Re: [PATCH v3] x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()

[David Hildenbrand <david@redhat.com>]

On 04.04.25 14:20, David Hildenbrand wrote:
> On 04.04.25 13:52, Lorenzo Stoakes wrote:
>> On Thu, Apr 03, 2025 at 10:59:12PM +0200, David Hildenbrand wrote:
>>> On 03.04.25 17:14, Dan Carpenter wrote:
>>>> Sorry, I've been having trouble with my email recently...  I replied
>>>> earlier but my email got eaten on the way out.
>>>>
>>>> What happened here is that the zero day bot emails go to me first and
>>>> then I review them or forward them depending on if they're a real
>>>> issue or not.
>>>>
>>>> Here it's a false postive because it's set and used if the
>>>> (src_vma->vm_flags & VM_PFNMAP) flag is set.  Smatch doesn't parse
>>>> this correctly.  I've been meaning to fix this in Smatch for a
>>>> while.
>>>
>>> There is a slight complication (on top of the VM_PFNMAP checks):
>>>
>>> If "src_vma->vm_flags & VM_PAT" we
>>> * set pfn
>>> * set dst_vma->vm_flags |= VM_PFNMAP
>>>
>>> Then, we only consume the pfn if "dst_vma->vm_flags & VM_PFNMAP"
>>>
>>> While we won't be using the uninitialized pfn (good), we'd still pass an
>>> uninitialized pfn, which IIRC is UB; likely nothing happens on GCC clang,
>>> but we better handle it.
>>>
>>> So that should better be changed; I'll send a fix.
>>
>> Maybe just worth setting pfn = 0 _as well_ in the caller, belts + braces maybe?
> 
> I'm planning on doing the following, just didn't get to testing it:
> 

Ah, now I get your comment. Yeah, we could just set pfn=0 in the caller 
as well to make smatch completely happy I guess.

-- 
Cheers,

David / dhildenb