linux-kernel - Re: [PATCH v1] mm/gup: remove (VM_)BUG

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

Message-ID: <23316621-0338-476f-b255-9ac4dff15d8b@redhat.com>
Date: Wed, 4 Jun 2025 21:16:16 +0200
From: David Hildenbrand <david@...hat.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Jason Gunthorpe <jgg@...pe.ca>, John Hubbard <jhubbard@...dia.com>,
 Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs

On 04.06.25 21:12, Liam R. Howlett wrote:
> * David Hildenbrand <david@...hat.com> [250604 10:06]:
>> Especially once we hit one of the assertions in
>> sanity_check_pinned_pages(), observing follow-up assertions failing
>> in other code can give good clues about what went wrong, so use
>> VM_WARN_ON_ONCE instead.
>>
>> While at it, let's just convert all VM_BUG_ON to VM_WARN_ON_ONCE as
>> well. Add one comment for the pfn_valid() check.
>>
>> We have to introduce VM_WARN_ON_ONCE_VMA() to make that fly.
>>
>> Drop the BUG_ON after mmap_read_lock_killable(), if that ever returns
>> something > 0 we're in bigger trouble. Convert the other BUG_ON's into
>> VM_WARN_ON_ONCE as well, they are in a similar domain "should never
>> happen", but more reasonable to check for during early testing.
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>> Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Mike Rapoport <rppt@...nel.org>
>> Cc: Suren Baghdasaryan <surenb@...gle.com>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Jason Gunthorpe <jgg@...pe.ca>
>> Cc: John Hubbard <jhubbard@...dia.com>
>> Cc: Peter Xu <peterx@...hat.com>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
> 
> seems okay, besides the one nit.
> 
> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

[...]

>>   
>>   	ret = handle_mm_fault(vma, address, fault_flags, NULL);
>> @@ -1760,10 +1760,7 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
>>   		}
>>   
>>   		/* VM_FAULT_RETRY or VM_FAULT_COMPLETED cannot return errors */
>> -		if (!*locked) {
>> -			BUG_ON(ret < 0);
>> -			BUG_ON(ret >= nr_pages);
>> -		}
>> +		VM_WARN_ON_ONCE(!*locked && (ret < 0 || ret >= nr_pages));
> 
> nit, we are losing accuracy on the value of ret here.  I doubt it makes
> much of a difference though.

Yeah I doubt this will matter.

Thanks!

-- 
Cheers,

David / dhildenb