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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: MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9F60B4000A X-Stat-Signature: qg8c193yix7uf5xusa4jdqzurfdkzc5z X-HE-Tag: 1696711871-460677 X-HE-Meta: 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 bCcQD/j+ 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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 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);