path: root/arch/arm/lib/getuser.S
diff options
authorVincent Whitchurch <vincent.whitchurch@axis.com>2018-11-09 10:12:30 +0100
committerRussell King <rmk+kernel@armlinux.org.uk>2018-11-12 10:52:04 +0000
commit344eb5539abf3e0b6ce22568c03e86450073e097 (patch)
tree7ed1b8d9e68977e903e738c518e64cecb5936b8a /arch/arm/lib/getuser.S
parentf441882a5229ffaef61a47bccd4518f7e2749cbc (diff)
ARM: 8813/1: Make aligned 2-byte getuser()/putuser() atomic on ARMv6+
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>
Diffstat (limited to 'arch/arm/lib/getuser.S')
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S
index 746e7801dcdf..b2e4bc3a635e 100644
--- a/arch/arm/lib/getuser.S
+++ b/arch/arm/lib/getuser.S
@@ -42,6 +42,12 @@ _ASM_NOKPROBE(__get_user_1)
check_uaccess r0, 2, r1, r2, __get_user_bad
+#if __LINUX_ARM_ARCH__ >= 6
+2: TUSER(ldrh) r2, [r0]
rb .req ip
2: ldrbt r2, [r0], #1
@@ -56,6 +62,9 @@ rb .req r0
orr r2, rb, r2, lsl #8
+#endif /* __LINUX_ARM_ARCH__ >= 6 */
mov r0, #0
ret lr
@@ -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
.long 4b, __get_user_bad
.long 5b, __get_user_bad8
.long 6b, __get_user_bad8