From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Date: Wed, 16 Nov 2022 10:26:44 +0000 Subject: [PATCH mm-unstable v1 05/20] mm: add early FAULT_FLAG_WRITE consistency checks Message-Id: <20221116102659.70287-6-david@redhat.com> List-Id: References: <20221116102659.70287-1-david@redhat.com> In-Reply-To: <20221116102659.70287-1-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, Linus Torvalds , Andrew Morton , Jason Gunthorpe , John Hubbard , Peter Xu , Greg Kroah-Hartman , Andrea Arcangeli , Hugh Dickins , Nadav Amit , Vlastimil Babka , Matthew Wilcox , Mike Kravetz , Muchun Song , Shuah Khan , Lucas Stach , David Airlie , Oded Gabbay , Arnd Bergmann , Christoph Hellwig , Alex Williamson , David Hildenbrand 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. Write faults without VM_MAYWRITE don't make any sense, and our maybe_mkwrite() logic could have hidden such abuse for now. 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. 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. Signed-off-by: David Hildenbrand --- mm/memory.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index e014435a87db..c4fa378ec2a0 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5170,6 +5170,14 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma, */ if (!is_cow_mapping(vma->vm_flags)) *flags &= ~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; } return 0; } -- 2.38.1