Commit 52fe8d12 authored by Arnd Bergmann's avatar Arnd Bergmann
Browse files

arm64: simplify access_ok() 



arm64 has an inline asm implementation of access_ok() that is derived from
the 32-bit arm version and optimized for the case that both the limit and
the size are variable. With set_fs() gone, the limit is always constant,
and the size usually is as well, so just using the default implementation
reduces the check into a comparison against a constant that can be
scheduled by the compiler.

On a defconfig build, this saves over 28KB of .text.

Acked-by: default avatarRobin Murphy <robin.murphy@arm.com>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
parent 26509034

arch/arm64/include/asm/uaccess.h

+10 −24
Original line number Diff line number Diff line
@@ -26,6 +26,14 @@ 
#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));

}



/*

 * Test whether a block of memory is a valid user space address.

 * Returns 1 if the range is valid, 0 otherwise.
@@ -33,10 +41,8 @@ 
 * This is equivalent to the following test:

 * (u65)addr + (u65)size <= (u65)TASK_SIZE_MAX

 */

static inline unsigned long __range_ok(const void __user *addr, unsigned long size)

static inline int access_ok(const void __user *addr, unsigned long size)

{

	unsigned long ret, limit = TASK_SIZE_MAX - 1;



	/*

	 * Asynchronous I/O running in a kernel thread does not have the

	 * TIF_TAGGED_ADDR flag of the process owning the mm, so always untag
@@ -46,29 +52,9 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si 
	    (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR)))

		addr = untagged_addr(addr);



	__chk_user_ptr(addr);

	asm volatile(

	// A + B <= C + 1 for all A,B,C, in four easy steps:

	// 1: X = A + B; X' = X % 2^64

	"	adds	%0, %3, %2\n"

	// 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4

	"	csel	%1, xzr, %1, hi\n"

	// 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'

	//    to compensate for the carry flag being set in step 4. For

	//    X > 2^64, X' merely has to remain nonzero, which it does.

	"	csinv	%0, %0, xzr, cc\n"

	// 4: For X < 2^64, this gives us X' - C - 1 <= 0, where the -1

	//    comes from the carry in being clear. Otherwise, we are

	//    testing X' - C == 0, subject to the previous adjustments.

	"	sbcs	xzr, %0, %1\n"

	"	cset	%0, ls\n"

	: "=&r" (ret), "+r" (limit) : "Ir" (size), "0" (addr) : "cc");



	return ret;

	return likely(__access_ok(addr, size));

}



#define access_ok(addr, size)	__range_ok(addr, size)



/*

 * User access enabling/disabling.

 */