From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7F6FA33B6ED; Fri, 9 Jan 2026 12:53:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767963206; cv=none; b=BaYiNKemSBm3qcyK2aPHI328qMjpCAjmlhfkIiegLQCqSX9yByleA+UKCXAFsY6c62vYZjguzGLjVJCIeehC2ef+vAhyu8CzFyR4P1QpwiGxH0agQTusWGqW1hDgtSrUKHEyAxNsXknwQp2TrOJgAvPSBTtCsMVlpfrCQpLwWtQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767963206; c=relaxed/simple; bh=J0/wiaTbEJI2t1mOA0TNqfEeBN2ayLMAiRJOTZJVO0U=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GjR0GxvU0WlKU9v8iHtw6eo7a6nAPy8o1QBpwCo0jKt2XSDBZbf8VB13NF4tasQO2VIfFRDK7cRZTf68dyTTHfUygRhrcCVwVdhRjy4w2xDIaCh/XLbIGoAqPwhYLN59xWzEcQSiJ+NDlH2cCbW0pGPVtXGAVTQnytXFw3VdMDY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=FXi7klyJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="FXi7klyJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9A86C4CEF1; Fri, 9 Jan 2026 12:53:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767963206; bh=J0/wiaTbEJI2t1mOA0TNqfEeBN2ayLMAiRJOTZJVO0U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FXi7klyJGFCpMfGlSkhybg8PNwPNB2/P3da6qVzMlK8H2JW7u1j7mU2b+cyCgKC5V svgbkWgyKMvhi7FmDkrAxWqJFrLx/JxqcqTBEb4OPdU0N3gqLYpJk2Ibuf95Odqh/c NjlOSfBi8Hd9dk+DxRaY+e68sYM2XXtK/XMSEpKI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, David Hildenbrand , Lorenzo Stoakes , Ingo Molnar , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Borislav Petkov , Rik van Riel , "H. Peter Anvin" , Linus Torvalds , Andrew Morton Subject: [PATCH 6.1 627/634] kernel/fork: only call untrack_pfn_clear() on VMAs duplicated for fork() Date: Fri, 9 Jan 2026 12:45:05 +0100 Message-ID: <20260109112141.229726861@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260109112117.407257400@linuxfoundation.org> References: <20260109112117.407257400@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Hildenbrand commit e9f180d7cfde23b9f8eebd60272465176373ab2c upstream. Not intuitive, but vm_area_dup() located in kernel/fork.c is not only used for duplicating VMAs during fork(), but also for duplicating VMAs when splitting VMAs or when mremap()'ing them. VM_PFNMAP mappings can at least get ordinarily mremap()'ed (no change in size) and apparently also shrunk during mremap(), which implies duplicating the VMA in __split_vma() first. In case of ordinary mremap() (no change in size), we first duplicate the VMA in copy_vma_and_data()->copy_vma() to then call untrack_pfn_clear() on the old VMA: we effectively move the VM_PAT reservation. So the untrack_pfn_clear() call on the new VMA duplicating is wrong in that context. Splitting of VMAs seems problematic, because we don't duplicate/adjust the reservation when splitting the VMA. Instead, in memtype_erase() -- called during zapping/munmap -- we shrink a reservation in case only the end address matches: Assume we split a VMA into A and B, both would share a reservation until B is unmapped. So when unmapping B, the reservation would be updated to cover only A. When unmapping A, we would properly remove the now-shrunk reservation. That scenario describes the mremap() shrinking (old_size > new_size), where we split + unmap B, and the untrack_pfn_clear() on the new VMA when is wrong. What if we manage to split a VM_PFNMAP VMA into A and B and unmap A first? It would be broken because we would never free the reservation. Likely, there are ways to trigger such a VMA split outside of mremap(). Affecting other VMA duplication was not intended, vm_area_dup() being used outside of kernel/fork.c was an oversight. So let's fix that for; how to handle VMA splits better should be investigated separately. With a simple reproducer that uses mprotect() to split such a VMA I can trigger x86/PAT: pat_mremap:26448 freeing invalid memtype [mem 0x00000000-0x00000fff] Link: https://lkml.kernel.org/r/20250422144942.2871395-1-david@redhat.com Fixes: dc84bc2aba85 ("x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()") Signed-off-by: David Hildenbrand Reviewed-by: Lorenzo Stoakes Cc: Ingo Molnar Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Rik van Riel Cc: "H. Peter Anvin" Cc: Linus Torvalds Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- kernel/fork.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/kernel/fork.c +++ b/kernel/fork.c @@ -476,10 +476,6 @@ struct vm_area_struct *vm_area_dup(struc *new = data_race(*orig); INIT_LIST_HEAD(&new->anon_vma_chain); dup_anon_vma_name(orig, new); - - /* track_pfn_copy() will later take care of copying internal state. */ - if (unlikely(new->vm_flags & VM_PFNMAP)) - untrack_pfn_clear(new); } return new; } @@ -650,6 +646,11 @@ static __latent_entropy int dup_mmap(str tmp = vm_area_dup(mpnt); if (!tmp) goto fail_nomem; + + /* track_pfn_copy() will later take care of copying internal state. */ + if (unlikely(tmp->vm_flags & VM_PFNMAP)) + untrack_pfn_clear(tmp); + retval = vma_dup_policy(mpnt, tmp); if (retval) goto fail_nomem_policy;