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, 1 insertions, 19 deletions

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index d20d78c34b94..2fcbec9c306c 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -56,21 +56,6 @@ extern int __put_user_bad(void);
 #ifdef CONFIG_MMU
 
 /*
- * We use 33-bit arithmetic here.  Success returns zero, failure returns
- * addr_limit.  We take advantage that addr_limit will be zero for KERNEL_DS,
- * so this will always return success in that case.
- */
-#define __range_ok(addr, size) ({ \
-	unsigned long flag, roksum; \
-	__chk_user_ptr(addr);	\
-	__asm__(".syntax unified\n" \
-		"adds %1, %2, %3; sbcscc %1, %1, %0; movcc %0, #0" \
-		: "=&r" (flag), "=&r" (roksum) \
-		: "r" (addr), "Ir" (size), "0" (TASK_SIZE) \
-		: "cc"); \
-	flag; })
-
-/*
  * This is a type: either unsigned long, if the argument fits into
  * that type, or otherwise unsigned long long.
  */
@@ -241,15 +226,12 @@ extern int __put_user_8(void *, unsigned long long);
 
 #else /* CONFIG_MMU */
 
-#define __addr_ok(addr)		((void)(addr), 1)
-#define __range_ok(addr, size)	((void)(addr), 0)
-
 #define get_user(x, p)	__get_user(x, p)
 #define __put_user_check __put_user_nocheck
 
 #endif /* CONFIG_MMU */
 
-#define access_ok(addr, size)	(__range_ok(addr, size) == 0)
+#include <asm-generic/access_ok.h>
 
 #ifdef CONFIG_CPU_SPECTRE
 /*