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powerpc: Implement user_access_begin and friends
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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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/36d4fbf9e56a75994aca4ee2214c77b26a5a8d35.1579866752.git.christophe.leroy@c-s.fr
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Christophe Leroy authored and Michael Ellerman committed Jan 28, 2020
1 parent bedb4db commit 5cd6233
Showing 1 changed file with 66 additions and 19 deletions.
85 changes: 66 additions & 19 deletions arch/powerpc/include/asm/uaccess.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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)))
Expand Down Expand Up @@ -138,28 +143,36 @@ 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; \
case 4: __put_user_asm(x, ptr, retval, "stw"); break; \
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, do_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 (do_allow) \
__put_user_size((x), __pu_addr, (size), __pu_err); \
else \
__put_user_size_allowed((x), __pu_addr, (size), __pu_err); \
__pu_err; \
})

Expand Down Expand Up @@ -236,20 +249,25 @@ 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; \
case 4: __get_user_asm(x, ptr, retval, "lwz"); break; \
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)

Expand All @@ -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, do_allow) \
({ \
long __gu_err; \
__long_type(*(ptr)) __gu_val; \
Expand All @@ -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 (do_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; \
})
Expand Down Expand Up @@ -356,33 +377,40 @@ static inline unsigned long raw_copy_from_user(void *to,
return ret;
}

static inline unsigned long raw_copy_to_user(void __user *to,
const void *from, unsigned long n)
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;
unsigned long ret = 1;

switch (n) {
case 1:
__put_user_size(*(u8 *)from, (u8 __user *)to, 1, ret);
__put_user_size_allowed(*(u8 *)from, (u8 __user *)to, 1, ret);
break;
case 2:
__put_user_size(*(u16 *)from, (u16 __user *)to, 2, ret);
__put_user_size_allowed(*(u16 *)from, (u16 __user *)to, 2, ret);
break;
case 4:
__put_user_size(*(u32 *)from, (u32 __user *)to, 4, ret);
__put_user_size_allowed(*(u32 *)from, (u32 __user *)to, 4, ret);
break;
case 8:
__put_user_size(*(u64 *)from, (u64 __user *)to, 8, ret);
__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 inline unsigned long
raw_copy_to_user(void __user *to, const void *from, unsigned long n)
{
unsigned long ret;

allow_write_to_user(to, n);
ret = __copy_tofrom_user(to, (__force const void __user *)from, n);
ret = raw_copy_to_user_allowed(to, from, n);
prevent_write_to_user(to, n);
return ret;
}
Expand Down Expand Up @@ -428,4 +456,23 @@ 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
#define user_access_end prevent_current_access_user

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 */

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