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Sun, 30 Apr 2023 15:26:42 -0700 (PDT) Received: from lucifer.home ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.googlemail.com with ESMTPSA id g2-20020a5d5402000000b002da75c5e143sm26699865wrv.29.2023.04.30.15.26.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Apr 2023 15:26:41 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Matthew Wilcox , Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Andy Lutomirski , linux-fsdevel@vger.kernel.org, Jan Kara , Hugh Dickins , Lorenzo Stoakes Subject: [PATCH v2 1/3] mm: drop the assumption that VM_SHARED always implies writable Date: Sun, 30 Apr 2023 23:26:05 +0100 Message-Id: X-Mailer: git-send-email 2.40.1 In-Reply-To: References: MIME-Version: 1.0 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 10A3BC0009 X-Rspam-User: X-Stat-Signature: 6w3oh6mp46bnjtb7agkqpfxfupqud5x7 X-HE-Tag: 1682893603-6820 X-HE-Meta: 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 +5xoiq51 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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 67495ef79bb2..874fe0e38e65 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -413,7 +413,7 @@ 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. @@ -516,7 +516,7 @@ 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 27ce77080c79..3e8fb4601520 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -851,6 +851,17 @@ 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 4342200d5e2b..7ebd6229219a 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 b5ffbaf616f5..5eb59854e285 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -969,7 +969,7 @@ 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 5522130ae606..646e34e95a37 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); @@ -428,7 +428,7 @@ 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); @@ -2642,7 +2642,7 @@ 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; @@ -2717,7 +2717,7 @@ 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); @@ -2734,7 +2734,7 @@ 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); @@ -2781,7 +2781,7 @@ 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);