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SubjectRe: [PATCH v3] ARM: add get_user() support for 8 byte types
On Thu, Jun 12, 2014 at 04:42:35PM +0100, Daniel Thompson wrote:
> A new atomic modeset/pageflip ioctl being developed in DRM requires
> get_user() to work for 64bit types (in addition to just put_user()).
>
> v1: original
> v2: pass correct size to check_uaccess, and better handling of narrowing
> double word read with __get_user_xb() (Russell King's suggestion)
> v3: fix a couple of checkpatch issues

This is still unsafe.

> #define __get_user_check(x,p) \
> ({ \
> unsigned long __limit = current_thread_info()->addr_limit - 1; \
> register const typeof(*(p)) __user *__p asm("r0") = (p);\
> - register unsigned long __r2 asm("r2"); \
> + register typeof(x) __r2 asm("r2"); \

So, __r2 becomes the type of 'x'. If 'x' is a 64-bit type, and *p is
an 8-bit, 16-bit, or 32-bit type, this fails horribly by leaving the
upper word of __r2 undefined.

__r2 must follow the size of the value we are reading. I think the
last solution which was proposed was this:

arch/arm/include/asm/uaccess.h | 17 +++++++++++++----
arch/arm/lib/getuser.S | 33 ++++++++++++++++++++++++++++++++-
2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 72abdc5..747f2cb 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -93,6 +93,9 @@ static inline void set_fs(mm_segment_t fs)
: "cc"); \
flag; })

+#define __inttype(x) \
+ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
+
/*
* Single-value transfer routines. They automatically use the right
* size if we just have the right pointer type. Note that the functions
@@ -107,14 +110,16 @@ static inline void set_fs(mm_segment_t fs)
extern int __get_user_1(void *);
extern int __get_user_2(void *);
extern int __get_user_4(void *);
+extern int __get_user_8(void *);

-#define __GUP_CLOBBER_1 "lr", "cc"
+#define __GUP_CLOBBER_1 "lr", "cc"
#ifdef CONFIG_CPU_USE_DOMAINS
-#define __GUP_CLOBBER_2 "ip", "lr", "cc"
+#define __GUP_CLOBBER_2 "ip", "lr", "cc"
#else
#define __GUP_CLOBBER_2 "lr", "cc"
#endif
-#define __GUP_CLOBBER_4 "lr", "cc"
+#define __GUP_CLOBBER_4 "lr", "cc"
+#define __GUP_CLOBBER_8 "lr", "cc"

#define __get_user_x(__r2,__p,__e,__l,__s) \
__asm__ __volatile__ ( \
@@ -129,7 +134,7 @@ extern int __get_user_4(void *);
({ \
unsigned long __limit = current_thread_info()->addr_limit - 1; \
register const typeof(*(p)) __user *__p asm("r0") = (p);\
- register unsigned long __r2 asm("r2"); \
+ register __inttype(*p) __r2 asm("r2"); \
register unsigned long __l asm("r1") = __limit; \
register int __e asm("r0"); \
switch (sizeof(*(__p))) { \
@@ -142,6 +147,9 @@ extern int __get_user_4(void *);
case 4: \
__get_user_x(__r2, __p, __e, __l, 4); \
break; \
+ case 8: \
+ __get_user_x(__r2, __p, __e, __l, 8); \
+ break; \
default: __e = __get_user_bad(); break; \
} \
x = (typeof(*(p))) __r2; \
@@ -150,6 +158,7 @@ extern int __get_user_4(void *);

#define get_user(x,p) \
({ \
+ __chk_user_ptr(ptr); \
might_fault(); \
__get_user_check(x,p); \
})
diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S
index 9b06bb4..3583c83 100644
--- a/arch/arm/lib/getuser.S
+++ b/arch/arm/lib/getuser.S
@@ -18,7 +18,7 @@
* Inputs: r0 contains the address
* r1 contains the address limit, which must be preserved
* Outputs: r0 is the error code
- * r2 contains the zero-extended value
+ * r2/r3 contains the zero-extended value
* lr corrupted
*
* No other registers must be altered. (see <asm/uaccess.h>
@@ -32,6 +32,14 @@
#include <asm/errno.h>
#include <asm/domain.h>

+#ifdef __ARMEB__
+#define rlo8 r3
+#define rhi8 r2
+#else
+#define rlo8 r2
+#define rhi8 r3
+#endif
+
ENTRY(__get_user_1)
check_uaccess r0, 1, r1, r2, __get_user_bad
1: TUSER(ldrb) r2, [r0]
@@ -66,15 +74,38 @@ ENTRY(__get_user_4)
mov pc, lr
ENDPROC(__get_user_4)

+ENTRY(__get_user_8)
+ check_uaccess r0, 4, r1, r2, __get_user_bad8
+#ifdef CONFIG_CPU_USE_DOMAINS
+#define GU8_FIXUPS 5b, 6b
+5: ldrt rlo8, [r0], #4
+6: ldrt rhi8, [r0], #0
+#elif __LINUX_ARM_ARCH__ >= 6
+#define GU8_FIXUPS 5b
+5: ldrd r2, [r0]
+#else
+#define GU8_FIXUPS 5b, 6b
+5: ldr rlo8, [r0, #0]
+6: ldr rhi8, [r0, #4]
+#endif
+ mov r0, #0
+ mov pc, lr
+
+__get_user_bad8:
+ mov r3, #0
__get_user_bad:
mov r2, #0
mov r0, #-EFAULT
mov pc, lr
ENDPROC(__get_user_bad)
+ENDPROC(__get_user_bad8)

.pushsection __ex_table, "a"
.long 1b, __get_user_bad
.long 2b, __get_user_bad
.long 3b, __get_user_bad
.long 4b, __get_user_bad
+ .irp param, GU8_FIXUPS
+ .long \param, __get_user_bad8
+ .endr
.popsection

--
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