uaccess: generalize access_ok()

There are many different ways that access_ok() is defined across
architectures, but in the end, they all just compare against the
user_addr_max() value or they accept anything.

Provide one definition that works for most architectures, checking
against TASK_SIZE_MAX for user processes or skipping the check inside
of uaccess_kernel() sections.

For architectures without CONFIG_SET_FS(), this should be the fastest
check, as it comes down to a single comparison of a pointer against a
compile-time constant, while the architecture specific versions tend to
do something more complex for historic reasons or get something wrong.

Type checking for __user annotations is handled inconsistently across
architectures, but this is easily simplified as well by using an inline
function that takes a 'const void __user *' argument. A handful of
callers need an extra __user annotation for this.

Some architectures had trick to use 33-bit or 65-bit arithmetic on the
addresses to calculate the overflow, however this simpler version uses
fewer registers, which means it can produce better object code in the
end despite needing a second (statically predicted) branch.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mark Rutland <mark.rutland@arm.com> [arm64, asm-generic]
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Stafford Horne <shorne@gmail.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/sparc/Kconfig

@@ -62,6 +62,7 @@ config SPARC32
 
 config SPARC64
 	def_bool 64BIT
+	select ALTERNATE_USER_ADDRESS_SPACE
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_KRETPROBES

arch/sparc/include/asm/uaccess.h

@@ -10,9 +10,6 @@
 #include <asm/uaccess_32.h>
 #endif
 
-#define user_addr_max() \
-	(uaccess_kernel() ? ~0UL : TASK_SIZE)
-
 long strncpy_from_user(char *dest, const char __user *src, long count);
 
 #endif

arch/sparc/include/asm/uaccess_32.h

@@ -25,17 +25,7 @@
 #define get_fs()	(current->thread.current_ds)
 #define set_fs(val)	((current->thread.current_ds) = (val))
 
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-
-/* We have there a nice not-mapped page at PAGE_OFFSET - PAGE_SIZE, so that this test
- * can be fairly lightweight.
- * No one can read/write anything from userland in the kernel space by setting
- * large size and address near to PAGE_OFFSET - a fault will break his intentions.
- */
-#define __user_ok(addr, size) ({ (void)(size); (addr) < STACK_TOP; })
-#define __kernel_ok (uaccess_kernel())
-#define __access_ok(addr, size) (__user_ok((addr) & get_fs().seg, (size)))
-#define access_ok(addr, size) __access_ok((unsigned long)(addr), size)
+#include <asm-generic/access_ok.h>
 
 /* Uh, these should become the main single-value transfer routines..
  * They automatically use the right size if we just have the right
@@ -47,13 +37,13 @@
  * and hide all the ugliness from the user.
  */
 #define put_user(x, ptr) ({ \
-	unsigned long __pu_addr = (unsigned long)(ptr); \
+	void __user *__pu_addr = (ptr); \
 	__chk_user_ptr(ptr); \
 	__put_user_check((__typeof__(*(ptr)))(x), __pu_addr, sizeof(*(ptr))); \
 })
 
 #define get_user(x, ptr) ({ \
-	unsigned long __gu_addr = (unsigned long)(ptr); \
+	const void __user *__gu_addr = (ptr); \
 	__chk_user_ptr(ptr); \
 	__get_user_check((x), __gu_addr, sizeof(*(ptr)), __typeof__(*(ptr))); \
 })
@@ -232,7 +222,7 @@ static inline unsigned long __clear_user(void __user *addr, unsigned long size)
 
 static inline unsigned long clear_user(void __user *addr, unsigned long n)
 {
-	if (n && __access_ok((unsigned long) addr, n))
+	if (n && __access_ok(addr, n))
 		return __clear_user(addr, n);
 	else
 		return n;

arch/sparc/include/asm/uaccess_64.h

@@ -31,7 +31,7 @@
 
 #define get_fs() ((mm_segment_t){(current_thread_info()->current_ds)})
 
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
+#include <asm-generic/access_ok.h>
 
 #define set_fs(val)								\
 do {										\
@@ -61,16 +61,6 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
 	__chk_range_not_ok((unsigned long __force)(addr), size, limit); \
 })
 
-static inline int __access_ok(const void __user * addr, unsigned long size)
-{
-	return 1;
-}
-
-static inline int access_ok(const void __user * addr, unsigned long size)
-{
-	return 1;
-}
-
 void __retl_efault(void);
 
 /* Uh, these should become the main single-value transfer routines..