---- 在 星期一, 2020-12-07 19:24:10 Dominique Martinet <asmadeus@xxxxxxxxxxxxx> 撰写 ---- > Chengguang Xu wrote on Mon, Dec 07, 2020: > > > , VM_MAYWRITE is set anytime we have a shared map where file has > > > been opened read-write, which seems to be what you want with regards to > > > protecting from mprotect calls. > > > > > > How about simply changing check from WRITE to MAYWRITE? > > > > It would be fine and based on the code in do_mmap(), it seems we even don't > > need extra check here. The condition (vma->vm_flags & VM_SHARED) will be enough. > > Am I missing something? > > VM_MAYWRITE is unset if the file hasn't been open for writing (in which > case the mapping can't be mprotect()ed to writable map), so checking it > is a bit more efficient. > > Anyway I'd like to obsolete the writeback fid uses now that fids have a > refcount (this usecase can be a simple refcount increase), in which case > efficiency is less of a problem, but we're not there yet... > > Please resend with MAYWRITE if you want authorship and I'll try to take > some time to test incl. the mprotect usecase. > Thanks for the review, I'll send revised version later. Thanks, Chengguang
