mprotect (nr 10)

Linux Signature

int mprotect(void *addr, size_t len, int prot);

Description

Changes the access protections for the calling process’s memory pages in the range [addr, addr+len).

Implementation

1. Validates addr is page-aligned and len > 0 (returns -EINVAL otherwise).
2. Aligns len up to the next page boundary.
3. Splits/updates VMAs in the range via Process::mprotect_vmas():
   • Entire VMA overlap: updates prot in place.
   • Partial overlap (front, tail, middle): splits VMA and sets new prot on the affected portion.
4. Converts prot to x86-64 page table flags (prot_to_page_flags()):
   • PROT_NONE → USER_ACCESSIBLE only (no PRESENT — any access faults).
   • PROT_READ → PRESENT | USER_ACCESSIBLE | NO_EXECUTE.
   • PROT_WRITE → adds WRITABLE.
   • PROT_EXEC → removes NO_EXECUTE.
5. Updates page table entries via MemoryServices::update_user_page_flags() with TLB flush.
6. Returns 0 on success.

Lock ordering: PROCESS_TABLE first (VMA split), then MEMORY (page table update).

Returns 0 (no-op) if no VMAs overlap the requested range (Linux semantics).

Source: osl/src/syscalls/mem.rs (sys_mprotect), libkernel/src/process.rs (mprotect_vmas), libkernel/src/memory/mod.rs (update_user_page_flags)