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Lorenzo Stoakes 8ec396d05d mm: reinstate ability to map write-sealed memfd mappings read-only 
Patch series "mm: reinstate ability to map write-sealed memfd mappings
read-only".

In commit 158978945f ("mm: perform the mapping_map_writable() check
after call_mmap()") (and preceding changes in the same series) it became
possible to mmap() F_SEAL_WRITE sealed memfd mappings read-only.

Commit 5de195060b ("mm: resolve faulty mmap_region() error path
behaviour") unintentionally undid this logic by moving the
mapping_map_writable() check before the shmem_mmap() hook is invoked,
thereby regressing this change.

This series reworks how we both permit write-sealed mappings being mapped
read-only and disallow mprotect() from undoing the write-seal, fixing this
regression.

We also add a regression test to ensure that we do not accidentally
regress this in future.

Thanks to Julian Orth for reporting this regression.


This patch (of 2):

In commit 158978945f ("mm: perform the mapping_map_writable() check
after call_mmap()") (and preceding changes in the same series) it became
possible to mmap() F_SEAL_WRITE sealed memfd mappings read-only.

This was previously unnecessarily disallowed, despite the man page
documentation indicating that it would be, thereby limiting the usefulness
of F_SEAL_WRITE logic.

We fixed this by adapting logic that existed for the F_SEAL_FUTURE_WRITE
seal (one which disallows future writes to the memfd) to also be used for
F_SEAL_WRITE.

For background - the F_SEAL_FUTURE_WRITE seal clears VM_MAYWRITE for a
read-only mapping to disallow mprotect() from overriding the seal - an
operation performed by seal_check_write(), invoked from shmem_mmap(), the
f_op->mmap() hook used by shmem mappings.

By extending this to F_SEAL_WRITE and critically - checking
mapping_map_writable() to determine if we may map the memfd AFTER we
invoke shmem_mmap() - the desired logic becomes possible.  This is because
mapping_map_writable() explicitly checks for VM_MAYWRITE, which we will
have cleared.

Commit 5de195060b ("mm: resolve faulty mmap_region() error path
behaviour") unintentionally undid this logic by moving the
mapping_map_writable() check before the shmem_mmap() hook is invoked,
thereby regressing this change.

We reinstate this functionality by moving the check out of shmem_mmap()
and instead performing it in do_mmap() at the point at which VMA flags are
being determined, which seems in any case to be a more appropriate place
in which to make this determination.

In order to achieve this we rework memfd seal logic to allow us access to
this information using existing logic and eliminate the clearing of
VM_MAYWRITE from seal_check_write() which we are performing in do_mmap()
instead.

Link: https://lkml.kernel.org/r/99fc35d2c62bd2e05571cf60d9f8b843c56069e0.1732804776.git.lorenzo.stoakes@oracle.com
Fixes: 5de195060b ("mm: resolve faulty mmap_region() error path behaviour")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: Julian Orth <ju.orth@gmail.com>
Closes: https://lore.kernel.org/all/CAHijbEUMhvJTN9Xw1GmbM266FXXv=U7s4L_Jem5x3AaPZxrYpQ@mail.gmail.com/
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-12-30 17:59:06 -08:00
arch KVM x86 fixes for 6.13: 2024-12-22 12:16:41 -08:00
block block: avoid to reuse hctx not removed from cpuhp callback list 2024-12-18 07:25:37 -07:00
certs
crypto crypto: rsassa-pkcs1 - Copy source data for SG list 2024-12-10 13:34:05 +08:00
Documentation Devicetree fixes for 6.13, part 1: 2024-12-22 08:40:23 -08:00
drivers Devicetree fixes for 6.13, part 1: 2024-12-22 08:40:23 -08:00
fs 25 hotfixes. 16 are cc:stable. 19 are MM and 6 are non-MM. 2024-12-21 15:31:56 -08:00
include mm: reinstate ability to map write-sealed memfd mappings read-only 2024-12-30 17:59:06 -08:00
init
io_uring io_uring: check if iowq is killed before queuing 2024-12-19 13:31:53 -07:00
ipc
kernel 25 hotfixes. 16 are cc:stable. 19 are MM and 6 are non-MM. 2024-12-21 15:31:56 -08:00
lib alloc_tag: fix module allocation tags populated area calculation 2024-12-18 19:04:46 -08:00
LICENSES
mm mm: reinstate ability to map write-sealed memfd mappings read-only 2024-12-30 17:59:06 -08:00
net BPF fixes: 2024-12-21 11:07:19 -08:00
rust Including fixes from can and netfilter. 2024-12-19 09:19:11 -08:00
samples BPF fixes: 2024-12-06 15:07:48 -08:00
scripts Kbuild fixes for v6.13 (2nd) 2024-12-21 11:24:32 -08:00
security selinux/stable-6.13 PR 20241217 2024-12-18 12:10:15 -08:00
sound soc: fixes for 6.13 2024-12-16 10:10:53 -08:00
tools 25 hotfixes. 16 are cc:stable. 19 are MM and 6 are non-MM. 2024-12-21 15:31:56 -08:00
usr kbuild: Drop support for include/asm-<arch> in headers_check.pl 2024-12-21 11:43:17 +09:00
virt
.clang-format
.clippy.toml
.cocciconfig
.editorconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap mailmap: add entry for Ying Huang 2024-12-18 19:04:41 -08:00
.rustfmt.toml
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS drm fixes for 6.13-rc4 2024-12-20 10:17:53 -08:00
Makefile Linux 6.13-rc4 2024-12-22 13:22:21 -08:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.