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Howlett" , x86@kernel.org Subject: Re: [PATCH v3] x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range() Message-ID: <202ba609-277d-4f16-92df-8a5a94f99ad4@stanley.mountain> References: <94c35e89-f915-4122-b1a0-436893201373@stanley.mountain> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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. Passing an uninitialized variable is UB, but if the function is inlined then it's fine. regards, dan carpenter