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 E7A57388390 for ; Fri, 11 Sep 2026 09:42:02 +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=1789119724; cv=none; b=mxsDC/cWimp1YaZGlv9q7P7HG6sxsAapkMs0StYSfeFq0XPqHvU0c04Mz8brlpWprqPUfhE8Kz8VWT7lq8PodeIS3socaWRt0s1zK+BZ66W037HG4ACJn91F21T0Us4YCzUyjk/ixBggRKe7WV0ZqdnL0Mdn1S5vE/Fk37u1o+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789119724; c=relaxed/simple; bh=o1y/z7Ku1dnGsg/17HxtmbCVjwmdCErA7P+qsmdg0TY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TeCQfAW+h3cUGNLp4nz4SUgDqy+hooLsSGYnzgBqESVVYNs5bi1eSNw8mPbLR03jrh5lYzam/67RlQ1dziMnMAIpjOxpIMfqY55+Pbi7ZLeScApEZ6mERKh3ze2U3DVqCrY/JVuAVJ9X0lTx/7crSUPoh+ZZV4X2KXY2ZNA6ruE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IP9YRKLn; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IP9YRKLn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 812691F000FF; Fri, 11 Sep 2026 09:41:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789119722; bh=0yZtW6BeJcEiWxOumhdHsf42XF2Wb8UaCY0cfQFl3wM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=IP9YRKLnvrdKRc+IrCzaW61+fEZ12Dter+rQSq953lFRPf26q7bxZKrgXPe08/YvA S9RbWkrckCFETNn3/l4iFryi5fca1lxIw6F7pIEGrAL01GbUVtjqeETrL5eW47hWRc cmeuklxV+CTO1qmkdubGt2bBf3hs1aumldaUdPhfXwFI+MQhob/ZJBJ/9B4YJfA2nI 1NgCoxK8P19/SekcGUpNjV06dSGJmGSbbHmaMKcgRVlc4ILOZyFPS+Wix4btkgUaMP Ms4w9pAmz+Odu/ls+vQOaJ49mrgdnTRkpNiXHEFLrUpg11ISYNsRjskBvNWcnv4l6G 1kc8VG5Fnbzjw== Date: Fri, 11 Sep 2026 10:41:56 +0100 From: "Lorenzo Stoakes (ARM)" To: Sasha Levin Cc: stable@vger.kernel.org, syzbot+f12658786a4153df5113@syzkaller.appspotmail.com, "Vlastimil Babka (SUSE)" , Kunwu Chan , Pedro Falcato , Jann Horn , "Liam R. Howlett" , Li Xinhai , Andrew Morton Subject: Re: [PATCH 6.12.y] mm/mremap: reset unfaulted VMA page offset for MREMAP_DONTUNMAP Message-ID: References: <2026090957-prideful-repulsive-38a0@gregkh> <20260911021410.42929-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@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: <20260911021410.42929-1-sashal@kernel.org> On Thu, Sep 10, 2026 at 10:14:10PM -0400, Sasha Levin wrote: > 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 dontunmap_complete() changes to move_vma() using direct vm_pgoff assignment instead of unavailable helpers. ] > Signed-off-by: Sasha Levin LGTM thanks! > --- > mm/mremap.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/mm/mremap.c b/mm/mremap.c > index 12af89b4342a7..9685ea816fde1 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -811,8 +811,18 @@ static unsigned long move_vma(struct vm_area_struct *vma, > * table has been moved. > */ > if (new_vma != vma && vma->vm_start == old_addr && > - vma->vm_end == (old_addr + old_len)) > + vma->vm_end == (old_addr + old_len)) { > + 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 */ > return new_addr; > -- > 2.53.0 > -- Cheers, Lorenzo