# Pastebin 7339iWaA
commit 4f9cb5d7696f61d66d3476b616f4220a4cdf5c04
Author: Arnd Bergmann <arnd@arndb.de>
Date:   Mon Feb 14 09:00:10 2022 +0100

    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.
    
    Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index db16bc9ee187..7b4b0421ce28 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -28,6 +28,9 @@
 
 #define HAVE_GET_KERNEL_NOFAULT
 
+
+static inline int __access_ok(const void __user *ptr, unsigned long size);
+
 /*
  * Test whether a block of memory is a valid user space address.
  * Returns 1 if the range is valid, 0 otherwise.
@@ -35,10 +38,8 @@
  * This is equivalent to the following test:
  * (u65)addr + (u65)size <= (u65)TASK_SIZE_MAX
  */
-static inline unsigned long __access_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
@@ -48,27 +49,9 @@ static inline unsigned long __access_ok(const void __user *addr, unsigned long s
 	    (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 __access_ok
+#define access_ok access_ok
 
 #include <asm-generic/access_ok.h>