linux-kernel - Re: [PATCH] mm/selftests: Fix -Wtautological-compare warning in mremap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <20251110100914.af77cb0a5b4211313dd9f32a@linux-foundation.org>
Date: Mon, 10 Nov 2025 10:09:14 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Wake Liu <wakel@...gle.com>
Cc: David Hildenbrand <david@...hat.com>, Shuah Khan <shuah@...nel.org>,
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan
 <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Ankit Khushwaha
 <ankitkhushwaha.linux@...il.com>
Subject: Re: [PATCH] mm/selftests: Fix -Wtautological-compare warning in
 mremap_test.c

On Tue, 11 Nov 2025 01:51:55 +0800 Wake Liu <wakel@...gle.com> wrote:

> The compiler warns about a tautological comparison in mremap_test.c:
> "pointer comparison always evaluates to false [-Wtautological-compare]"
> 
> This occurs when checking for unsigned overflow:
>   if (addr + c.dest_alignment < addr)
> 
> Cast 'addr' to 'unsigned long long' to ensure the comparison is performed
> with a wider type, correctly detecting potential overflow and resolving
> the warning.
> 

Thanks.  I recently merged

https://lore.kernel.org/all/20251108161829.25105-1-ankitkhushwaha.linux@gmail.com/T/#u

there has been some discussion...

> --- a/tools/testing/selftests/mm/mremap_test.c
> +++ b/tools/testing/selftests/mm/mremap_test.c
> @@ -1032,7 +1032,7 @@ static long long remap_region(struct config c, unsigned int threshold_mb,
>  	/* Don't destroy existing mappings unless expected to overlap */
>  	while (!is_remap_region_valid(addr, c.region_size) && !c.overlapping) {
>  		/* Check for unsigned overflow */
> -		if (addr + c.dest_alignment < addr) {
> +		if ((unsigned long long)addr + c.dest_alignment < (unsigned long long)addr) {
>  			ksft_print_msg("Couldn't find a valid region to remap to\n");
>  			ret = -1;
>  			goto clean_up_src;

I wonder if we'd be better off borrowing ideas from
include/linux/overflow.h:check_add_overflow().  Did anyone try
__builtin_add_overflow() here?