From: Nadav Amit <namit@vmware.com>
To: David Hildenbrand <david@redhat.com>
Cc: "dri-devel@lists.freedesktop.org"
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Mike Kravetz <mike.kravetz@oracle.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH RFC 05/19] mm: add early FAULT_FLAG_WRITE consistency checks
Date: Mon, 7 Nov 2022 19:03:48 +0000 [thread overview]
Message-ID: <E1E8C21A-EAEB-4FA3-A9B9-1DFF81FCDA70@vmware.com> (raw)
In-Reply-To: <20221107161740.144456-6-david@redhat.com>
On Nov 7, 2022, at 8:17 AM, David Hildenbrand <david@redhat.com> wrote:
> !! External Email
>
> Let's catch abuse of FAULT_FLAG_WRITE early, such that we don't have to
> care in all other handlers and might get "surprises" if we forget to do
> so.
>
> Write faults without VM_MAYWRITE don't make any sense, and our
> maybe_mkwrite() logic could have hidden such abuse for now.
>
> Write faults without VM_WRITE on something that is not a COW mapping is
> similarly broken, and e.g., do_wp_page() could end up placing an
> anonymous page into a shared mapping, which would be bad.
>
> This is a preparation for reliable R/O long-term pinning of pages in
> private mappings, whereby we want to make sure that we will never break
> COW in a read-only private mapping.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> mm/memory.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index fe131273217a..826353da7b23 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5159,6 +5159,14 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
> */
> if (!is_cow_mapping(vma->vm_flags))
> *flags &= ~FAULT_FLAG_UNSHARE;
> + } else if (*flags & FAULT_FLAG_WRITE) {
> + /* Write faults on read-only mappings are impossible ... */
> + if (WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE)))
> + return VM_FAULT_SIGSEGV;
> + /* ... and FOLL_FORCE only applies to COW mappings. */
> + if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) &&
> + !is_cow_mapping(vma->vm_flags)))
> + return VM_FAULT_SIGSEGV;
Not sure about the WARN_*(). Seems as if it might trigger in benign even if
rare scenarios, e.g., mprotect() racing with page-fault.
next prev parent reply other threads:[~2022-11-07 19:03 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-07 16:17 [PATCH RFC 00/19] mm/gup: remove FOLL_FORCE usage from drivers (reliable R/O long-term pinning) David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 01/19] selftests/vm: anon_cow: prepare for non-anonymous COW tests David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 02/19] selftests/vm: cow: basic COW tests for non-anonymous pages David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 03/19] selftests/vm: cow: R/O long-term pinning reliability tests for non-anon pages David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 04/19] mm: add early FAULT_FLAG_UNSHARE consistency checks David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 05/19] mm: add early FAULT_FLAG_WRITE " David Hildenbrand
2022-11-07 19:03 ` Nadav Amit [this message]
2022-11-07 19:27 ` David Hildenbrand
2022-11-07 19:50 ` Nadav Amit
2022-11-07 16:17 ` [PATCH RFC 06/19] mm: rework handling in do_wp_page() based on private vs. shared mappings David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 07/19] mm: don't call vm_ops->huge_fault() in wp_huge_pmd()/wp_huge_pud() for private mappings David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 08/19] mm: extend FAULT_FLAG_UNSHARE support to anything in a COW mapping David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 09/19] mm/gup: reliable R/O long-term pinning in COW mappings David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 10/19] RDMA/umem: remove FOLL_FORCE usage David Hildenbrand
2022-11-14 8:30 ` Leon Romanovsky
2022-11-07 16:17 ` [PATCH RFC 11/19] RDMA/usnic: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 12/19] RDMA/siw: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 13/19] media: videobuf-dma-sg: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 14/19] drm/etnaviv: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 15/19] media: pci/ivtv: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 16/19] mm/frame-vector: " David Hildenbrand
2022-11-08 4:45 ` Tomasz Figa
2022-11-08 9:40 ` David Hildenbrand
2022-11-22 12:25 ` Hans Verkuil
2022-11-22 12:38 ` David Hildenbrand
2022-11-22 14:07 ` Hans Verkuil
2022-11-22 15:03 ` David Hildenbrand
2022-11-22 17:33 ` Linus Torvalds
2022-11-07 16:17 ` [PATCH RFC 17/19] drm/exynos: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 18/19] RDMA/hw/qib/qib_user_pages: " David Hildenbrand
2022-11-07 16:17 ` [PATCH RFC 19/19] habanalabs: " David Hildenbrand
2022-11-07 21:25 ` Oded Gabbay
2022-11-07 17:27 ` [PATCH RFC 00/19] mm/gup: remove FOLL_FORCE usage from drivers (reliable R/O long-term pinning) Linus Torvalds
2022-11-08 9:29 ` David Hildenbrand
[not found] ` <Y3HaGbPcGfTxlLPZ@infradead.org>
2022-11-14 8:07 ` David Hildenbrand
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