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 04D0E5695 for ; Tue, 14 Jan 2025 00:19:48 +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=1736813989; cv=none; b=fi5vR2nafv1OdhkQ+wodC6f3KS/imn7eoutUtcxmnCv90R5SRTvMjesON0KaYkq9tjbcJ5aeYVJXOZL+i3o3iy4tvsjOIA5P2DBS0xl3XhmePPGThl85Uv+k86tyl6y+1gXgF9uQynl5BjwvomqZk/4zYkcW7WzmzdXkuRrqVQ4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736813989; c=relaxed/simple; bh=dikEt49AxZFPDdNOnN4kvTD6aqSqWvNq8OaRz/O2wEw=; h=Date:To:From:Subject:Message-Id; b=BCdtrW+b6tm3PHDUkCWLarBLmFpXsqrA1bhbnW0RDEWE9KTivErN5i42mlCejM86WIsGSNVG1LIbFjGC+m1UZPHU4ztHOvm6YEGoBmlZWaiKIr/S7XwYiCc6C8tjnphwk2QycQYqIHZI5rJrwQUo0/+0cjywRIDlfj0f5bKqmfQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=E/r9RMJY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="E/r9RMJY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 831C1C4CED6; Tue, 14 Jan 2025 00:19:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1736813988; bh=dikEt49AxZFPDdNOnN4kvTD6aqSqWvNq8OaRz/O2wEw=; h=Date:To:From:Subject:From; b=E/r9RMJYmPplIeUguuTBbN5lNV7jgNVha7WDLn9zaXfg1+7hrV76Kx+ls0ncPu/+q vqcuknjewsKfuGkX6sBBz65E/krOUsvgEW9Mym34kApuefuR6Axr/XGdnCagFSQP69 0yp+LDOSP+aRVI2KzLS6CK2jRlbbU3xYJBNnc9Sg= Date: Mon, 13 Jan 2025 16:19:47 -0800 To: mm-commits@vger.kernel.org,yosryahmed@google.com,ying.huang@linux.alibaba.com,v-songbaohua@oppo.com,ryan.roberts@arm.com,nphamcs@gmail.com,kaleshsingh@google.com,hughd@google.com,hannes@cmpxchg.org,chrisl@kernel.org,bhe@redhat.com,kasong@tencent.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage.patch added to mm-unstable branch Message-Id: <20250114001948.831C1C4CED6@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm, swap: hold a reference during scan and cleanup flag usage has been added to the -mm mm-unstable branch. Its filename is mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Kairui Song Subject: mm, swap: hold a reference during scan and cleanup flag usage Date: Tue, 14 Jan 2025 01:57:26 +0800 The flag SWP_SCANNING was used as an indicator of whether a device is being scanned for allocation, and prevents swapoff. Combined with SWP_WRITEOK, they work as a set of barriers for a clean swapoff: 1. Swapoff clears SWP_WRITEOK, allocation requests will see ~SWP_WRITEOK and abort as it's serialized by si->lock. 2. Swapoff unuses all allocated entries. 3. Swapoff waits for SWP_SCANNING flag to be cleared, so ongoing allocations will stop, preventing UAF. 4. Now swapoff can free everything safely. This will make the allocation path have a hard dependency on si->lock. Allocation always have to acquire si->lock first for setting SWP_SCANNING and checking SWP_WRITEOK. This commit removes this flag, and just uses the existing per-CPU refcount instead to prevent UAF in step 3, which serves well for such usage without dependency on si->lock, and scales very well too. Just hold a reference during the whole scan and allocation process. Swapoff will kill and wait for the counter. And for preventing any allocation from happening after step 1 so the unuse in step 2 can ensure all slots are free, swapoff will acquire the ci->lock of each cluster one by one to ensure all allocations see ~SWP_WRITEOK and abort. This way these dependences on si->lock are gone. And worth noting we can't kill the refcount as the first step for swapoff as the unuse process have to acquire the refcount. Link: https://lkml.kernel.org/r/20250113175732.48099-8-ryncsn@gmail.com Signed-off-by: Kairui Song Cc: Baoquan He Cc: Barry Song Cc: Chis Li Cc: "Huang, Ying" Cc: Hugh Dickens Cc: Johannes Weiner Cc: Kalesh Singh Cc: Nhat Pham Cc: Ryan Roberts Cc: Yosry Ahmed Signed-off-by: Andrew Morton --- include/linux/swap.h | 1 mm/swapfile.c | 90 +++++++++++++++++++++++++---------------- 2 files changed, 57 insertions(+), 34 deletions(-) --- a/include/linux/swap.h~mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage +++ a/include/linux/swap.h @@ -219,7 +219,6 @@ enum { SWP_STABLE_WRITES = (1 << 11), /* no overwrite PG_writeback pages */ SWP_SYNCHRONOUS_IO = (1 << 12), /* synchronous IO is efficient */ /* add others here before... */ - SWP_SCANNING = (1 << 14), /* refcount in scan_swap_map */ }; #define SWAP_CLUSTER_MAX 32UL --- a/mm/swapfile.c~mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage +++ a/mm/swapfile.c @@ -658,6 +658,8 @@ static bool cluster_alloc_range(struct s { unsigned int nr_pages = 1 << order; + lockdep_assert_held(&ci->lock); + if (!(si->flags & SWP_WRITEOK)) return false; @@ -1059,8 +1061,6 @@ static int cluster_alloc_swap(struct swa { int n_ret = 0; - si->flags += SWP_SCANNING; - while (n_ret < nr) { unsigned long offset = cluster_alloc_swap_entry(si, order, usage); @@ -1069,8 +1069,6 @@ static int cluster_alloc_swap(struct swa slots[n_ret++] = swp_entry(si->type, offset); } - si->flags -= SWP_SCANNING; - return n_ret; } @@ -1112,6 +1110,22 @@ static int scan_swap_map_slots(struct sw return cluster_alloc_swap(si, usage, nr, slots, order); } +static bool get_swap_device_info(struct swap_info_struct *si) +{ + if (!percpu_ref_tryget_live(&si->users)) + return false; + /* + * Guarantee the si->users are checked before accessing other + * fields of swap_info_struct, and si->flags (SWP_WRITEOK) is + * up to dated. + * + * Paired with the spin_unlock() after setup_swap_info() in + * enable_swap_info(), and smp_wmb() in swapoff. + */ + smp_rmb(); + return true; +} + int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order) { int order = swap_entry_order(entry_order); @@ -1139,13 +1153,16 @@ start_over: /* requeue si to after same-priority siblings */ plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]); spin_unlock(&swap_avail_lock); - spin_lock(&si->lock); - n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE, - n_goal, swp_entries, order); - spin_unlock(&si->lock); - if (n_ret || size > 1) - goto check_out; - cond_resched(); + if (get_swap_device_info(si)) { + spin_lock(&si->lock); + n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE, + n_goal, swp_entries, order); + spin_unlock(&si->lock); + put_swap_device(si); + if (n_ret || size > 1) + goto check_out; + cond_resched(); + } spin_lock(&swap_avail_lock); /* @@ -1296,16 +1313,8 @@ struct swap_info_struct *get_swap_device si = swp_swap_info(entry); if (!si) goto bad_nofile; - if (!percpu_ref_tryget_live(&si->users)) + if (!get_swap_device_info(si)) goto out; - /* - * Guarantee the si->users are checked before accessing other - * fields of swap_info_struct. - * - * Paired with the spin_unlock() after setup_swap_info() in - * enable_swap_info(). - */ - smp_rmb(); offset = swp_offset(entry); if (offset >= si->max) goto put_out; @@ -1785,10 +1794,13 @@ swp_entry_t get_swap_page_of_type(int ty goto fail; /* This is called for allocating swap entry, not cache */ - spin_lock(&si->lock); - if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry, 0)) - atomic_long_dec(&nr_swap_pages); - spin_unlock(&si->lock); + if (get_swap_device_info(si)) { + spin_lock(&si->lock); + if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry, 0)) + atomic_long_dec(&nr_swap_pages); + spin_unlock(&si->lock); + put_swap_device(si); + } fail: return entry; } @@ -2562,6 +2574,25 @@ bool has_usable_swap(void) return ret; } +/* + * Called after clearing SWP_WRITEOK, ensures cluster_alloc_range + * see the updated flags, so there will be no more allocations. + */ +static void wait_for_allocation(struct swap_info_struct *si) +{ + unsigned long offset; + unsigned long end = ALIGN(si->max, SWAPFILE_CLUSTER); + struct swap_cluster_info *ci; + + BUG_ON(si->flags & SWP_WRITEOK); + + for (offset = 0; offset < end; offset += SWAPFILE_CLUSTER) { + ci = lock_cluster(si, offset); + unlock_cluster(ci); + offset += SWAPFILE_CLUSTER; + } +} + SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) { struct swap_info_struct *p = NULL; @@ -2632,6 +2663,8 @@ SYSCALL_DEFINE1(swapoff, const char __us spin_unlock(&p->lock); spin_unlock(&swap_lock); + wait_for_allocation(p); + disable_swap_slots_cache_lock(); set_current_oom_origin(); @@ -2674,15 +2707,6 @@ SYSCALL_DEFINE1(swapoff, const char __us spin_lock(&p->lock); drain_mmlist(); - /* wait for anyone still in scan_swap_map_slots */ - while (p->flags >= SWP_SCANNING) { - spin_unlock(&p->lock); - spin_unlock(&swap_lock); - schedule_timeout_uninterruptible(1); - spin_lock(&swap_lock); - spin_lock(&p->lock); - } - swap_file = p->swap_file; p->swap_file = NULL; p->max = 0; _ Patches currently in -mm which might be from kasong@tencent.com are mm-memcontrol-avoid-duplicated-memcg-enable-check.patch mm-swap_cgroup-remove-swap_cgroup_cmpxchg.patch mm-swap_cgroup-remove-global-swap-cgroup-lock.patch mm-swap_cgroup-decouple-swap-cgroup-recording-and-clearing.patch mm-swap-minor-clean-up-for-swap-entry-allocation.patch mm-swap-fold-swap_info_get_cont-in-the-only-caller.patch mm-swap-remove-old-allocation-path-for-hdd.patch mm-swap-use-cluster-lock-for-hdd.patch mm-swap-clean-up-device-availability-check.patch mm-swap-clean-up-plist-removal-and-adding.patch mm-swap-hold-a-reference-during-scan-and-cleanup-flag-usage.patch mm-swap-use-an-enum-to-define-all-cluster-flags-and-wrap-flags-changes.patch mm-swap-reduce-contention-on-device-lock.patch mm-swap-simplify-percpu-cluster-updating.patch mm-swap-introduce-a-helper-for-retrieving-cluster-from-offset.patch mm-swap-use-a-global-swap-cluster-for-non-rotation-devices.patch mm-swap_slots-remove-slot-cache-for-freeing-path.patch