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[86.156.84.164]) by smtp.googlemail.com with ESMTPSA id u17-20020a05600c19d100b003dd1bd0b915sm20731309wmq.22.2023.04.03.15.28.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Apr 2023 15:28:41 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Andy Lutomirski , Lorenzo Stoakes Subject: [RFC PATCH 1/3] mm: drop the assumption that VM_SHARED always implies writable Date: Mon, 3 Apr 2023 23:28:30 +0100 Message-Id: <691c33e2fe8fc0fd879374739b50af48524175a3.1680560277.git.lstoakes@gmail.com> X-Mailer: git-send-email 2.40.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6839B4000C X-Stat-Signature: 8mzg5zbfnmdzgbgrrpfpf89xsuqwj3an X-HE-Tag: 1680560924-813123 X-HE-Meta: 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 /yZYLi8S 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 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: There are places in the kernel where there is an implicit assumption that VM_SHARED VMAs must either be writable or might become writable via e.g. mprotect(). We can explicitly check for the writable, shared case while remaining conservative - If VM_MAYWRITE is not set then, by definition, the memory can never be written to. Update these checks to also check for VM_MAYWRITE. 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 c85916e9f7db..373e1edd719c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -410,7 +410,7 @@ 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. @@ -513,7 +513,7 @@ 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 898ece0a3802..8e64041b1703 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -862,6 +862,17 @@ 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 2066a57786a8..58f257d60fee 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 a34abfe8c654..4d896515032c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3607,7 +3607,7 @@ 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 340125d08c03..606c395c4ddd 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -981,7 +981,7 @@ 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 51cd747884e3..c96dcce90772 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -106,7 +106,7 @@ 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); @@ -427,7 +427,7 @@ 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); @@ -2596,7 +2596,7 @@ 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; @@ -2671,7 +2671,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma_iter_store(&vmi, vma); mm->map_count++; if (vma->vm_file) { - 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); @@ -2688,7 +2688,7 @@ 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; expanded: @@ -2734,7 +2734,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, unmap_region(mm, &mm->mm_mt, vma, prev, next, vma->vm_start, 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); -- 2.40.0