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.
[1] https://lore.kernel.org/all/20240817-mseal-depessimize-v3-0-d8d2e037df30@gma...
Fixes: 4a2dd02b0916 ("mm/mprotect: replace can_modify_mm with can_modify_vma") Signed-off-by: Jeff Xu jeffxu@chromium.org --- mm/mprotect.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/mprotect.c b/mm/mprotect.c index 516b1d847e2c..a24d23967aa5 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -613,14 +613,14 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb, unsigned long charged = 0; int error;
- if (!can_modify_vma(vma)) - return -EPERM; - if (newflags == oldflags) { *pprev = vma; return 0; }
+ if (!can_modify_vma(vma)) + return -EPERM; + /* * Do PROT_NONE PFN permission checks here when we can still * bail out without undoing a lot of state. This is a rather