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 v2: - Turned the MMF_INIT_FLAGS macro into a mmf_init_flags function as suggested by David Hildenbrand - Removed the ability to transition from to PR_MDWE_REFUSE_EXEC_GAIN from (PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT) which also significantly simplifies the prctl_set_mdwe logic - Cc-ed -stable on patch 3 as suggested by Alexey Izbyshev - Added a handful of Reviewed-by/Acked-by trailers 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 | 32 +++++-- tools/include/uapi/linux/prctl.h | 3 +- tools/testing/selftests/mm/mdwe_test.c | 113 +++++++++++++++++++++---- 6 files changed, 139 insertions(+), 24 deletions(-) -- 2.41.0.255.g8b1d071c50-goog
