Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit b8252ec6 authored by Vincent Whitchurch's avatar Vincent Whitchurch Committed by Greg Kroah-Hartman
Browse files

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: default avatarVincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent d0426a34

arch/arm/include/asm/uaccess.h

+18 −0
Original line number Diff line number Diff line
@@ -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)

arch/arm/lib/getuser.S

+11 −0
Original line number Diff line number Diff line
@@ -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

arch/arm/lib/putuser.S

+10 −10
Original line number Diff line number Diff line
@@ -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