From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48035C0502C for ; Mon, 29 Aug 2022 11:25:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231916AbiH2LZB (ORCPT ); Mon, 29 Aug 2022 07:25:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232108AbiH2LYU (ORCPT ); Mon, 29 Aug 2022 07:24:20 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AA04E5F986; Mon, 29 Aug 2022 04:15:17 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id C69A0B80F92; Mon, 29 Aug 2022 11:07:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF1FCC433C1; Mon, 29 Aug 2022 11:07:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1661771258; bh=+6fmvp2c8S1VZMDzHF7AuaBHo0zZ6cBpda3+aSMaIfk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ldMTFut+R0y7pUj3gHrXs8ssZFHHooCU00NNtY3JHz9LYT+6vTiaus6xd4eU0Lpgk bOur0TBtJEf4SNxoyBRjkvLJRYnS0r/hNa1f6F+gVJptZkGAzmIWKkafflEdSe/MqI bp4CwEW7ghjgl+8z/e5HKulFd8lgkBu4EqWENXcs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Hildenbrand , Mike Kravetz , Bjorn Helgaas , Cyrill Gorcunov , Hugh Dickins , Jamie Liu , "Kirill A. Shutemov" , Muchun Song , Naoya Horiguchi , Pavel Emelyanov , Peter Feiner , Peter Xu , Andrew Morton Subject: [PATCH 5.19 010/158] mm/hugetlb: support write-faults in shared mappings Date: Mon, 29 Aug 2022 12:57:40 +0200 Message-Id: <20220829105809.263492648@linuxfoundation.org> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220829105808.828227973@linuxfoundation.org> References: <20220829105808.828227973@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: David Hildenbrand commit 1d8d14641fd94a01b20a4abbf2749fd8eddcf57b upstream. If we ever get a write-fault on a write-protected page in a shared mapping, we'd be in trouble (again). Instead, we can simply map the page writable. And in fact, there is even a way right now to trigger that code via uffd-wp ever since we stared to support it for shmem in 5.19: -------------------------------------------------------------------------- #include #include #include #include #include #include #include #include #include #include #define HUGETLB_SIZE (2 * 1024 * 1024u) static char *map; int uffd; static int temp_setup_uffd(void) { struct uffdio_api uffdio_api; struct uffdio_register uffdio_register; struct uffdio_writeprotect uffd_writeprotect; struct uffdio_range uffd_range; uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY); if (uffd < 0) { fprintf(stderr, "syscall() failed: %d\n", errno); return -errno; } uffdio_api.api = UFFD_API; uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP; if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) { fprintf(stderr, "UFFDIO_API failed: %d\n", errno); return -errno; } if (!(uffdio_api.features & UFFD_FEATURE_PAGEFAULT_FLAG_WP)) { fprintf(stderr, "UFFD_FEATURE_WRITEPROTECT missing\n"); return -ENOSYS; } /* Register UFFD-WP */ uffdio_register.range.start = (unsigned long) map; uffdio_register.range.len = HUGETLB_SIZE; uffdio_register.mode = UFFDIO_REGISTER_MODE_WP; if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) < 0) { fprintf(stderr, "UFFDIO_REGISTER failed: %d\n", errno); return -errno; } /* Writeprotect a single page. */ uffd_writeprotect.range.start = (unsigned long) map; uffd_writeprotect.range.len = HUGETLB_SIZE; uffd_writeprotect.mode = UFFDIO_WRITEPROTECT_MODE_WP; if (ioctl(uffd, UFFDIO_WRITEPROTECT, &uffd_writeprotect)) { fprintf(stderr, "UFFDIO_WRITEPROTECT failed: %d\n", errno); return -errno; } /* Unregister UFFD-WP without prior writeunprotection. */ uffd_range.start = (unsigned long) map; uffd_range.len = HUGETLB_SIZE; if (ioctl(uffd, UFFDIO_UNREGISTER, &uffd_range)) { fprintf(stderr, "UFFDIO_UNREGISTER failed: %d\n", errno); return -errno; } return 0; } int main(int argc, char **argv) { int fd; fd = open("/dev/hugepages/tmp", O_RDWR | O_CREAT); if (!fd) { fprintf(stderr, "open() failed\n"); return -errno; } if (ftruncate(fd, HUGETLB_SIZE)) { fprintf(stderr, "ftruncate() failed\n"); return -errno; } map = mmap(NULL, HUGETLB_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (map == MAP_FAILED) { fprintf(stderr, "mmap() failed\n"); return -errno; } *map = 0; if (temp_setup_uffd()) return 1; *map = 0; return 0; } -------------------------------------------------------------------------- Above test fails with SIGBUS when there is only a single free hugetlb page. # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages # ./test Bus error (core dumped) And worse, with sufficient free hugetlb pages it will map an anonymous page into a shared mapping, for example, messing up accounting during unmap and breaking MAP_SHARED semantics: # echo 2 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages # ./test # cat /proc/meminfo | grep HugePages_ HugePages_Total: 2 HugePages_Free: 1 HugePages_Rsvd: 18446744073709551615 HugePages_Surp: 0 Reason is that uffd-wp doesn't clear the uffd-wp PTE bit when unregistering and consequently keeps the PTE writeprotected. Reason for this is to avoid the additional overhead when unregistering. Note that this is the case also for !hugetlb and that we will end up with writable PTEs that still have the uffd-wp PTE bit set once we return from hugetlb_wp(). I'm not touching the uffd-wp PTE bit for now, because it seems to be a generic thing -- wp_page_reuse() also doesn't clear it. VM_MAYSHARE handling in hugetlb_fault() for FAULT_FLAG_WRITE indicates that MAP_SHARED handling was at least envisioned, but could never have worked as expected. While at it, make sure that we never end up in hugetlb_wp() on write faults without VM_WRITE, because we don't support maybe_mkwrite() semantics as commonly used in the !hugetlb case -- for example, in wp_page_reuse(). Note that there is no need to do any kind of reservation in hugetlb_fault() in this case ... because we already have a hugetlb page mapped R/O that we will simply map writable and we are not dealing with COW/unsharing. Link: https://lkml.kernel.org/r/20220811103435.188481-3-david@redhat.com Fixes: b1f9e876862d ("mm/uffd: enable write protection for shmem & hugetlbfs") Signed-off-by: David Hildenbrand Reviewed-by: Mike Kravetz Cc: Bjorn Helgaas Cc: Cyrill Gorcunov Cc: Hugh Dickins Cc: Jamie Liu Cc: Kirill A. Shutemov Cc: Muchun Song Cc: Naoya Horiguchi Cc: Pavel Emelyanov Cc: Peter Feiner Cc: Peter Xu Cc: [5.19] Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/hugetlb.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5232,6 +5232,21 @@ static vm_fault_t hugetlb_wp(struct mm_s VM_BUG_ON(unshare && (flags & FOLL_WRITE)); VM_BUG_ON(!unshare && !(flags & FOLL_WRITE)); + /* + * hugetlb does not support FOLL_FORCE-style write faults that keep the + * PTE mapped R/O such as maybe_mkwrite() would do. + */ + if (WARN_ON_ONCE(!unshare && !(vma->vm_flags & VM_WRITE))) + return VM_FAULT_SIGSEGV; + + /* Let's take out MAP_SHARED mappings first. */ + if (vma->vm_flags & VM_MAYSHARE) { + if (unlikely(unshare)) + return 0; + set_huge_ptep_writable(vma, haddr, ptep); + return 0; + } + pte = huge_ptep_get(ptep); old_page = pte_page(pte); @@ -5766,12 +5781,11 @@ vm_fault_t hugetlb_fault(struct mm_struc * If we are going to COW/unshare the mapping later, we examine the * pending reservations for this page now. This will ensure that any * allocations necessary to record that reservation occur outside the - * spinlock. For private mappings, we also lookup the pagecache - * page now as it is used to determine if a reservation has been - * consumed. + * spinlock. Also lookup the pagecache page now as it is used to + * determine if a reservation has been consumed. */ if ((flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) && - !huge_pte_write(entry)) { + !(vma->vm_flags & VM_MAYSHARE) && !huge_pte_write(entry)) { if (vma_needs_reservation(h, vma, haddr) < 0) { ret = VM_FAULT_OOM; goto out_mutex; @@ -5779,9 +5793,7 @@ vm_fault_t hugetlb_fault(struct mm_struc /* Just decrements count, does not deallocate */ vma_end_reservation(h, vma, haddr); - if (!(vma->vm_flags & VM_MAYSHARE)) - pagecache_page = hugetlbfs_pagecache_page(h, - vma, haddr); + pagecache_page = hugetlbfs_pagecache_page(h, vma, haddr); } ptl = huge_pte_lock(h, mm, ptep);