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mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none Received: from DM6PR12MB3834.namprd12.prod.outlook.com (2603:10b6:5:14a::12) by DM6PR12MB3403.namprd12.prod.outlook.com (2603:10b6:5:11d::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3499.24; Fri, 30 Oct 2020 14:46:23 +0000 Received: from DM6PR12MB3834.namprd12.prod.outlook.com ([fe80::cdbe:f274:ad65:9a78]) by DM6PR12MB3834.namprd12.prod.outlook.com ([fe80::cdbe:f274:ad65:9a78%7]) with mapi id 15.20.3499.027; Fri, 30 Oct 2020 14:46:23 +0000 From: Jason Gunthorpe To: , Peter Xu , Linus Torvalds CC: Andrea Arcangeli , Andrew Morton , Aneesh Kumar K.V , Christoph Hellwig , Hugh Dickins , Jan Kara , Jann Horn , John Hubbard , Kirill Shutemov , Kirill Tkhai , Leon Romanovsky , Linux-MM , Michal Hocko , Oleg Nesterov Subject: [PATCH v2 2/2] mm: prevent gup_fast from racing with COW during fork Date: Fri, 30 Oct 2020 11:46:21 -0300 Message-ID: <2-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> In-Reply-To: <0-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> References: X-ClientProxiedBy: BL0PR0102CA0056.prod.exchangelabs.com (2603:10b6:208:25::33) To DM6PR12MB3834.namprd12.prod.outlook.com (2603:10b6:5:14a::12) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (156.34.48.30) by BL0PR0102CA0056.prod.exchangelabs.com (2603:10b6:208:25::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3499.19 via Frontend Transport; Fri, 30 Oct 2020 14:46:23 +0000 Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kYVfa-00DEq3-3W; Fri, 30 Oct 2020 11:46:22 -0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1604069187; bh=d89KBJlCcce0uUOFM90L9lMb/6UXmKWJc/WASdjPs80=; h=ARC-Seal:ARC-Message-Signature:ARC-Authentication-Results:From:To: CC:Subject:Date:Message-ID:In-Reply-To:References: Content-Transfer-Encoding:Content-Type:X-ClientProxiedBy: MIME-Version:X-MS-Exchange-MessageSentRepresentingType; b=OTdYVMDogdxSVuV1TYq9imzmQ9UI4XbTouktIfGwEku5mI3HmV3gZ6Sre5CBNmRLM M0oS5+18V0o2xN6Uxrn7rNXzggFqoXnKOJT39AXzZCzWxR9mFLHsopGzht66RXptwO Sd6L8q5gyRmXpeOtLW0kBOTRtCqNHLsgXn9BX51WbzsmAIMpF2dXR+Djnr70zTKwLy J6C2/9hzBC8zhq2wfwJQK+aQJQsIb+pdMXTx50TL1mTNsy5j37oD6WneWBv5YUaI/L tPXC5FCCxWg3CuAq3BPeGO0SpOk3yUlfqWwfiCfy5mNwIiXIejmL+Fs6WLahLmAP+/ hNPZAHnxZQ35Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Since commit 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") pages under a FOLL_PIN will not be write protected during COW for fork. This means that pages returned from pin_user_pages(FOLL_WRITE) should not become write protected while the pin is active. However, there is a small race where get_user_pages_fast(FOLL_PIN) can establish a FOLL_PIN at the same time copy_present_page() is write protecting it: CPU 0 CPU 1 get_user_pages_fast() internal_get_user_pages_fast() copy_page_range() pte_alloc_map_lock() copy_present_page() atomic_read(has_pinned) == 0 page_maybe_dma_pinned() == false atomic_set(has_pinned, 1); gup_pgd_range() gup_pte_range() pte_t pte = gup_get_pte(ptep) pte_access_permitted(pte) try_grab_compound_head() pte = pte_wrprotect(pte) set_pte_at(); pte_unmap_unlock() // GUP now returns with a write protected page The first attempt to resolve this by using the write protect caused problems (and was missing a barrrier), see commit f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Instead wrap copy_p4d_range() with the write side of a seqcount and check the read side around gup_pgd_range(). If there is a collision then get_user_pages_fast() fails and falls back to slow GUP. Slow GUP is safe against this race because copy_page_range() is only called while holding the exclusive side of the mmap_lock on the src mm_struct. Fixes: f3c64eda3e50 ("mm: avoid early COW write protect games during fork()") Suggested-by: Linus Torvalds Link: https://lore.kernel.org/r/CAHk-=wi=iCnYCARbPGjkVJu9eyYeZ13N64tZYLdOB8CP5Q_PLw@mail.gmail.com Reviewed-by: John Hubbard Signed-off-by: Jason Gunthorpe Reviewed-by: Jan Kara Reported-by: Jason Gunthorpe Reported-by: John Hubbard Reported-by: Linus Torvalds Signed-off-by: Ahmed S. Darwish Signed-off-by: Ahmed S. Darwish --- arch/x86/kernel/tboot.c | 1 + drivers/firmware/efi/efi.c | 1 + include/linux/mm_types.h | 7 +++++++ kernel/fork.c | 1 + mm/gup.c | 19 +++++++++++++++++++ mm/init-mm.c | 1 + mm/memory.c | 10 +++++++++- 7 files changed, 39 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c index 992fb1415c0f1f..6a2f542d9588a4 100644 --- a/arch/x86/kernel/tboot.c +++ b/arch/x86/kernel/tboot.c @@ -93,6 +93,7 @@ static struct mm_struct tboot_mm = { .pgd = swapper_pg_dir, .mm_users = ATOMIC_INIT(2), .mm_count = ATOMIC_INIT(1), + .write_protect_seq = SEQCNT_ZERO(tboot_mm.write_protect_seq), MMAP_LOCK_INITIALIZER(init_mm) .page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock), .mmlist = LIST_HEAD_INIT(init_mm.mmlist), diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index 5e5480a0a32d7d..2520f6e05f4d44 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -57,6 +57,7 @@ struct mm_struct efi_mm = { .mm_rb = RB_ROOT, .mm_users = ATOMIC_INIT(2), .mm_count = ATOMIC_INIT(1), + .write_protect_seq = SEQCNT_ZERO(efi_mm.write_protect_seq), MMAP_LOCK_INITIALIZER(efi_mm) .page_table_lock = __SPIN_LOCK_UNLOCKED(efi_mm.page_table_lock), .mmlist = LIST_HEAD_INIT(efi_mm.mmlist), diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 5a9238f6caad97..f13beacda6fd23 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -14,6 +14,7 @@ #include #include #include +#include #include @@ -446,6 +447,12 @@ struct mm_struct { */ atomic_t has_pinned; + /** + * @write_protect_seq: Odd when any thread is write protecting + * pages in this mm, for instance during fork(). + */ + seqcount_t write_protect_seq; + #ifdef CONFIG_MMU atomic_long_t pgtables_bytes; /* PTE page table pages */ #endif diff --git a/kernel/fork.c b/kernel/fork.c index 32083db7a2a23e..6fd934a6d60d96 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1007,6 +1007,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, mm->vmacache_seqnum = 0; atomic_set(&mm->mm_users, 1); atomic_set(&mm->mm_count, 1); + seqcount_init(&mm->write_protect_seq); mmap_init_lock(mm); INIT_LIST_HEAD(&mm->mmlist); mm->core_state = NULL; diff --git a/mm/gup.c b/mm/gup.c index 150cc962c99201..7944749ed7252f 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2678,11 +2678,18 @@ static unsigned long lockless_pages_from_mm(unsigned long start, { unsigned long flags; int nr_pinned = 0; + unsigned seq; if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) || !gup_fast_permitted(start, end)) return 0; + if (gup_flags & FOLL_PIN) { + seq = raw_read_seqcount(¤t->mm->write_protect_seq); + if (seq & 1) + return 0; + } + /* * Disable interrupts. The nested form is used, in order to allow full, * general purpose use of this routine. @@ -2697,6 +2704,18 @@ static unsigned long lockless_pages_from_mm(unsigned long start, local_irq_save(flags); gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); local_irq_restore(flags); + + /* + * When pinning pages for DMA there could be a concurrent write protect + * from fork() via copy_page_range(), in this case always fail fast GUP. + */ + if (gup_flags & FOLL_PIN) { + if (read_seqcount_t_retry(¤t->mm->write_protect_seq, + seq)) { + unpin_user_pages(pages, nr_pinned); + return 0; + } + } return nr_pinned; } diff --git a/mm/init-mm.c b/mm/init-mm.c index 3a613c85f9ede2..153162669f8062 100644 --- a/mm/init-mm.c +++ b/mm/init-mm.c @@ -31,6 +31,7 @@ struct mm_struct init_mm = { .pgd = swapper_pg_dir, .mm_users = ATOMIC_INIT(2), .mm_count = ATOMIC_INIT(1), + .write_protect_seq = SEQCNT_ZERO(init_mm.write_protect_seq), MMAP_LOCK_INITIALIZER(init_mm) .page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock), .arg_lock = __SPIN_LOCK_UNLOCKED(init_mm.arg_lock), diff --git a/mm/memory.c b/mm/memory.c index c48f8df6e50268..294c2c3c4fe00d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1171,6 +1171,12 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE, 0, src_vma, src_mm, addr, end); mmu_notifier_invalidate_range_start(&range); + /* + * The read side doesn't spin, it goes to the mmap_lock, so the + * raw version is used to avoid disabling preemption here + */ + mmap_assert_write_locked(src_mm); + raw_write_seqcount_t_begin(&src_mm->write_protect_seq); } ret = 0; @@ -1187,8 +1193,10 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) } } while (dst_pgd++, src_pgd++, addr = next, addr != end); - if (is_cow) + if (is_cow) { + raw_write_seqcount_t_end(&src_mm->write_protect_seq); mmu_notifier_invalidate_range_end(&range); + } return ret; }