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riscv: implement user_access_begin() and families

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Currently, when a function like strncpy_from_user() is called,
the userspace access protection is disabled and enabled
for every word read.

By implementing user_access_begin() and families, the protection
is disabled at the beginning of the copy and enabled at the end.

The __inttype macro is borrowed from x86 implementation.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Cyril Bur <cyrilbur@tenstorrent.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250410070526.3160847-3-cyrilbur@tenstorrent.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Jisheng Zhang 2025-04-10 07:05:23 +00:00 committed by Palmer Dabbelt
parent 788aa64c01
commit 19500c6dbc
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1 changed files with 76 additions and 0 deletions
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76
arch/riscv/include/asm/uaccess.h
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@ -61,6 +61,19 @@ static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigne
#define __disable_user_access() \
__asm__ __volatile__ ("csrc sstatus, %0" : : "r" (SR_SUM) : "memory")
/*
* This is the smallest unsigned integer type that can fit a value
* (up to 'long long')
*/
#define __inttype(x) __typeof__( \
__typefits(x, char, \
__typefits(x, short, \
__typefits(x, int, \
__typefits(x, long, 0ULL)))))
#define __typefits(x, type, not) \
__builtin_choose_expr(sizeof(x) <= sizeof(type), (unsigned type)0, not)
/*
* The exception table consists of pairs of addresses: the first is the
* address of an instruction that is allowed to fault, and the second is
@ -368,6 +381,69 @@ do { \
goto err_label; \
} while (0)
static __must_check __always_inline bool user_access_begin(const void __user *ptr, size_t len)
{
if (unlikely(!access_ok(ptr, len)))
return 0;
__enable_user_access();
return 1;
}
#define user_access_begin user_access_begin
#define user_access_end __disable_user_access
static inline unsigned long user_access_save(void) { return 0UL; }
static inline void user_access_restore(unsigned long enabled) { }
/*
* We want the unsafe accessors to always be inlined and use
* the error labels - thus the macro games.
*/
#define unsafe_put_user(x, ptr, label) do { \
long __err = 0; \
__put_user_nocheck(x, (ptr), __err); \
if (__err) \
goto label; \
} while (0)
#define unsafe_get_user(x, ptr, label) do { \
long __err = 0; \
__inttype(*(ptr)) __gu_val; \
__get_user_nocheck(__gu_val, (ptr), __err); \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
if (__err) \
goto label; \
} while (0)
#define unsafe_copy_loop(dst, src, len, type, op, label) \
while (len >= sizeof(type)) { \
op(*(type *)(src), (type __user *)(dst), label); \
dst += sizeof(type); \
src += sizeof(type); \
len -= sizeof(type); \
}
#define unsafe_copy_to_user(_dst, _src, _len, label) \
do { \
char __user *__ucu_dst = (_dst); \
const char *__ucu_src = (_src); \
size_t __ucu_len = (_len); \
unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, unsafe_put_user, label); \
unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, unsafe_put_user, label); \
unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, unsafe_put_user, label); \
unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, unsafe_put_user, label); \
} while (0)
#define unsafe_copy_from_user(_dst, _src, _len, label) \
do { \
char *__ucu_dst = (_dst); \
const char __user *__ucu_src = (_src); \
size_t __ucu_len = (_len); \
unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u64, unsafe_get_user, label); \
unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u32, unsafe_get_user, label); \
unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u16, unsafe_get_user, label); \
unsafe_copy_loop(__ucu_src, __ucu_dst, __ucu_len, u8, unsafe_get_user, label); \
} while (0)
#else /* CONFIG_MMU */
#include <asm-generic/uaccess.h>
#endif /* CONFIG_MMU */