[PATCH 04/14] x86: use more conventional access_ok() definition

Arnd Bergmann
2022-02-14T16:37:27Z

From: Arnd Bergmann <arnd@arndb.de>

The way that access_ok() is defined on x86 is slightly different from
most other architectures, and a bit more complex.

The generic version tends to result in the best output on all
architectures, as it results in single comparison against a constant
limit for calls with a known size.

There are a few callers of __range_not_ok(), all of which use TASK_SIZE
as the limit rather than TASK_SIZE_MAX, but I could not see any reason
for picking this. Changing these to call __access_ok() instead uses the
default limit, but keeps the behavior otherwise.

x86 is the only architecture with a WARN_ON_IN_IRQ() checking
access_ok(), but it's probably best to leave that in place.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/x86/include/asm/uaccess.h | 38 +++++++++++-----------------------
1 file changed, 12 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index ac96f9b2d64b..6956a63291b6 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -16,30 +16,13 @@
* Test whether a block of memory is a valid user space address.
* Returns 0 if the range is valid, nonzero otherwise.
*/
-static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit)
+static inline bool __access_ok(void __user *ptr, unsigned long size)
{
- /*
- * If we have used "sizeof()" for the size,
- * we know it won't overflow the limit (but
- * it might overflow the 'addr', so it's
- * important to subtract the size from the
- * limit, not add it to the address).
- */
- if (__builtin_constant_p(size))
- return unlikely(addr > limit - size);
-
- /* Arbitrary sizes? Be careful about overflow */
- addr += size;
- if (unlikely(addr < size))
- return true;
- return unlikely(addr > limit);
-}
+ unsigned long limit = TASK_SIZE_MAX;
+ unsigned long addr = ptr;

-#define __range_not_ok(addr, size, limit) \
-({ \
- __chk_user_ptr(addr); \
- __chk_range_not_ok((unsigned long __force)(addr), size, limit); \
-})
+ return (size <= limit) && (addr <= (limit - size));
+}

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
static inline bool pagefault_disabled(void);
@@ -66,12 +49,15 @@ static inline bool pagefault_disabled(void);
* Return: true (nonzero) if the memory block may be valid, false (zero)
* if it is definitely invalid.
*/
-#define access_ok(addr, size) \
-({ \
- WARN_ON_IN_IRQ(); \
- likely(!__range_not_ok(addr, size, TASK_SIZE_MAX)); \
+#define access_ok(addr, size) \
+({ \
+ WARN_ON_IN_IRQ(); \
+ likely(__access_ok(addr, size));\
})

+#define __range_not_ok(addr, size, limit) (!__access_ok(addr, size))
+#define __chk_range_not_ok(addr, size, limit) (!__access_ok((void __user *)addr, size))
+
extern int __get_user_1(void);
extern int __get_user_2(void);
extern int __get_user_4(void);
--
2.29.2