[PATCH 7/9] ARM: uaccess: provide uaccess_save_and_enable() and uaccess_restore()
Russell King
rmk+kernel at arm.linux.org.uk
Fri Aug 21 06:31:46 PDT 2015
Provide uaccess_save_and_enable() and uaccess_restore() to permit
control of userspace visibility to the kernel, and hook these into
the appropriate places in the kernel where we need to access
userspace.
Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
arch/arm/include/asm/futex.h | 19 ++++++++--
arch/arm/include/asm/uaccess.h | 71 +++++++++++++++++++++++++++++++++++---
arch/arm/kernel/armksyms.c | 6 ++--
arch/arm/lib/clear_user.S | 6 ++--
arch/arm/lib/copy_from_user.S | 6 ++--
arch/arm/lib/copy_to_user.S | 6 ++--
arch/arm/lib/uaccess_with_memcpy.c | 4 +--
7 files changed, 97 insertions(+), 21 deletions(-)
diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 5eed82809d82..6795368ad023 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -22,8 +22,11 @@
#ifdef CONFIG_SMP
#define __futex_atomic_op(insn, ret, oldval, tmp, uaddr, oparg) \
+({ \
+ unsigned int __ua_flags; \
smp_mb(); \
prefetchw(uaddr); \
+ __ua_flags = uaccess_save_and_enable(); \
__asm__ __volatile__( \
"1: ldrex %1, [%3]\n" \
" " insn "\n" \
@@ -34,12 +37,15 @@
__futex_atomic_ex_table("%5") \
: "=&r" (ret), "=&r" (oldval), "=&r" (tmp) \
: "r" (uaddr), "r" (oparg), "Ir" (-EFAULT) \
- : "cc", "memory")
+ : "cc", "memory"); \
+ uaccess_restore(__ua_flags); \
+})
static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
u32 oldval, u32 newval)
{
+ unsigned int __ua_flags;
int ret;
u32 val;
@@ -49,6 +55,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
smp_mb();
/* Prefetching cannot fault */
prefetchw(uaddr);
+ __ua_flags = uaccess_save_and_enable();
__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
"1: ldrex %1, [%4]\n"
" teq %1, %2\n"
@@ -61,6 +68,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
: "=&r" (ret), "=&r" (val)
: "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
: "cc", "memory");
+ uaccess_restore(__ua_flags);
smp_mb();
*uval = val;
@@ -73,6 +81,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
#include <asm/domain.h>
#define __futex_atomic_op(insn, ret, oldval, tmp, uaddr, oparg) \
+({ \
+ unsigned int __ua_flags = uaccess_save_and_enable(); \
__asm__ __volatile__( \
"1: " TUSER(ldr) " %1, [%3]\n" \
" " insn "\n" \
@@ -81,12 +91,15 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
__futex_atomic_ex_table("%5") \
: "=&r" (ret), "=&r" (oldval), "=&r" (tmp) \
: "r" (uaddr), "r" (oparg), "Ir" (-EFAULT) \
- : "cc", "memory")
+ : "cc", "memory"); \
+ uaccess_restore(__ua_flags); \
+})
static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
u32 oldval, u32 newval)
{
+ unsigned int __ua_flags;
int ret = 0;
u32 val;
@@ -94,6 +107,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
return -EFAULT;
preempt_disable();
+ __ua_flags = uaccess_save_and_enable();
__asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
"1: " TUSER(ldr) " %1, [%4]\n"
" teq %1, %2\n"
@@ -103,6 +117,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
: "+r" (ret), "=&r" (val)
: "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
: "cc", "memory");
+ uaccess_restore(__ua_flags);
*uval = val;
preempt_enable();
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 74b17d09ef7a..4ae10967a8ba 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -94,6 +94,21 @@ static inline void set_fs(mm_segment_t fs)
flag; })
/*
+ * These two functions allow hooking accesses to userspace to increase
+ * system integrity by ensuring that the kernel can not inadvertantly
+ * perform such accesses (eg, via list poison values) which could then
+ * be exploited for priviledge escalation.
+ */
+static inline unsigned int uaccess_save_and_enable(void)
+{
+ return 0;
+}
+
+static inline void uaccess_restore(unsigned int flags)
+{
+}
+
+/*
* Single-value transfer routines. They automatically use the right
* size if we just have the right pointer type. Note that the functions
* which read from user space (*get_*) need to take care not to leak
@@ -165,6 +180,7 @@ extern int __get_user_64t_4(void *);
register typeof(x) __r2 asm("r2"); \
register unsigned long __l asm("r1") = __limit; \
register int __e asm("r0"); \
+ unsigned int __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(__p))) { \
case 1: \
if (sizeof((x)) >= 8) \
@@ -192,6 +208,7 @@ extern int __get_user_64t_4(void *);
break; \
default: __e = __get_user_bad(); break; \
} \
+ uaccess_restore(__ua_flags); \
x = (typeof(*(p))) __r2; \
__e; \
})
@@ -224,6 +241,7 @@ extern int __put_user_8(void *, unsigned long long);
register const typeof(*(p)) __user *__p asm("r0") = __tmp_p; \
register unsigned long __l asm("r1") = __limit; \
register int __e asm("r0"); \
+ unsigned int __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(__p))) { \
case 1: \
__put_user_x(__r2, __p, __e, __l, 1); \
@@ -239,6 +257,7 @@ extern int __put_user_8(void *, unsigned long long);
break; \
default: __e = __put_user_bad(); break; \
} \
+ uaccess_restore(__ua_flags); \
__e; \
})
@@ -300,14 +319,17 @@ static inline void set_fs(mm_segment_t fs)
do { \
unsigned long __gu_addr = (unsigned long)(ptr); \
unsigned long __gu_val; \
+ unsigned int __ua_flags; \
__chk_user_ptr(ptr); \
might_fault(); \
+ __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(ptr))) { \
case 1: __get_user_asm_byte(__gu_val, __gu_addr, err); break; \
case 2: __get_user_asm_half(__gu_val, __gu_addr, err); break; \
case 4: __get_user_asm_word(__gu_val, __gu_addr, err); break; \
default: (__gu_val) = __get_user_bad(); \
} \
+ uaccess_restore(__ua_flags); \
(x) = (__typeof__(*(ptr)))__gu_val; \
} while (0)
@@ -381,9 +403,11 @@ do { \
#define __put_user_err(x, ptr, err) \
do { \
unsigned long __pu_addr = (unsigned long)(ptr); \
+ unsigned int __ua_flags; \
__typeof__(*(ptr)) __pu_val = (x); \
__chk_user_ptr(ptr); \
might_fault(); \
+ __ua_flags = uaccess_save_and_enable(); \
switch (sizeof(*(ptr))) { \
case 1: __put_user_asm_byte(__pu_val, __pu_addr, err); break; \
case 2: __put_user_asm_half(__pu_val, __pu_addr, err); break; \
@@ -391,6 +415,7 @@ do { \
case 8: __put_user_asm_dword(__pu_val, __pu_addr, err); break; \
default: __put_user_bad(); \
} \
+ uaccess_restore(__ua_flags); \
} while (0)
#define __put_user_asm_byte(x, __pu_addr, err) \
@@ -474,11 +499,46 @@ do { \
#ifdef CONFIG_MMU
-extern unsigned long __must_check __copy_from_user(void *to, const void __user *from, unsigned long n);
-extern unsigned long __must_check __copy_to_user(void __user *to, const void *from, unsigned long n);
-extern unsigned long __must_check __copy_to_user_std(void __user *to, const void *from, unsigned long n);
-extern unsigned long __must_check __clear_user(void __user *addr, unsigned long n);
-extern unsigned long __must_check __clear_user_std(void __user *addr, unsigned long n);
+extern unsigned long __must_check
+arm_copy_from_user(void *to, const void __user *from, unsigned long n);
+
+static inline unsigned long __must_check
+__copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+ unsigned int __ua_flags = uaccess_save_and_enable();
+ n = arm_copy_from_user(to, from, n);
+ uaccess_restore(__ua_flags);
+ return n;
+}
+
+extern unsigned long __must_check
+arm_copy_to_user(void __user *to, const void *from, unsigned long n);
+extern unsigned long __must_check
+__copy_to_user_std(void __user *to, const void *from, unsigned long n);
+
+static inline unsigned long __must_check
+__copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+ unsigned int __ua_flags = uaccess_save_and_enable();
+ n = arm_copy_to_user(to, from, n);
+ uaccess_restore(__ua_flags);
+ return n;
+}
+
+extern unsigned long __must_check
+arm_clear_user(void __user *addr, unsigned long n);
+extern unsigned long __must_check
+__clear_user_std(void __user *addr, unsigned long n);
+
+static inline unsigned long __must_check
+__clear_user(void __user *addr, unsigned long n)
+{
+ unsigned int __ua_flags = uaccess_save_and_enable();
+ n = arm_clear_user(addr, n);
+ uaccess_restore(__ua_flags);
+ return n;
+}
+
#else
#define __copy_from_user(to, from, n) (memcpy(to, (void __force *)from, n), 0)
#define __copy_to_user(to, from, n) (memcpy((void __force *)to, from, n), 0)
@@ -511,6 +571,7 @@ static inline unsigned long __must_check clear_user(void __user *to, unsigned lo
return n;
}
+/* These are from lib/ code, and use __get_user() and friends */
extern long strncpy_from_user(char *dest, const char __user *src, long count);
extern __must_check long strlen_user(const char __user *str);
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index a88671cfe1ff..a35d72d30b56 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -91,9 +91,9 @@ EXPORT_SYMBOL(__memzero);
#ifdef CONFIG_MMU
EXPORT_SYMBOL(copy_page);
-EXPORT_SYMBOL(__copy_from_user);
-EXPORT_SYMBOL(__copy_to_user);
-EXPORT_SYMBOL(__clear_user);
+EXPORT_SYMBOL(arm_copy_from_user);
+EXPORT_SYMBOL(arm_copy_to_user);
+EXPORT_SYMBOL(arm_clear_user);
EXPORT_SYMBOL(__get_user_1);
EXPORT_SYMBOL(__get_user_2);
diff --git a/arch/arm/lib/clear_user.S b/arch/arm/lib/clear_user.S
index 1710fd7db2d5..970d6c043774 100644
--- a/arch/arm/lib/clear_user.S
+++ b/arch/arm/lib/clear_user.S
@@ -12,14 +12,14 @@
.text
-/* Prototype: int __clear_user(void *addr, size_t sz)
+/* Prototype: unsigned long arm_clear_user(void *addr, size_t sz)
* Purpose : clear some user memory
* Params : addr - user memory address to clear
* : sz - number of bytes to clear
* Returns : number of bytes NOT cleared
*/
ENTRY(__clear_user_std)
-WEAK(__clear_user)
+WEAK(arm_clear_user)
stmfd sp!, {r1, lr}
mov r2, #0
cmp r1, #4
@@ -44,7 +44,7 @@ WEAK(__clear_user)
USER( strnebt r2, [r0])
mov r0, #0
ldmfd sp!, {r1, pc}
-ENDPROC(__clear_user)
+ENDPROC(arm_clear_user)
ENDPROC(__clear_user_std)
.pushsection .text.fixup,"ax"
diff --git a/arch/arm/lib/copy_from_user.S b/arch/arm/lib/copy_from_user.S
index 7a235b9952be..1512bebfbf1b 100644
--- a/arch/arm/lib/copy_from_user.S
+++ b/arch/arm/lib/copy_from_user.S
@@ -17,7 +17,7 @@
/*
* Prototype:
*
- * size_t __copy_from_user(void *to, const void *from, size_t n)
+ * size_t arm_copy_from_user(void *to, const void *from, size_t n)
*
* Purpose:
*
@@ -89,11 +89,11 @@
.text
-ENTRY(__copy_from_user)
+ENTRY(arm_copy_from_user)
#include "copy_template.S"
-ENDPROC(__copy_from_user)
+ENDPROC(arm_copy_from_user)
.pushsection .fixup,"ax"
.align 0
diff --git a/arch/arm/lib/copy_to_user.S b/arch/arm/lib/copy_to_user.S
index 9648b0675a3e..caf5019d8161 100644
--- a/arch/arm/lib/copy_to_user.S
+++ b/arch/arm/lib/copy_to_user.S
@@ -17,7 +17,7 @@
/*
* Prototype:
*
- * size_t __copy_to_user(void *to, const void *from, size_t n)
+ * size_t arm_copy_to_user(void *to, const void *from, size_t n)
*
* Purpose:
*
@@ -93,11 +93,11 @@
.text
ENTRY(__copy_to_user_std)
-WEAK(__copy_to_user)
+WEAK(arm_copy_to_user)
#include "copy_template.S"
-ENDPROC(__copy_to_user)
+ENDPROC(arm_copy_to_user)
ENDPROC(__copy_to_user_std)
.pushsection .text.fixup,"ax"
diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
index 3e58d710013c..77f020e75ccd 100644
--- a/arch/arm/lib/uaccess_with_memcpy.c
+++ b/arch/arm/lib/uaccess_with_memcpy.c
@@ -136,7 +136,7 @@ __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
}
unsigned long
-__copy_to_user(void __user *to, const void *from, unsigned long n)
+arm_copy_to_user(void __user *to, const void *from, unsigned long n)
{
/*
* This test is stubbed out of the main function above to keep
@@ -190,7 +190,7 @@ __clear_user_memset(void __user *addr, unsigned long n)
return n;
}
-unsigned long __clear_user(void __user *addr, unsigned long n)
+unsigned long arm_clear_user(void __user *addr, unsigned long n)
{
/* See rational for this in __copy_to_user() above. */
if (n < 64)
--
2.1.0
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