From patchwork Sat Oct 7 20:50:59 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lorenzo Stoakes X-Patchwork-Id: 13412488 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 353FD30FB1 for ; Sat, 7 Oct 2023 20:51:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Ru+OOEp9" Received: from mail-wr1-x431.google.com (mail-wr1-x431.google.com [IPv6:2a00:1450:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7761095; Sat, 7 Oct 2023 13:51:11 -0700 (PDT) Received: by mail-wr1-x431.google.com with SMTP id ffacd0b85a97d-3248aa5cf4eso3225180f8f.1; Sat, 07 Oct 2023 13:51:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1696711870; x=1697316670; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=3Eqt+lFhGqyhgA/GIcCG4Sd1WLEsHw06nfkpMalVsW4=; b=Ru+OOEp90ZxWbfQzr2tymGylhyaTuLX2Eu0LjuozDBlltxaJqqvME9fPpc7GmyWXIi nFSXmB3DnPT/ZAjVg9pYowUpeR3FPny4d+MvP5z5OIRtUPfb3ymIInbNhvtMziT4c9iG xqDz7LGy+G/zsROsLfur+ukqskhSW83xPPbdC4bYnVYO+MIhB+67RO7CTggMmRAjVFRJ /IubIvMIuh/un2lP28NBpQnVAuHeN05slSna+7GJLjQT9qXJa6fzXVw+iniY2W5ri8bD EzuLvYlH08S/STbXb1VWcxsWlFXBAKcn/03JnsxgTzea46TDRezVTTU2EIlFl6gX8k5R dWZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696711870; x=1697316670; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=3Eqt+lFhGqyhgA/GIcCG4Sd1WLEsHw06nfkpMalVsW4=; b=rylqF+l5ao+etdiSPKBMd6oEIKzWGXmDwK6UZ+7vcg4Dz8xt8XvL6eh/Ju0ICPGSgz vHO7Oyre/ArhcH2qglvDmhZw7/C2NTRJueBzxadzghbPnNChRWZiSnTGAkHa3Ygg7vp1 FYPYCcgy4tN9r39o79HAp7vgfYHoj3yU53oUW5b4LsvXOhWlg3IvK555mVD/ZB3EMSsg 7i+tj6pd5DvxjO1VA8ZcQGFJMn0E1eP+5EIyH59BsQULYkdNs89BKlHU70EprtogcSzy YlX0OFPZKyV8sIr9FijiTYnsJBvRAixVIKCRh0u02uoV3z2OX/zwz7indx/OS4Klnf6G kcLQ== X-Gm-Message-State: AOJu0YwJvIerH44n6Q2S/TPUyRHDpiiwzbAimg0ewzH/gbw5gje5GgeZ 8eiVwcPzW9oXqWLvGD/1ogg= X-Google-Smtp-Source: AGHT+IGDGw56aAVS4Ps+h8icv4jAQgm4Hk3HtBxKyknFOFfb//OHVHdrVHz4nilvcQwrSS5yFdaaXw== X-Received: by 2002:a5d:4c8a:0:b0:313:ecd3:7167 with SMTP id z10-20020a5d4c8a000000b00313ecd37167mr9918903wrs.42.1696711869667; Sat, 07 Oct 2023 13:51:09 -0700 (PDT) Received: from lucifer.home ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.googlemail.com with ESMTPSA id g7-20020adfe407000000b003232d122dbfsm5120550wrm.66.2023.10.07.13.51.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Oct 2023 13:51:08 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Matthew Wilcox , Hugh Dickins , Andy Lutomirski , Jan Kara , linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, Lorenzo Stoakes Subject: [PATCH v3 1/3] mm: drop the assumption that VM_SHARED always implies writable Date: Sat, 7 Oct 2023 21:50:59 +0100 Message-ID: X-Mailer: git-send-email 2.42.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net There is a general assumption that VMAs with the VM_SHARED flag set are writable. If the VM_MAYWRITE flag is not set, then this is simply not the case. Update those checks which affect the struct address_space->i_mmap_writable field to explicitly test for this by introducing [vma_]is_shared_maywrite() helper functions. This remains entirely conservative, as the lack of VM_MAYWRITE guarantees that the VMA cannot be written to. Suggested-by: Andy Lutomirski Signed-off-by: Lorenzo Stoakes --- include/linux/fs.h | 4 ++-- include/linux/mm.h | 11 +++++++++++ kernel/fork.c | 2 +- mm/filemap.c | 2 +- mm/madvise.c | 2 +- mm/mmap.c | 12 ++++++------ 6 files changed, 22 insertions(+), 11 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 92a9c6157de1..e9c03fb00d5c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -454,7 +454,7 @@ extern const struct address_space_operations empty_aops; * It is also used to block modification of page cache contents through * memory mappings. * @gfp_mask: Memory allocation flags to use for allocating pages. - * @i_mmap_writable: Number of VM_SHARED mappings. + * @i_mmap_writable: Number of VM_SHARED, VM_MAYWRITE mappings. * @nr_thps: Number of THPs in the pagecache (non-shmem only). * @i_mmap: Tree of private and shared mappings. * @i_mmap_rwsem: Protects @i_mmap and @i_mmap_writable. @@ -557,7 +557,7 @@ static inline int mapping_mapped(struct address_space *mapping) /* * Might pages of this file have been modified in userspace? - * Note that i_mmap_writable counts all VM_SHARED vmas: do_mmap + * Note that i_mmap_writable counts all VM_SHARED, VM_MAYWRITE vmas: do_mmap * marks vma as VM_SHARED if it is shared, and the file was opened for * writing i.e. vma may be mprotected writable even if now readonly. * diff --git a/include/linux/mm.h b/include/linux/mm.h index a7b667786cde..c9e9628addc4 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -937,6 +937,17 @@ static inline bool vma_is_accessible(struct vm_area_struct *vma) return vma->vm_flags & VM_ACCESS_FLAGS; } +static inline bool is_shared_maywrite(vm_flags_t vm_flags) +{ + return (vm_flags & (VM_SHARED | VM_MAYWRITE)) == + (VM_SHARED | VM_MAYWRITE); +} + +static inline bool vma_is_shared_maywrite(struct vm_area_struct *vma) +{ + return is_shared_maywrite(vma->vm_flags); +} + static inline struct vm_area_struct *vma_find(struct vma_iterator *vmi, unsigned long max) { diff --git a/kernel/fork.c b/kernel/fork.c index e45a4457ba83..1e6c656e0857 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -733,7 +733,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, get_file(file); i_mmap_lock_write(mapping); - if (tmp->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(tmp)) mapping_allow_writable(mapping); flush_dcache_mmap_lock(mapping); /* insert tmp into the share list, just after mpnt */ diff --git a/mm/filemap.c b/mm/filemap.c index 48cd16c54e86..ad559f94e125 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3637,7 +3637,7 @@ int generic_file_mmap(struct file *file, struct vm_area_struct *vma) */ int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma) { - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) + if (vma_is_shared_maywrite(vma)) return -EINVAL; return generic_file_mmap(file, vma); } diff --git a/mm/madvise.c b/mm/madvise.c index a4a20de50494..5c74fb645de8 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -999,7 +999,7 @@ static long madvise_remove(struct vm_area_struct *vma, return -EINVAL; } - if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE)) + if (!vma_is_shared_maywrite(vma)) return -EACCES; offset = (loff_t)(start - vma->vm_start) diff --git a/mm/mmap.c b/mm/mmap.c index 673429ee8a9e..6f6856b3267a 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -107,7 +107,7 @@ void vma_set_page_prot(struct vm_area_struct *vma) static void __remove_shared_vm_struct(struct vm_area_struct *vma, struct file *file, struct address_space *mapping) { - if (vma->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(vma)) mapping_unmap_writable(mapping); flush_dcache_mmap_lock(mapping); @@ -384,7 +384,7 @@ static unsigned long count_vma_pages_range(struct mm_struct *mm, static void __vma_link_file(struct vm_area_struct *vma, struct address_space *mapping) { - if (vma->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(vma)) mapping_allow_writable(mapping); flush_dcache_mmap_lock(mapping); @@ -2767,7 +2767,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma->vm_pgoff = pgoff; if (file) { - if (vm_flags & VM_SHARED) { + if (is_shared_maywrite(vm_flags)) { error = mapping_map_writable(file->f_mapping); if (error) goto free_vma; @@ -2842,7 +2842,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, mm->map_count++; if (vma->vm_file) { i_mmap_lock_write(vma->vm_file->f_mapping); - if (vma->vm_flags & VM_SHARED) + if (vma_is_shared_maywrite(vma)) mapping_allow_writable(vma->vm_file->f_mapping); flush_dcache_mmap_lock(vma->vm_file->f_mapping); @@ -2859,7 +2859,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, /* Once vma denies write, undo our temporary denial count */ unmap_writable: - if (file && vm_flags & VM_SHARED) + if (file && is_shared_maywrite(vm_flags)) mapping_unmap_writable(file->f_mapping); file = vma->vm_file; ksm_add_vma(vma); @@ -2907,7 +2907,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start, vma->vm_end, vma->vm_end, true); } - if (file && (vm_flags & VM_SHARED)) + if (file && is_shared_maywrite(vm_flags)) mapping_unmap_writable(file->f_mapping); free_vma: vm_area_free(vma);