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 <vincent.whitchurch@axis.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S
index 746e780..b2e4bc3a 100644
--- a/arch/arm/lib/getuser.S
+++ b/arch/arm/lib/getuser.S
@@ -42,6 +42,12 @@
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 @@
#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 @@
.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