[PATCH v2 6/6] powerpc: Implement user_access_begin and friends

Christophe Leroy
2020-01-22T17:53:02Z

Today, when a function like strncpy_from_user() is called,
the userspace access protection is de-activated and re-activated
for every word read.

By implementing user_access_begin and friends, the protection
is de-activated at the beginning of the copy and re-activated at the
end.

Implement user_access_begin(), user_access_end() and
unsafe_get_user(), unsafe_put_user() and unsafe_copy_to_user()

For the time being, we keep user_access_save() and
user_access_restore() as nops.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
v2: no change
---
arch/powerpc/include/asm/uaccess.h | 92 ++++++++++++++++++++++++++----
1 file changed, 82 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index cafad1960e76..ea67bbd56bd4 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -91,9 +91,14 @@ static inline int __access_ok(unsigned long addr, unsigned long size,
__put_user_check((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))

#define __get_user(x, ptr) \
- __get_user_nocheck((x), (ptr), sizeof(*(ptr)))
+ __get_user_nocheck((x), (ptr), sizeof(*(ptr)), true)
#define __put_user(x, ptr) \
- __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
+ __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)), true)
+
+#define __get_user_allowed(x, ptr) \
+ __get_user_nocheck((x), (ptr), sizeof(*(ptr)), false)
+#define __put_user_allowed(x, ptr) \
+ __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)), false)

#define __get_user_inatomic(x, ptr) \
__get_user_nosleep((x), (ptr), sizeof(*(ptr)))
@@ -138,10 +143,9 @@ extern long __put_user_bad(void);
: "r" (x), "b" (addr), "i" (-EFAULT), "0" (err))
#endif /* __powerpc64__ */

-#define __put_user_size(x, ptr, size, retval) \
+#define __put_user_size_allowed(x, ptr, size, retval) \
do { \
retval = 0; \
- allow_write_to_user(ptr, size); \
switch (size) { \
case 1: __put_user_asm(x, ptr, retval, "stb"); break; \
case 2: __put_user_asm(x, ptr, retval, "sth"); break; \
@@ -149,17 +153,26 @@ do { \
case 8: __put_user_asm2(x, ptr, retval); break; \
default: __put_user_bad(); \
} \
+} while (0)
+
+#define __put_user_size(x, ptr, size, retval) \
+do { \
+ allow_write_to_user(ptr, size); \
+ __put_user_size_allowed(x, ptr, size, retval); \
prevent_write_to_user(ptr, size); \
} while (0)

-#define __put_user_nocheck(x, ptr, size) \
+#define __put_user_nocheck(x, ptr, size, allow) \
({ \
long __pu_err; \
__typeof__(*(ptr)) __user *__pu_addr = (ptr); \
if (!is_kernel_addr((unsigned long)__pu_addr)) \
might_fault(); \
__chk_user_ptr(ptr); \
- __put_user_size((x), __pu_addr, (size), __pu_err); \
+ if (allow) \
+ __put_user_size((x), __pu_addr, (size), __pu_err); \
+ else \
+ __put_user_size_allowed((x), __pu_addr, (size), __pu_err); \
__pu_err; \
})

@@ -236,13 +249,12 @@ extern long __get_user_bad(void);
: "b" (addr), "i" (-EFAULT), "0" (err))
#endif /* __powerpc64__ */

-#define __get_user_size(x, ptr, size, retval) \
+#define __get_user_size_allowed(x, ptr, size, retval) \
do { \
retval = 0; \
__chk_user_ptr(ptr); \
if (size > sizeof(x)) \
(x) = __get_user_bad(); \
- allow_read_from_user(ptr, size); \
switch (size) { \
case 1: __get_user_asm(x, ptr, retval, "lbz"); break; \
case 2: __get_user_asm(x, ptr, retval, "lhz"); break; \
@@ -250,6 +262,12 @@ do { \
case 8: __get_user_asm2(x, ptr, retval); break; \
default: (x) = __get_user_bad(); \
} \
+} while (0)
+
+#define __get_user_size(x, ptr, size, retval) \
+do { \
+ allow_read_from_user(ptr, size); \
+ __get_user_size_allowed(x, ptr, size, retval); \
prevent_read_from_user(ptr, size); \
} while (0)

@@ -260,7 +278,7 @@ do { \
#define __long_type(x) \
__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))

-#define __get_user_nocheck(x, ptr, size) \
+#define __get_user_nocheck(x, ptr, size, allow) \
({ \
long __gu_err; \
__long_type(*(ptr)) __gu_val; \
@@ -269,7 +287,10 @@ do { \
if (!is_kernel_addr((unsigned long)__gu_addr)) \
might_fault(); \
barrier_nospec(); \
- __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \
+ if (allow) \
+ __get_user_size(__gu_val, __gu_addr, (size), __gu_err); \
+ else \
+ __get_user_size_allowed(__gu_val, __gu_addr, (size), __gu_err); \
(x) = (__typeof__(*(ptr)))__gu_val; \
__gu_err; \
})
@@ -387,6 +408,34 @@ static inline unsigned long raw_copy_to_user(void __user *to,
return ret;
}

+static inline unsigned long
+raw_copy_to_user_allowed(void __user *to, const void *from, unsigned long n)
+{
+ unsigned long ret;
+ if (__builtin_constant_p(n) && (n) <= 8) {
+ ret = 1;
+
+ switch (n) {
+ case 1:
+ __put_user_size_allowed(*(u8 *)from, (u8 __user *)to, 1, ret);
+ break;
+ case 2:
+ __put_user_size_allowed(*(u16 *)from, (u16 __user *)to, 2, ret);
+ break;
+ case 4:
+ __put_user_size_allowed(*(u32 *)from, (u32 __user *)to, 4, ret);
+ break;
+ case 8:
+ __put_user_size_allowed(*(u64 *)from, (u64 __user *)to, 8, ret);
+ break;
+ }
+ if (ret == 0)
+ return 0;
+ }
+
+ return __copy_tofrom_user(to, (__force const void __user *)from, n);
+}
+
static __always_inline unsigned long __must_check
copy_to_user_mcsafe(void __user *to, const void *from, unsigned long n)
{
@@ -428,4 +477,27 @@ extern long __copy_from_user_flushcache(void *dst, const void __user *src,
extern void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
size_t len);

+static __must_check inline bool user_access_begin(const void __user *ptr, size_t len)
+{
+ if (unlikely(!access_ok(ptr, len)))
+ return false;
+ allow_read_write_user((void __user *)ptr, ptr, len);
+ return true;
+}
+#define user_access_begin user_access_begin
+
+static inline void user_access_end(void)
+{
+ prevent_user_access(NULL, NULL, ~0UL, KUAP_SELF);
+}
+#define user_access_end user_access_end
+
+static inline unsigned long user_access_save(void) { return 0UL; }
+static inline void user_access_restore(unsigned long flags) { }
+
+#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
+#define unsafe_get_user(x,p,e) unsafe_op_wrap(__get_user_allowed(x,p),e)
+#define unsafe_put_user(x,p,e) unsafe_op_wrap(__put_user_allowed(x,p),e)
+#define unsafe_copy_to_user(d,s,l,e) unsafe_op_wrap(raw_copy_to_user_allowed(d,s,l),e)
+
#endif /* _ARCH_POWERPC_UACCESS_H */
--
2.25.0