Sparse has identified a warning as follows:

./arch/x86/include/asm/uaccess_64.h:88:24: warning: cast removes address space '__user' of expression.

Since the valid_user_address(x) macro implicitly casts the argument
to long and compares the converted value of x to zero, casting ptr
to unsigned long has no functional impact and does not trigger a 
Sparse warning either.

Signed-off-by: Dipendra Khadka <kdipendra88@gmail.com>
---
 arch/x86/include/asm/uaccess_64.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index f2c02e4469cc..da24d807e101 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -85,7 +85,7 @@ static inline unsigned long __untagged_addr_remote(struct mm_struct *mm,
 static inline bool __access_ok(const void __user *ptr, unsigned long size)
 {
 	if (__builtin_constant_p(size <= PAGE_SIZE) && size <= PAGE_SIZE) {
-		return valid_user_address(ptr);
+		return valid_user_address((unsigned long)ptr);
 	} else {
 		unsigned long sum = size + (unsigned long)ptr;
 		return valid_user_address(sum) && sum >= (unsigned long)ptr;
-- 
2.34.1

On 11/16/23 09:38, Dipendra Khadka wrote:
> Sparse has identified a warning as follows:
> 
> ./arch/x86/include/asm/uaccess_64.h:88:24: warning: cast removes address space '__user' of expression.
> 
> Since the valid_user_address(x) macro implicitly casts the argument
> to long and compares the converted value of x to zero, casting ptr
> to unsigned long has no functional impact and does not trigger a 
> Sparse warning either.

Why does sparse complain about a cast to 'long' but not 'unsigned long'?
 Both remove the '__user' address space from the expression.  Were there
just so many __user pointers being cast to 'unsigned long' that there's
an exception in sparse for 'void __user *' => 'unsigned long'?

Either way, if we're going to fix it it seems like it would be better to
valid_user_address() actually handle, well, __user addresses rather than
expecting callers to do it.

On Fri, Nov 17, 2023 at 07:19:12AM -0800, Dave Hansen wrote:
> On 11/16/23 09:38, Dipendra Khadka wrote:
> > Sparse has identified a warning as follows:
> > 
> > ./arch/x86/include/asm/uaccess_64.h:88:24: warning: cast removes address space '__user' of expression.
> > 
> > Since the valid_user_address(x) macro implicitly casts the argument
> > to long and compares the converted value of x to zero, casting ptr
> > to unsigned long has no functional impact and does not trigger a 
> > Sparse warning either.
> 
> Why does sparse complain about a cast to 'long' but not 'unsigned long'?
>  Both remove the '__user' address space from the expression.  Were there
> just so many __user pointers being cast to 'unsigned long' that there's
> an exception in sparse for 'void __user *' => 'unsigned long'?

Yes, unsigned long is special:

commit 7816e4c4a2dba6fef24c9a52c6b17a8cde0c8138
Author: Linus Torvalds <torvalds@ppc970.osdl.org>
Date:   Mon May 31 13:18:57 2004 -0700

    Allow casting of user pointers to "unsigned long".

    It's reasonably common to do special pointer arithmetic
    in unsigned long, and making people force the cast just
    adds noise.


I wonder if we should have:

#define valid_user_address(x) ((__force long)(x) >= 0)

or  

#define valid_user_address(x) ((long)(unsigned long)(x) >= 0)

Thanks.

-- 
Dmitry