From: Vincent Whitchurch vincent.whitchurch@axis.com
[ 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 vincent.whitchurch@axis.com Signed-off-by: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/include/asm/uaccess.h | 18 ++++++++++++++++++ arch/arm/lib/getuser.S | 11 +++++++++++ arch/arm/lib/putuser.S | 20 ++++++++++---------- 3 files changed, 39 insertions(+), 10 deletions(-)
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h index c136eef8f690b..6390a40f16e73 100644 --- a/arch/arm/include/asm/uaccess.h +++ b/arch/arm/include/asm/uaccess.h @@ -349,6 +349,13 @@ 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) \ ({ \ @@ -367,6 +374,8 @@ do { \ }) #endif
+#endif /* __LINUX_ARM_ARCH__ >= 6 */ + #define __get_user_asm_word(x, addr, err) \ __get_user_asm(x, addr, err, ldr) #endif @@ -442,6 +451,13 @@ 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) \ ({ \ @@ -458,6 +474,8 @@ do { \ }) #endif
+#endif /* __LINUX_ARM_ARCH__ >= 6 */ + #define __put_user_asm_word(x, __pu_addr, err) \ __put_user_asm(x, __pu_addr, err, str)
diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S index 746e7801dcdf7..b2e4bc3a635e2 100644 --- a/arch/arm/lib/getuser.S +++ b/arch/arm/lib/getuser.S @@ -42,6 +42,12 @@ _ASM_NOKPROBE(__get_user_1)
ENTRY(__get_user_2) check_uaccess r0, 2, r1, r2, __get_user_bad +#if __LINUX_ARM_ARCH__ >= 6 + +2: TUSER(ldrh) r2, [r0] + +#else + #ifdef CONFIG_CPU_USE_DOMAINS rb .req ip 2: ldrbt r2, [r0], #1 @@ -56,6 +62,9 @@ rb .req r0 #else orr r2, rb, r2, lsl #8 #endif + +#endif /* __LINUX_ARM_ARCH__ >= 6 */ + mov r0, #0 ret lr ENDPROC(__get_user_2) @@ -145,7 +154,9 @@ _ASM_NOKPROBE(__get_user_bad8) .pushsection __ex_table, "a" .long 1b, __get_user_bad .long 2b, __get_user_bad +#if __LINUX_ARM_ARCH__ < 6 .long 3b, __get_user_bad +#endif .long 4b, __get_user_bad .long 5b, __get_user_bad8 .long 6b, __get_user_bad8 diff --git a/arch/arm/lib/putuser.S b/arch/arm/lib/putuser.S index 38d660d3705f4..515eeaa9975c6 100644 --- a/arch/arm/lib/putuser.S +++ b/arch/arm/lib/putuser.S @@ -41,16 +41,13 @@ ENDPROC(__put_user_1)
ENTRY(__put_user_2) check_uaccess r0, 2, r1, ip, __put_user_bad - mov ip, r2, lsr #8 -#ifdef CONFIG_THUMB2_KERNEL -#ifndef __ARMEB__ -2: TUSER(strb) r2, [r0] -3: TUSER(strb) ip, [r0, #1] +#if __LINUX_ARM_ARCH__ >= 6 + +2: TUSER(strh) r2, [r0] + #else -2: TUSER(strb) ip, [r0] -3: TUSER(strb) r2, [r0, #1] -#endif -#else /* !CONFIG_THUMB2_KERNEL */ + + mov ip, r2, lsr #8 #ifndef __ARMEB__ 2: TUSER(strb) r2, [r0], #1 3: TUSER(strb) ip, [r0] @@ -58,7 +55,8 @@ ENTRY(__put_user_2) 2: TUSER(strb) ip, [r0], #1 3: TUSER(strb) r2, [r0] #endif -#endif /* CONFIG_THUMB2_KERNEL */ + +#endif /* __LINUX_ARM_ARCH__ >= 6 */ mov r0, #0 ret lr ENDPROC(__put_user_2) @@ -91,7 +89,9 @@ ENDPROC(__put_user_bad) .pushsection __ex_table, "a" .long 1b, __put_user_bad .long 2b, __put_user_bad +#if __LINUX_ARM_ARCH__ < 6 .long 3b, __put_user_bad +#endif .long 4b, __put_user_bad .long 5b, __put_user_bad .long 6b, __put_user_bad