[PATCH v2 0/5] MDWE without inheritance

Florent Revest
2023-05-17T15:05:14Z

Joey recently introduced a Memory-Deny-Write-Executable (MDWE) prctl which tags
current with a flag that prevents pages that were previously not executable from
becoming executable.
This tag always gets inherited by children tasks. (it's in MMF_INIT_MASK)

At Google, we've been using a somewhat similar downstream patch for a few years
now. To make the adoption of this feature easier, we've had it support a mode in
which the W^X flag does not propagate to children. For example, this is handy if
a C process which wants W^X protection suspects it could start children
processes that would use a JIT.

I'd like to align our features with the upstream prctl. This series proposes a
new NO_INHERIT flag to the MDWE prctl to make this kind of adoption easier. It
sets a different flag in current that is not in MMF_INIT_MASK and which does not
propagate.

As part of looking into MDWE, I also fixed a couple of things in the MDWE test.

This series applies on the mm-everything-2023-05-16-23-30 tag of the mm tree:
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/

Diff since v1:
- MMF_HAS_MDWE_NO_INHERIT clears MMF_HAS_MDWE in the fork path as part of a
MMF_INIT_FLAGS macro (suggested by Catalin)
- PR_MDWE_* are defined as unsigned long rather than int (suggested by Andrey)

Florent Revest (5):
kselftest: vm: Fix tabs/spaces inconsistency in the mdwe test
kselftest: vm: Fix mdwe's mmap_FIXED test case
mm: Make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long
mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl
kselftest: vm: Add tests for no-inherit memory-deny-write-execute

include/linux/sched/coredump.h | 10 +++
include/uapi/linux/prctl.h | 3 +-
kernel/fork.c | 2 +-
kernel/sys.c | 24 +++++-
tools/include/uapi/linux/prctl.h | 3 +-
tools/testing/selftests/mm/mdwe_test.c | 110 +++++++++++++++++++++----
6 files changed, 131 insertions(+), 21 deletions(-)

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2.40.1.606.ga4b1b128d6-goog