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Message-ID: <e1bcbcba7ffbe421bbd262029a3a59178b52e3c5.1696709413.git.lstoakes@gmail.com>
Date: Sat, 7 Oct 2023 21:50:59 +0100
From: Lorenzo Stoakes <lstoakes@...il.com>
To: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Kravetz <mike.kravetz@...cle.com>,
Muchun Song <muchun.song@...ux.dev>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Hugh Dickins <hughd@...gle.com>,
Andy Lutomirski <luto@...nel.org>, Jan Kara <jack@...e.cz>,
linux-fsdevel@...r.kernel.org, bpf@...r.kernel.org,
Lorenzo Stoakes <lstoakes@...il.com>
Subject: [PATCH v3 1/3] mm: drop the assumption that VM_SHARED always implies writable
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 <luto@...nel.org>
Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
---
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);
--
2.42.0
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