[PATCH 1/2] arm64: uaccess: Clean up types for access_ok()

[Robin Murphy]

In converting __range_ok() into a static inline, I inadvertently made
it more type-safe, but without considering the ordering of the relevant
conversions. This leads to quite a lot of Sparse noise about the fact
that we use __chk_user_ptr() after addr has already been converted from
a user pointer to an unsigned long.

Tweak the prototype and locals so the types all make logical sense and
Sparse is happy (although the resulting codegen remains identical). The
only external site this affects is in compat syscalls where the inferred
"user-pointer-ness" of a register value now warrants an explicit cast.

Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---
 arch/arm64/include/asm/uaccess.h | 12 ++++++------
 arch/arm64/kernel/sys_compat.c   |  2 +-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 543e11f0f657..e66b0fca99c2 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -72,15 +72,15 @@ static inline void set_fs(mm_segment_t fs)
  * This is equivalent to the following test:
  * (u65)addr + (u65)size <= (u65)current->addr_limit + 1
  */
-static inline unsigned long __range_ok(unsigned long addr, unsigned long size)
+static inline unsigned long __range_ok(const void __user *addr, unsigned long size)
 {
-	unsigned long limit = current_thread_info()->addr_limit;
+	unsigned long ret, limit = current_thread_info()->addr_limit;
 
 	__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, %0, %2\n"
+	"	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'
@@ -92,9 +92,9 @@ static inline unsigned long __range_ok(unsigned long addr, unsigned long size)
 	//    testing X' - C == 0, subject to the previous adjustments.
 	"	sbcs	xzr, %0, %1\n"
 	"	cset	%0, ls\n"
-	: "+r" (addr), "+r" (limit) : "Ir" (size) : "cc");
+	: "=&r" (ret), "+r" (limit) : "Ir" (size), "0" (addr) : "cc");
 
-	return addr;
+	return ret;
 }
 
 /*
@@ -104,7 +104,7 @@ static inline unsigned long __range_ok(unsigned long addr, unsigned long size)
  */
 #define untagged_addr(addr)		sign_extend64(addr, 55)
 
-#define access_ok(type, addr, size)	__range_ok((unsigned long)(addr), size)
+#define access_ok(type, addr, size)	__range_ok(addr, size)
 #define user_addr_max			get_fs
 
 #define _ASM_EXTABLE(from, to)						\
diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c
index 8b8bbd3eaa52..a382b2a1b84e 100644
--- a/arch/arm64/kernel/sys_compat.c
+++ b/arch/arm64/kernel/sys_compat.c
@@ -57,7 +57,7 @@ do_compat_cache_op(unsigned long start, unsigned long end, int flags)
 	if (end < start || flags)
 		return -EINVAL;
 
-	if (!access_ok(VERIFY_READ, start, end - start))
+	if (!access_ok(VERIFY_READ, (const void __user *)start, end - start))
 		return -EFAULT;
 
 	return __do_compat_cache_op(start, end);
-- 
2.16.1.dirty