From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D58843A4508; Sat, 12 Sep 2026 07:05:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789196741; cv=none; b=GwNtwpg8ORzAhgd5aRFvN7qhCyCtG2EpizGjVHkJUB3NnePTZQpCzvE66vKhG08Ou2iw8vP7KiPTMJEDbaNmEiTqnmoeU67MRl6tLvPpZrzj0G3QJY/2ORPYQbeWVYngJTKSb+Hg33OsOR9XVVoyvBVCxTAJIa8CekyUawkwpVI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789196741; c=relaxed/simple; bh=x/LSAT18OTxmXhCe16P05z++UyWC6c6vM9FZtRtNsuY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=rsFwbpkEBKbtjX35JFfDSeCtEpFuoPxzhA7fzr+WF1dChqZ5GhoRUCbbTFAbP2vfDt6gzs8KngIV7mffKljBHkDEe9AKDCW/sza+fMCEhQqHbyXK3BI/wFdZjrQQttu7Wsdp6DCD0dJrsfWbwos+HIFB3QoCJrE5fXUKKKvqZ68= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=m20hBk22; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="m20hBk22" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2DC41F000FF; Sat, 12 Sep 2026 07:05:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789196737; bh=OYx59bh5WwclGILyI20Xe8OE3ecnZCiT7X1Xw3kVJD4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=m20hBk22ZtZbaZdZbCxs+9xLMHh+0WiNqJjQYGG/0a7VTop36r+M8C6IdOIqfsq/k e7tvNRrucR7H7F7oK7nmGxx5qgBQZSTOiMovFcXBUDuCfAe7FtcZ0JUqaIG8vAPXUc vgA2dQAvI21fK8cTi5J5MBLkRiAi69q7ESA6duAg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Lorenzo Stoakes (ARM)" , syzbot+f12658786a4153df5113@syzkaller.appspotmail.com, "Vlastimil Babka (SUSE)" , Kunwu Chan , Pedro Falcato , Jann Horn , "Liam R. Howlett" , Li Xinhai , Andrew Morton , Sasha Levin Subject: [PATCH 7.2 0027/1815] mm/mremap: reset unfaulted VMA page offset for MREMAP_DONTUNMAP Date: Sat, 12 Sep 2026 08:29:37 +0200 Message-ID: <20260912065649.644976708@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065648.999753832@linuxfoundation.org> References: <20260912065648.999753832@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: "Lorenzo Stoakes (ARM)" [ Upstream commit 35b0fb391b0df57383bc15985bb769f4555c97ba ] Uniquely an mremap() invocation using the MREMAP_DONTUNMAP flag can reset a faulted VMA into an unfaulted one. It does so after the page tables have been moved to the copied VMA with MREMAP_DONTUNMAP leaving the old VMA in place which is naturally unfaulted as the page tables it had are no longer present. However, in doing so, it violates the invariant that the anonymous page offset of an unfaulted VMA is vma->vm_start >> PAGE_SHIFT. This is because a VMA may have been faulted in, mremap()'d (causing a delta between its page offset and vma->vm_start >> PAGE_SHIFT), and then mremap()'d again with MREMAP_DONTUNMAP resulting in the unfaulting. This condition is a violation of a fundamental assumption in mm, but now also triggers an assert in assert_sane_pgoff() which explicitly checks for this condition. Correct it by resetting the VMA's page offset at the point of completing the MREMAP_DONTUNMAP operation. Link: https://lore.kernel.org/20260825-fix-mremap-dontunmap-pgoff-v1-1-39a40b2c98b3@kernel.org Fixes: 1583aa278f5f ("mm: mremap: unlink anon_vmas when mremap with MREMAP_DONTUNMAP success") Signed-off-by: Lorenzo Stoakes (ARM) Reported-by: syzbot+f12658786a4153df5113@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6a87853b.ae6ddae5.3da009.0023.GAE@google.com/ Tested-by: syzbot+f12658786a4153df5113@syzkaller.appspotmail.com Acked-by: Vlastimil Babka (SUSE) Reviewed-by: Kunwu Chan Reviewed-by: Pedro Falcato Cc: Jann Horn Cc: Liam R. Howlett Cc: Li Xinhai Cc: Signed-off-by: Andrew Morton [ adapted VMA page-offset helpers to use the branch’s single vm_pgoff field. ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- mm/mremap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) --- a/mm/mremap.c +++ b/mm/mremap.c @@ -1321,18 +1321,29 @@ static void dontunmap_complete(struct vm { unsigned long start = vrm->addr; unsigned long end = vrm->addr + vrm->old_len; - unsigned long old_start = vrm->vma->vm_start; - unsigned long old_end = vrm->vma->vm_end; + struct vm_area_struct *vma = vrm->vma; + unsigned long old_start = vma->vm_start; + unsigned long old_end = vma->vm_end; /* We always clear VM_LOCKED[ONFAULT] on the old VMA. */ - vm_flags_clear(vrm->vma, VM_LOCKED_MASK); + vm_flags_clear(vma, VM_LOCKED_MASK); /* * anon_vma links of the old vma is no longer needed after its page * table has been moved. */ - if (new_vma != vrm->vma && start == old_start && end == old_end) - unlink_anon_vmas(vrm->vma); + if (new_vma != vma && start == old_start && end == old_end) { + const pgoff_t pgoff_unfaulted = vma->vm_start >> PAGE_SHIFT; + + unlink_anon_vmas(vma); + /* + * The VMA is now unfaulted and it is an invariant that + * unfaulted anonymous VMAs have page offset equal to + * vma->vm_start >> PAGE_SHIFT. + */ + if (vma_is_anonymous(vma) && !vma->vm_file) + vma->vm_pgoff = pgoff_unfaulted; + } /* Because we won't unmap we don't need to touch locked_vm. */ }