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/m68k/include/asm/uaccess.h

@@ -10,20 +10,7 @@
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <asm/extable.h>
-
-/* We let the MMU do all checking */
-static inline int access_ok(const void __user *ptr,
-			    unsigned long size)
-{
-	unsigned long limit = TASK_SIZE;
-	unsigned long addr = (unsigned long)ptr;
-
-	if (IS_ENABLED(CONFIG_CPU_HAS_ADDRESS_SPACES) ||
-	    !IS_ENABLED(CONFIG_MMU))
-		return 1;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
+#include <asm-generic/access_ok.h>
 
 /*
  * Not all varients of the 68k family support the notion of address spaces.