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arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf11.hostedemail.com: domain of namit@vmware.com designates 52.101.64.12 as permitted sender) smtp.mailfrom=namit@vmware.com; dmarc=pass (policy=quarantine) header.from=vmware.com X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: x9rpkfc9ztxdswawo49unbudtziwguq5 X-HE-Tag: 1667847831-144195 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Nov 7, 2022, at 8:17 AM, David Hildenbrand wrote: > !! External Email >=20 > Let's catch abuse of FAULT_FLAG_WRITE early, such that we don't have to > care in all other handlers and might get "surprises" if we forget to do > so. >=20 > Write faults without VM_MAYWRITE don't make any sense, and our > maybe_mkwrite() logic could have hidden such abuse for now. >=20 > Write faults without VM_WRITE on something that is not a COW mapping is > similarly broken, and e.g., do_wp_page() could end up placing an > anonymous page into a shared mapping, which would be bad. >=20 > This is a preparation for reliable R/O long-term pinning of pages in > private mappings, whereby we want to make sure that we will never break > COW in a read-only private mapping. >=20 > Signed-off-by: David Hildenbrand > --- > mm/memory.c | 8 ++++++++ > 1 file changed, 8 insertions(+) >=20 > diff --git a/mm/memory.c b/mm/memory.c > index fe131273217a..826353da7b23 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5159,6 +5159,14 @@ static vm_fault_t sanitize_fault_flags(struct vm_a= rea_struct *vma, > */ > if (!is_cow_mapping(vma->vm_flags)) > *flags &=3D ~FAULT_FLAG_UNSHARE; > + } else if (*flags & FAULT_FLAG_WRITE) { > + /* Write faults on read-only mappings are impossible ... = */ > + if (WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE))) > + return VM_FAULT_SIGSEGV; > + /* ... and FOLL_FORCE only applies to COW mappings. */ > + if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) && > + !is_cow_mapping(vma->vm_flags))) > + return VM_FAULT_SIGSEGV; Not sure about the WARN_*(). Seems as if it might trigger in benign even if rare scenarios, e.g., mprotect() racing with page-fault.