From: Lorenzo Stoakes <lstoakes@gmail.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Muchun Song <muchun.song@linux.dev>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Lorenzo Stoakes <lstoakes@gmail.com>
Subject: [RFC PATCH 0/3] permit write-sealed memfd read-only shared mappings
Date: Mon, 3 Apr 2023 23:28:29 +0100 [thread overview]
Message-ID: <cover.1680560277.git.lstoakes@gmail.com> (raw)
This patch series is in two parts:-
1. Currently there are a number of places in the kernel where we assume
VM_SHARED implies that a mapping is writable. Let's be slightly less
strict and relax this restriction in the case that VM_MAYWRITE is not
set.
This should have no noticeable impact as the lack of VM_MAYWRITE implies
that the mapping can not be made writable via mprotect() or any other
means.
2. Align the behaviour of F_SEAL_WRITE and F_SEAL_FUTURE_WRITE on mmap().
The latter already clears the VM_MAYWRITE flag for a sealed read-only
mapping, we simply extend this to F_SEAL_WRITE too.
For this to have effect, we must also invoke call_mmap() before
mapping_map_writable().
As this is quite a fundamental change on the assumptions around VM_SHARED
and since this causes a visible change to userland (in permitting read-only
shared mappings on F_SEAL_WRITE mappings), I am putting forward as an RFC
to see if there is anything terribly wrong with it.
I suspect even if the patch series as a whole is unpalatable, there are
probably things we can salvage from it in any case.
Thanks to Andy Lutomirski who inspired the series!
Lorenzo Stoakes (3):
mm: drop the assumption that VM_SHARED always implies writable
mm: update seal_check_[future_]write() to include F_SEAL_WRITE as well
mm: perform the mapping_map_writable() check after call_mmap()
fs/hugetlbfs/inode.c | 2 +-
include/linux/fs.h | 4 ++--
include/linux/mm.h | 24 ++++++++++++++++++------
kernel/fork.c | 2 +-
mm/filemap.c | 2 +-
mm/madvise.c | 2 +-
mm/mmap.c | 22 +++++++++++-----------
mm/shmem.c | 2 +-
8 files changed, 36 insertions(+), 24 deletions(-)
--
2.40.0
next reply other threads:[~2023-04-03 22:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-03 22:28 Lorenzo Stoakes [this message]
2023-04-03 22:28 ` [RFC PATCH 1/3] mm: drop the assumption that VM_SHARED always implies writable Lorenzo Stoakes
2023-04-03 22:28 ` [RFC PATCH 2/3] mm: update seal_check_[future_]write() to include F_SEAL_WRITE as well Lorenzo Stoakes
2023-04-03 22:28 ` [RFC PATCH 3/3] mm: perform the mapping_map_writable() check after call_mmap() Lorenzo Stoakes
2023-04-21 9:06 ` Jan Kara
2023-04-21 21:15 ` Lorenzo Stoakes
2023-04-21 9:01 ` [RFC PATCH 0/3] permit write-sealed memfd read-only shared mappings Jan Kara
2023-04-21 21:23 ` Lorenzo Stoakes
2023-04-24 12:19 ` Jan Kara
2023-04-24 12:23 ` Lorenzo Stoakes
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