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>

1 files changed, 4 insertions, 7 deletions

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 199c553b740a..e8dce0cc5eaa 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -26,13 +26,7 @@
 #include <asm/memory.h>
 #include <asm/extable.h>
 
-static inline int __access_ok(const void __user *ptr, unsigned long size)
-{
-	unsigned long limit = TASK_SIZE_MAX;
-	unsigned long addr = (unsigned long)ptr;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
+static inline int __access_ok(const void __user *ptr, unsigned long size);
 
 /*
  * Test whether a block of memory is a valid user space address.
@@ -54,6 +48,9 @@ static inline int access_ok(const void __user *addr, unsigned long size)
 
 	return likely(__access_ok(addr, size));
 }
+#define access_ok access_ok
+
+#include <asm-generic/access_ok.h>
 
 /*
  * User access enabling/disabling.