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Fri, 25 Nov 2022 13:37:27 -0800 (PST) From: Jann Horn To: security@kernel.org, Andrew Morton Cc: Yang Shi , David Hildenbrand , Peter Xu , John Hubbard , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 1/3] mm/khugepaged: Take the right locks for page table retraction Date: Fri, 25 Nov 2022 22:37:12 +0100 Message-Id: <20221125213714.4115729-1-jannh@google.com> X-Mailer: git-send-email 2.38.1.584.g0f3c55d4c2-goog MIME-Version: 1.0 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669412249; a=rsa-sha256; cv=none; b=MhISH7X1t1NZyFPjagX9Rwp7zJcbHAnplk1hYTXp3ySvSsQKIaU48c3l9288rUFvnzPTiy 7IV+Q4fy29b6cnROjFsUksNV0q6AgbwIp21QX/4xhrbKrVTMrPtP8ef/Y0G6yZmQkjKm6B JqkSa/Y8kiCmOIiVogd0WjFPrPq0e+M= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=BOwP2Wul; spf=pass (imf20.hostedemail.com: domain of jannh@google.com designates 209.85.128.41 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; 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Only one of these needs to be held, and it does not need to be held in exclusive mode. Under those circumstances, the rules for concurrent access to page table entries are: - Terminal page table entries (entries that don't point to another page table) can be arbitrarily changed under the page table lock, with the exception that they always need to be consistent for hardware page table walks and lockless_pages_from_mm(). This includes that they can be changed into non-terminal entries. - Non-terminal page table entries (which point to another page table) can not be modified; readers are allowed to READ_ONCE() an entry, verify that it is non-terminal, and then assume that its value will stay as-is. Retracting a page table involves modifying a non-terminal entry, so page-table-level locks are insufficient to protect against concurrent page table traversal; it requires taking all the higher-level locks under which it is possible to start a page walk in the relevant range in exclusive mode. The collapse_huge_page() path for anonymous THP already follows this rule, but the shmem/file THP path was getting it wrong, making it possible for concurrent rmap-based operations to cause corruption. Cc: stable@kernel.org Fixes: 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP") Signed-off-by: Jann Horn Acked-by: David Hildenbrand --- mm/khugepaged.c | 55 +++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 51 insertions(+), 4 deletions(-) base-commit: eb7081409f94a9a8608593d0fb63a1aa3d6f95d8 diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 4734315f79407..674b111a24fa7 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1384,16 +1384,37 @@ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr, return SCAN_SUCCEED; } +/* + * A note about locking: + * Trying to take the page table spinlocks would be useless here because those + * are only used to synchronize: + * + * - modifying terminal entries (ones that point to a data page, not to another + * page table) + * - installing *new* non-terminal entries + * + * Instead, we need roughly the same kind of protection as free_pgtables() or + * mm_take_all_locks() (but only for a single VMA): + * The mmap lock together with this VMA's rmap locks covers all paths towards + * the page table entries we're messing with here, except for hardware page + * table walks and lockless_pages_from_mm(). + */ static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, pmd_t *pmdp) { - spinlock_t *ptl; pmd_t pmd; mmap_assert_write_locked(mm); - ptl = pmd_lock(vma->vm_mm, pmdp); + if (vma->vm_file) + lockdep_assert_held_write(&vma->vm_file->f_mapping->i_mmap_rwsem); + /* + * All anon_vmas attached to the VMA have the same root and are + * therefore locked by the same lock. + */ + if (vma->anon_vma) + lockdep_assert_held_write(&vma->anon_vma->root->rwsem); + pmd = pmdp_collapse_flush(vma, addr, pmdp); - spin_unlock(ptl); mm_dec_nr_ptes(mm); page_table_check_pte_clear_range(mm, addr, pmd); pte_free(mm, pmd_pgtable(pmd)); @@ -1444,6 +1465,14 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false)) return SCAN_VMA_CHECK; + /* + * Symmetry with retract_page_tables(): Exclude MAP_PRIVATE mappings + * that got written to. Without this, we'd have to also lock the + * anon_vma if one exists. + */ + if (vma->anon_vma) + return SCAN_VMA_CHECK; + /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */ if (userfaultfd_wp(vma)) return SCAN_PTE_UFFD_WP; @@ -1477,6 +1506,20 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, goto drop_hpage; } + /* + * We need to lock the mapping so that from here on, only GUP-fast and + * hardware page walks can access the parts of the page tables that + * we're operating on. + * See collapse_and_free_pmd(). + */ + i_mmap_lock_write(vma->vm_file->f_mapping); + + /* + * This spinlock should be unnecessary: Nobody else should be accessing + * the page tables under spinlock protection here, only + * lockless_pages_from_mm() and the hardware page walker can access page + * tables while all the high-level locks are held in write mode. + */ start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl); result = SCAN_FAIL; @@ -1531,6 +1574,8 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, /* step 4: remove pte entries */ collapse_and_free_pmd(mm, vma, haddr, pmd); + i_mmap_unlock_write(vma->vm_file->f_mapping); + maybe_install_pmd: /* step 5: install pmd entry */ result = install_pmd @@ -1544,6 +1589,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, abort: pte_unmap_unlock(start_pte, ptl); + i_mmap_unlock_write(vma->vm_file->f_mapping); goto drop_hpage; } @@ -1600,7 +1646,8 @@ static int retract_page_tables(struct address_space *mapping, pgoff_t pgoff, * An alternative would be drop the check, but check that page * table is clear before calling pmdp_collapse_flush() under * ptl. It has higher chance to recover THP for the VMA, but - * has higher cost too. + * has higher cost too. It would also probably require locking + * the anon_vma. */ if (vma->anon_vma) { result = SCAN_PAGE_ANON; From patchwork Fri Nov 25 21:37:13 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jann Horn X-Patchwork-Id: 13056268 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]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEE9DC4332F for ; Fri, 25 Nov 2022 21:37:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 38E066B0081; Fri, 25 Nov 2022 16:37:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 33DCB6B0082; Fri, 25 Nov 2022 16:37:47 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1DEAD6B0083; Fri, 25 Nov 2022 16:37:47 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 114C56B0081 for ; 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Fri, 25 Nov 2022 13:37:44 -0800 (PST) From: Jann Horn To: security@kernel.org, Andrew Morton Cc: Yang Shi , David Hildenbrand , Peter Xu , John Hubbard , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 2/3] mm/khugepaged: Fix GUP-fast interaction by sending IPI Date: Fri, 25 Nov 2022 22:37:13 +0100 Message-Id: <20221125213714.4115729-2-jannh@google.com> X-Mailer: git-send-email 2.38.1.584.g0f3c55d4c2-goog In-Reply-To: <20221125213714.4115729-1-jannh@google.com> References: <20221125213714.4115729-1-jannh@google.com> MIME-Version: 1.0 ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669412266; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=SXD6TekHCwWyaJjEnEUCIQwhKm8R4syqj2EShSG9CG4=; b=p61AVqnmi4UbpmXnm25A9h+mfa3YwUfGeWqQoQkqdy6+COy2gOFvSzXChXxn5FkUrNr+RA +ftD1HeSwoKcNrD+dGLOkRPW6aXPM9CKSgKSdgU4yXQMI8ki16RKWTejb4n7QIyLVu/saY BguVthkx37z4gQObqKuz1V8L8OW79oI= ARC-Authentication-Results: i=1; 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However, lockless_pages_from_mm() still requires that the page table is not concurrently freed. Fix it by sending IPIs (if the architecture uses semi-RCU-style page table freeing) before freeing/reusing page tables. Cc: stable@kernel.org Fixes: ba76149f47d8 ("thp: khugepaged") Signed-off-by: Jann Horn Acked-by: David Hildenbrand --- replaced the mmu_gather-based scheme with an RCU call as suggested by Peter Xu include/asm-generic/tlb.h | 4 ++++ mm/khugepaged.c | 2 ++ mm/mmu_gather.c | 4 +--- 3 files changed, 7 insertions(+), 3 deletions(-) diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index 492dce43236ea..cab7cfebf40bd 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -222,12 +222,16 @@ extern void tlb_remove_table(struct mmu_gather *tlb, void *table); #define tlb_needs_table_invalidate() (true) #endif +void tlb_remove_table_sync_one(void); + #else #ifdef tlb_needs_table_invalidate #error tlb_needs_table_invalidate() requires MMU_GATHER_RCU_TABLE_FREE #endif +static inline void tlb_remove_table_sync_one(void) { } + #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */ diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 674b111a24fa7..c3d3ce596bff7 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1057,6 +1057,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, _pmd = pmdp_collapse_flush(vma, address, pmd); spin_unlock(pmd_ptl); mmu_notifier_invalidate_range_end(&range); + tlb_remove_table_sync_one(); spin_lock(pte_ptl); result = __collapse_huge_page_isolate(vma, address, pte, cc, @@ -1415,6 +1416,7 @@ static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *v lockdep_assert_held_write(&vma->anon_vma->root->rwsem); pmd = pmdp_collapse_flush(vma, addr, pmdp); + tlb_remove_table_sync_one(); mm_dec_nr_ptes(mm); page_table_check_pte_clear_range(mm, addr, pmd); pte_free(mm, pmd_pgtable(pmd)); diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index add4244e5790d..3a2c3f8cad2fe 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -153,7 +153,7 @@ static void tlb_remove_table_smp_sync(void *arg) /* Simply deliver the interrupt */ } -static void tlb_remove_table_sync_one(void) +void tlb_remove_table_sync_one(void) { /* * This isn't an RCU grace period and hence the page-tables cannot be @@ -177,8 +177,6 @@ static void tlb_remove_table_free(struct mmu_table_batch *batch) #else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */ -static void tlb_remove_table_sync_one(void) { } - static void tlb_remove_table_free(struct mmu_table_batch *batch) { __tlb_remove_table_free(batch); 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Fri, 25 Nov 2022 13:37:46 -0800 (PST) From: Jann Horn To: security@kernel.org, Andrew Morton Cc: Yang Shi , David Hildenbrand , Peter Xu , John Hubbard , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 3/3] mm/khugepaged: Invoke MMU notifiers in shmem/file collapse paths Date: Fri, 25 Nov 2022 22:37:14 +0100 Message-Id: <20221125213714.4115729-3-jannh@google.com> X-Mailer: git-send-email 2.38.1.584.g0f3c55d4c2-goog In-Reply-To: <20221125213714.4115729-1-jannh@google.com> References: <20221125213714.4115729-1-jannh@google.com> MIME-Version: 1.0 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669412268; a=rsa-sha256; cv=none; b=fScZXLhIoGO+qGuaX2+mHGZnfHe+oY4mY2p3kqNIMZBlyTVqe8cECbvqODfgVQmeGqW5c9 2oMJ/m9nKZicJXbWJ5bDZXOh6MJpHGbxW580Fk/tNaGzXYk0clXBiyThBoQeEdzNLJnYn+ iuEjFfKKgHZIIVfj3GH4BHerAKnBusM= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=F18wqhUO; spf=pass (imf06.hostedemail.com: domain of jannh@google.com designates 209.85.221.52 as permitted sender) smtp.mailfrom=jannh@google.com; 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Secondary MMUs don't hold their own references to pages that are mirrored over, so failing to notify them can lead to page use-after-free. I'm marking this as addressing an issue introduced in commit f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of the security impact of this only came in commit 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP"), which actually omitted flushes for the removal of present PTEs, not just for the removal of empty page tables. Cc: stable@kernel.org Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Jann Horn --- mm/khugepaged.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index c3d3ce596bff7..49eb4b4981d88 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1404,6 +1404,7 @@ static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *v unsigned long addr, pmd_t *pmdp) { pmd_t pmd; + struct mmu_notifier_range range; mmap_assert_write_locked(mm); if (vma->vm_file) @@ -1415,8 +1416,12 @@ static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *v if (vma->anon_vma) lockdep_assert_held_write(&vma->anon_vma->root->rwsem); + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, addr, + addr + HPAGE_PMD_SIZE); + mmu_notifier_invalidate_range_start(&range); pmd = pmdp_collapse_flush(vma, addr, pmdp); tlb_remove_table_sync_one(); + mmu_notifier_invalidate_range_end(&range); mm_dec_nr_ptes(mm); page_table_check_pte_clear_range(mm, addr, pmd); pte_free(mm, pmd_pgtable(pmd));