will lead to a breakdown of the virtio communication. A similar problem exists for __putuser() which is used to write to the vring's used.index field. The reason these functions use strb[t]/ldrb[t] is because strht/ldrht instructions did not exist until ARMv6T2/ARMv7. So we should be easily able to fix this on ARMv7. Also, since all ARMv6 processors also don't actually use the unprivileged instructions anymore for uaccess (since CONFIG_CPU_USE_DOMAINS is not used) we can easily fix them too. Signed-off-by: Vincent Whitchurch Signed-off-by: Russell King Signed-off-by: Sasha Levin --- arch/arm/include/asm/uaccess.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'arch/arm/include') diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h index 0f6c6b873bc5..e05c31af48d1 100644 --- a/arch/arm/include/asm/uaccess.h +++ b/arch/arm/include/asm/uaccess.h @@ -379,6 +379,13 @@ do { \ #define __get_user_asm_byte(x, addr, err) \ __get_user_asm(x, addr, err, ldrb) +#if __LINUX_ARM_ARCH__ >= 6 + +#define __get_user_asm_half(x, addr, err) \ + __get_user_asm(x, addr, err, ldrh) + +#else + #ifndef __ARMEB__ #define __get_user_asm_half(x, __gu_addr, err) \ ({ \ @@ -397,6 +404,8 @@ do { \ }) #endif +#endif /* __LINUX_ARM_ARCH__ >= 6 */ + #define __get_user_asm_word(x, addr, err) \ __get_user_asm(x, addr, err, ldr) #endif @@ -472,6 +481,13 @@ do { \ #define __put_user_asm_byte(x, __pu_addr, err) \ __put_user_asm(x, __pu_addr, err, strb) +#if __LINUX_ARM_ARCH__ >= 6 + +#define __put_user_asm_half(x, __pu_addr, err) \ + __put_user_asm(x, __pu_addr, err, strh) + +#else + #ifndef __ARMEB__ #define __put_user_asm_half(x, __pu_addr, err) \ ({ \ @@ -488,6 +504,8 @@ do { \ }) #endif +#endif /* __LINUX_ARM_ARCH__ >= 6 */ + #define __put_user_asm_word(x, __pu_addr, err) \ __put_user_asm(x, __pu_addr, err, str) -- cgit v1.2.3