[PATCH 1/4] riscv: implement user_access_begin and families

Jisheng Zhang
2024-06-25T04:19:19Z

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>
---
arch/riscv/include/asm/uaccess.h | 63 ++++++++++++++++++++++++++++++++
1 file changed, 63 insertions(+)

diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index 72ec1d9bd3f3..09d4ca37522c 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -28,6 +28,19 @@
#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
@@ -335,6 +348,56 @@ 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(a,b) user_access_begin(a,b)
+#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) { }
+
+#define unsafe_put_user(x, ptr, label) do { \
+ long __kr_err = 0; \
+ __put_user_nocheck(x, (ptr), __kr_err); \
+ if (__kr_err) goto label; \
+} while (0)
+
+#define unsafe_get_user(x, ptr, label) do { \
+ long __kr_err = 0; \
+ __inttype(*(ptr)) __gu_val; \
+ __get_user_nocheck(__gu_val, (ptr), __kr_err); \
+ (x) = (__force __typeof__(*(ptr)))__gu_val; \
+ if (__kr_err) goto label; \
+} while (0)
+
+/*
+ * We want the unsafe accessors to always be inlined and use
+ * the error labels - thus the macro games.
+ */
+#define unsafe_copy_loop(dst, src, len, type, label) \
+ while (len >= sizeof(type)) { \
+ unsafe_put_user(*(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, label); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label); \
+} while (0)
+
#else /* CONFIG_MMU */
#include <asm-generic/uaccess.h>
#endif /* CONFIG_MMU */
--
2.43.0