From: Jeff Xu jeffxu@chromium.org
Initially, when mseal was introduced in 6.10, semantically, when a VMA within the specified address range is sealed, the mprotect will be rejected, leaving all of VMA unmodified. However, adding an extra loop to check the mseal flag for every VMA slows things down a bit, therefore in 6.12, this issue was solved by removing can_modify_mm and checking each VMA’s mseal flag directly without an extra loop [1]. This is a semantic change, i.e. partial update is allowed, VMAs can be updated until a sealed VMA is found.
The new semantic also means, we could allow mprotect on a sealed VMA if the new attribute of VMA remains the same as the old one. Relaxing this avoids unnecessary impacts for applications that want to seal a particular mapping. Doing this also has no security impact.
The mseal_test is also modified by this patch to adapt to the new semantic. Please note, mseal_test is currently undergoing refactoring, and eventually will be replaced with a new memory sealing selftest. In this patch, I only make a minimum change to make it pass. I considered adding a new testcase in mseal_test to cover this new behavior, however, the existing mseal_test is using wrong patterns and won’t pass the review. Such a new test is better to be added in the new refactored memory sealing tests. The refactoring is currently pending review [2].
[1] https://lore.kernel.org/all/20240817-mseal-depessimize-v3-0-d8d2e037df30@gma... [2] https://lore.kernel.org/all/20241211053311.245636-1-jeffxu@google.com/
Jeff Xu (2): selftests/mm: mseal_test: avoid using no-op mprotect mseal: allow noop mprotect
mm/mprotect.c | 6 +++--- tools/testing/selftests/mm/mseal_test.c | 6 +++--- 2 files changed, 6 insertions(+), 6 deletions(-)