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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: From d340fac886c4a15d39d8e963aa8c647b19589413 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 29 Oct 2024 22:03:31 +0100 Subject: [PATCH] x86/mm/pat: (un)track_pfn_copy() fix + improvements We got a late smatch warning and some additional review feedback. smatch warnings: mm/memory.c:1428 copy_page_range() error: uninitialized symbol 'pfn'. We actually use the pfn only when it is properly initialized; however, we may pass an uninitialized value to a function -- although it will not use it that likely still is UB in C. Fix it by always initializing pfn when track_pfn_copy() returns 0 -- just as documented. While at it, clarify the doc of untrack_pfn_copy(), that internal checks make sure if we actually have to untrack anything. Fixes: dc84bc2aba85 ("x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()") Reported-by: kernel test robot Reported-by: Dan Carpenter Closes: https://lore.kernel.org/r/202503270941.IFILyNCX-lkp@intel.com/ Cc: Andrew Morton Cc: Lorenzo Stoakes Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Rik van Riel Cc: "H. Peter Anvin" Cc: Linus Torvalds Cc: Andrew Morton Signed-off-by: David Hildenbrand --- arch/x86/mm/pat/memtype.c | 4 +++- include/linux/pgtable.h | 5 ++++- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index 72d8cbc611583..9ad3e5b055d8a 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -992,8 +992,10 @@ int track_pfn_copy(struct vm_area_struct *dst_vma, pgprot_t pgprot; int rc; - if (!(src_vma->vm_flags & VM_PAT)) + if (!(src_vma->vm_flags & VM_PAT)) { + *pfn = 0; return 0; + } /* * Duplicate the PAT information for the dst VMA based on the src diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index e2b705c149454..9457064292141 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -1517,12 +1517,15 @@ static inline void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot, static inline int track_pfn_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, unsigned long *pfn) { + *pfn = 0; return 0; } /* * untrack_pfn_copy is called when a VM_PFNMAP VMA failed to copy during - * copy_page_range(), but after track_pfn_copy() was already called. + * copy_page_range(), but after track_pfn_copy() was already called. Can + * be called even if track_pfn_copy() did not actually track anything: + * handled internally. */ static inline void untrack_pfn_copy(struct vm_area_struct *dst_vma, unsigned long pfn) -- 2.48.1 > > I mean the patch is already upstream at dc84bc2aba85. So I guess these fixes are > intended for rc generally? Yes. -- Cheers, David / dhildenb