From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792763282; b=nZP2RQjZyVRDiGb0mm3r8yaSjm016V8VGF8YM+7dKd45494NdgP47ENl+bqRmJqtBXw4 WiBKJzkhU/81QvQ9IqyLnmXN+kcLO8YWcS7j+baHHLLQBOxc3EXwsYl3xC0foGSDE0p2a 5fK5LHweuW0sLBL6bVNgb8EfQsZFejk42MTMmM0ffR2jL2GY5EAzm0Anz4mClp/Tpckjs zP/U4CXU6ai1ZJTcNuNPLU4r+AL3GLH6+op6zsHsz3GUSrxPSZKCZQdbLcKqyY1jMwNq7 MMjxI5jL3HM708+L3JBA5bu1gar++cyjhCblrRz+AEjMv7r3YiCc3u4+4pE1yjdOLxw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792763282; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=DjY0J1rY8s6eI0pi00146/qxLG5XIFRaa8H6rSeRSdI=; b=pOiq2YJ8ESB/dC3jVMw8gLPnAJMUFZellSxVPEhTipF/eitiEhFCGpj0Hqb2XKfR63pd uq494Tc1IuwabK3D2K44Yj3oq3VzL1tFNgaB6/X32LJwPxIzQ/Ou2UDq0lgDEFRA1tlKR tVtSgSGWxYVa78Pls+Fb6ICVFW+KJtl74LRSIC+8YrQSpdenyrW3QT0MlsjvsxU/bULAk jg7OFL1f3oByhcCFXmDFg/RnUDwMHZZES696sgrkcU1S/fF/J8uSjHttQeCGhSlwsTNL+ ZhWO87vbdzqKBeGUJz6MyhkOB4bs5zd9WenaxgEGQ4MwFyVw0I7KKAPNrkF40DyOa1g== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=dfqKVI6g; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 20733606A32C; Fri, 23 Oct 2026 13:48:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=dfqKVI6g Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06E311F031E1; Fri, 23 Oct 2026 13:47:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792763281; bh=DjY0J1rY8s6eI0pi00146/qxLG5XIFRaa8H6rSeRSdI=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=dfqKVI6giPzt5zbodp+Y1rpDLUD/m3efycWZdeUMPGiIL7r5+EnNhAsnZJ5ftfgo7 Cien+WUpFTsX+Uvqev3Z7aqzdnx1iXRYPHn5ZfYwDzI1SY0IBLtpUV1LGL20y7e+fp 7vtGVZh5y+n9V4m6Vfy2RbW/ErwbMmvcFmOCEQa8ItSKJBZREYjLj9Be23Oq67oaJx NH/Y4GI346SxjhQckJ18s/BSiXQVHtFP/TXTtZp1HiIgNcoHz4e2L+0AJHiFBAIAob F9QyxgcB91Bw7/EQ3JJ6GD9ijywRpjS+93OHzjDqXBw4AgE7d6Y7JcY8iEJxP66SaP LaSiL8GJz7WLw== From: "Lorenzo Stoakes (ARM)" Date: Fri, 23 Oct 2026 14:47:28 +0100 Subject: [PATCH 2/4] mm/vma: write lock source VMA before duplicating it in __split_vma() X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261023-fix-vma-atomic-v1-2-8ff4fae1fc85@kernel.org> References: <20261023-fix-vma-atomic-v1-0-8ff4fae1fc85@kernel.org> In-Reply-To: <20261023-fix-vma-atomic-v1-0-8ff4fae1fc85@kernel.org> To: Andrew Morton , David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , Davidlohr Bueso , SJ Park , Kees Cook , Colin Cross Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Lorenzo Stoakes (ARM)" , stable@vger.kernel.org X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=2019; i=ljs@kernel.org; h=from:subject:message-id; bh=pBDKonRJs5TA7YWHg4RHbXCo1gcPUiIEkJW4rM9Bgss=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLJup7ZwnTcrklmpLv+v7b5ZTk5rgu3W38Kusn8WXX+/P +DA96yYjlIWBjEuBlkxRZbnX8T3B4mEzeu84O8GM4eVCWQIAxenAEzk52GGvwI27BPt4hz1fVt+ GIvef1ex+25XdOuMn8UV36YvjTrWIM7I8NIhpL7vNP/EEvbTHnKC/83mnWg2v2t7j23qWYOY0zu XcAAA X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 From: "David Hildenbrand (Arm)" __split_vma() duplicates the source VMA before taking its VMA write lock, and until the VMA is write-locked, a concurrent thread might set VMA_MAYBE_GUARD_BIT, resulting in the duplication missing the flag. If this happens, then fork may fail to duplicate guard markers and, if a file-backed mapping, THP collapse may also discard the markers. Resolve this by taking the VMA write lock before vm_area_dup() and, since all callers of vm_area_dup() now hold the VMA write lock, assert that this is the case there, and add a comment to explain why it's needed. Fixes: 2ab7f1bbafc9 ("mm/madvise: allow guard page install/remove under VMA lock") Cc: Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Lorenzo Stoakes (ARM) [ ljs - add VMA write assert in vm_area_dup(), commit message touchup ] Signed-off-by: Lorenzo Stoakes (ARM) --- mm/vma.c | 2 +- mm/vma_init.c | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/vma.c b/mm/vma.c index 1be613044b4a..aa59005e2f42 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -538,6 +538,7 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, return err; } + vma_start_write(vma); new = vm_area_dup(vma); if (!new) return -ENOMEM; @@ -568,7 +569,6 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, if (new->vm_ops && new->vm_ops->open) new->vm_ops->open(new); - vma_start_write(vma); vma_start_write(new); init_vma_prep(&vp, vma); diff --git a/mm/vma_init.c b/mm/vma_init.c index baa7e82f47e3..d661f229a734 100644 --- a/mm/vma_init.c +++ b/mm/vma_init.c @@ -127,6 +127,9 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig) { struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL); + /* Must hold a write lock to stabilise atomic VMA flags. */ + vma_assert_write_locked(orig); + if (!new) return NULL; -- 2.56.0