Unverified Commit 19500c6d authored by Jisheng Zhang's avatar Jisheng Zhang Committed by Palmer Dabbelt
Browse files

riscv: implement user_access_begin() and families 



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: default avatarJisheng Zhang <jszhang@kernel.org>
Signed-off-by: default avatarCyril Bur <cyrilbur@tenstorrent.com>
Reviewed-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250410070526.3160847-3-cyrilbur@tenstorrent.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 788aa64c

arch/riscv/include/asm/uaccess.h

+76 −0
Original line number Diff line number Diff line
@@ -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 */