From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B3859C43458 for ; Sun, 12 Jul 2026 10:47:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A47EF6B009B; Sun, 12 Jul 2026 06:47:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A1EF66B009E; Sun, 12 Jul 2026 06:47:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 95F436B009F; Sun, 12 Jul 2026 06:47:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 76C166B009B for ; Sun, 12 Jul 2026 06:47:57 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 0B32D1C9350 for ; Sun, 12 Jul 2026 10:47:57 +0000 (UTC) X-FDA: 84979799394.12.A8646BD Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf01.hostedemail.com (Postfix) with ESMTP id 6394540008 for ; Sun, 12 Jul 2026 10:47:55 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=V1ozN2CI; spf=pass (imf01.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783853275; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=/qQuNHwfggsZrnd+KuV0gCXU2w7baMsOVUJIH5eNkXk=; b=1D+YubQfCUJfWMP4NLdYGfKuaZWYtOkjRNIw1JQzhx4BN7PddII6+APM/IFRyophDwfLYr Q7cj34SfZzv7qmXHNJ43qOn9mhizQHN+9a/f+EVgOguIEoH0+ofz0Oguxyt49JdPUbH5XE TklFfPHdD5CxPek4Hkui1KVZ/st/iPE= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=V1ozN2CI; spf=pass (imf01.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783853275; b=0PObOYWj0TSnm88zN03dLukcnZxN5aIG4kfPKIBZsky8wtP+MNhEqJprsbSgGEtltXBnef RGmGXNfuiYAh4LvoQv4Mz/UEN9HYKfVhCCKEYNMkt9vDSIHV04BnZ16xw8DHuc1sS3TzuJ ucEZ51XSdziHf1trl/7Bjbv8IeUpGkk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 847E840B83; Sun, 12 Jul 2026 10:47:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5AA251F000E9; Sun, 12 Jul 2026 10:47:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783853274; bh=/qQuNHwfggsZrnd+KuV0gCXU2w7baMsOVUJIH5eNkXk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=V1ozN2CI66ESnpPd6ytBXeC3H6HMQRK81sUTWsm21lJyTwKGzX/HRRlnuAqyYbD0X IiTOsAg97PRsAt6Oq1sufKt9qpvuqnhabuDX+fqYj3UR8UzW+X3ycE9Fe5YOuBJdde XLo3/VPmEaanQVvrThzd+K8cf0ztSHDWmJWSr+JY38UvmY4KK7A2jKmlgiiD0+q0d7 W0RhK/rAJgRcPqJp6wI4Vba4z+2ph9ZZiuTzt6egY+Q5ayfqw9sunhIJO0+5AOCpn5 GzbAjhhzR4rN4YdjyS/fjZWQKLQH2puxrILzkYdDT3R2mrVoJLl1AMtLj80STq2UfQ FqAJyroPITEtQ== Date: Sun, 12 Jul 2026 11:47:40 +0100 From: Lorenzo Stoakes To: Andrew Morton Cc: David Hildenbrand , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Toshi Kani , Catalin Marinas , David Carlier , Dev Jain , Ryan Roberts , Shakeel Butt , Will Deacon , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Dave Hansen Subject: Re: [PATCH] mm/ptdump: always stabilise against page table freeing using init_mm Message-ID: References: <20260710-b4-fix-non-init_mm-ptdump-v1-1-2d40982c98ec@kernel.org> <20260710132954.49c85be140500c59c1fcb773@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6394540008 X-Stat-Signature: u4f6dnj4zcgo166xkgu8ibxac5emyjij X-HE-Tag: 1783853275-181002 X-HE-Meta: U2FsdGVkX1/SJCv0CVsWnftk8dEByWX+uc4Igp9bET68iCtVfyBkJ944IDOgqB652sC6NmdQ+ukN4EJIkTAxLfS/iwqoxgbbwoRXDwbtE+dpEXFW3HpeMbO6U+AFaGkxJ0LsitjtC1ehlyrffMFbcNP9jC5Y3Q1Thy9Kg+2LBsFWKr0VWoCcJHMNBviWtnRrviXqqI7QR1W0iLpHxfINAB13s3zTANgo6XGpmtxE+ODxRX71FjrX43v6IPBxwZHU45JdtkrGjvhehx7Jl65ScaDHU1SBhdq/xgBDNduGH1H8+gYIq4Qw5YwZ5S4t+ch6mmiYhseWaZtdV9CXtXaJP/g7t21tmFA4R+3IcGQ2Ba22eD0VKkthjmeVSQTATvvAssejflJMc0zUS1XRJAo4EtEcenGo+vXE0jFwvCrJO+SnImxyl1v5SG73IdQCCLiLr8ZZHlhujL2VvTcNA+xohEXczOaritI6MSHT4csBzomTj3U2MXdyfPUcUS/Truww48er0UNEGp0GQtHuaPeI/HE7/FxjBuxf3BBPisluw3FYZYHnFIj1k8v9p2MNf1/cyOuEkFQ+4ne7DvS+ZSBz535DkpnLA5lyx3mE1xM3aYbbThULIxViYSS9329/xY+w9gxEe5KpuCcdAZA/yqx3LQb+BozsiqJ6oX8MrpOm/Gd+b+dKj0rjj+hQDpBK6CZCkTHWra1SmknyswtUrmtlvIDcIqDWWueQb+g3d1lh/BIoaNRDjnIlbvQlph72h6/xJQW+8BFKXkoabcv3NbiiLOuvd4L/2y8tnkw5Bec0BV/kHd9yCIm5nkzDch3LAI/hvKDVEnVyzMIhgIaGHjOdLW1GMHXIUpvjX5OWUdx87xN0F/VoUYTXlOzJKLOEtvobmmv9Bj6Rhlf6LwlLlHhhXW1ZjQ1yWMTdE8+2VLwpuYViBvr5sjI0akNFKL9w5Obv91bfqkVmbadQs2hWyZO XdPsJQAL S/+FhjD8GyRF/8evB6YHao0fGOrjDuPOwoDfJHlWk2dVKMqkTKD+hX7haBYaR6O7U5+Rom8+qGALTxjrLNMSKbY6Abqg5cyjMjC6trZscB5mY0YF1WdCuM88BoISDFDi1lOTk9qCOZQYmAAe3MzLPsuCoouq3SZl3fBch25tYEUxnRy17/vVmWFr9Hg6LU+JeJER/on+ttrJDcrVjK9n4ZHLtp46a/PmdDof4er/a5cPsaKi5ig7UdWnINaYrZRAXEEIS/LETfgNfusI4EnhQITML/tqjEtdx9SFV63JvmY/Xj/P/0oc9zLD/w2g2Xu44gcUr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jul 11, 2026 at 08:57:18AM +0100, Lorenzo Stoakes wrote: > (+cc Dave as we were discussing on another thread) > > On Fri, Jul 10, 2026 at 01:29:54PM -0700, Andrew Morton wrote: > > On Fri, 10 Jul 2026 14:29:21 +0100 Lorenzo Stoakes wrote: > > > > > x86 and arm64 invokes ptdump_walk_pgd() with non-init_mm mm whilst still > > > walking kernel page table ranges. > > > > > > For x86 this is done in ptdump_curknl_show() and ptdump_efi_show(), the > > > first passing current->mm, and the second passing efi_mm (we reach kernel > > > mappings that init_mm protects for current->mm due to x86 cloning shared > > > kernel page tables for arbitrary mm's). > > > > > > arm64 does so via ptdump_debugfs_register(), configured by efi_ptdump_info > > > for efi ranges against efi_mm. > > > > > > The init_mm mmap lock is used to stabilise page table freeing against > > > ptdump, so take a nested lock on init_mm to ensure that we are correctly > > > stabilised. > > > > > > We take this after mmap write locking the non-init_mm mm. Nothing acquires > > > the init_mm lock first before locking an arbitrary mm, so no deadlock is > > > possible. > > > > > > Other fixes have been sent which update the two cases which can cause races > > > with ptdump in init_mm ranges to acquire the init_mm mmap write lock - vmap > > > and x86 CPA huge page promotion. > > > > > > For arm64, commit fa93b45fd397 ("arm64: Enable vmalloc-huge with ptdump") > > > already provides exclusion against init_mm for the vmap case, which this > > > patch also pairs with. > > > > > > The first point at which ptdump can race kernel page table freeing is > > > commit b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page > > > table"), so we target this in the Fixes tag. > > > > Does this have any known userspace impact? > > Taken in conjunction with the other fixes mentioned it resolves a UAF, so yes :) > > > > > > Fixes: b6bdb7517c3d ("mm/vmalloc: add interfaces to free unmapped page table") > > > > Since 2018, so I won't make this a hotfix, OK? > > > > No, this has to be a hotfix, it is part of solving a live UAF issue. > > Cheers, Lorenzo Have put this patch in a series in [0], as easier to just keep everything together and makes dependencies clear and what it's for. Cheers, Lorenzo [0]:https://lore.kernel.org/all/20260712-series-vmap-race-fix-v2-0-ad134cc3a12a@kernel.org/