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authorDavid Hildenbrand2023-01-02 17:08:54 +0100
committerAndrew Morton2023-01-18 17:12:56 -0800
commitfc4f4be9b5271e43eeb4c675d190fa9734de9ea3 (patch)
treefbdc88b711df8a850345a8539784b29e84d7c920
parentda0618c146ca0e1412173a8a229dd737a73b1a4f (diff)
mm/nommu: factor out check for NOMMU shared mappings into is_nommu_shared_mapping()
Patch series "mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings". Trying to reduce the confusion around VM_SHARED and VM_MAYSHARE first requires !CONFIG_MMU to stop using VM_MAYSHARE for MAP_PRIVATE mappings. CONFIG_MMU only sets VM_MAYSHARE for MAP_SHARED mappings. This paves the way for further VM_MAYSHARE and VM_SHARED cleanups: for example, renaming VM_MAYSHARED to VM_MAP_SHARED to make it cleaner what is actually means. Let's first get the weird case out of the way and not use VM_MAYSHARE in MAP_PRIVATE mappings, using a new VM_MAYOVERLAY flag instead. This patch (of 3): We want to stop using VM_MAYSHARE in private mappings to pave the way for clarifying the semantics of VM_MAYSHARE vs. VM_SHARED and reduce the confusion. While CONFIG_MMU uses VM_MAYSHARE to represent MAP_SHARED, !CONFIG_MMU also sets VM_MAYSHARE for selected R/O private file mappings that are an effective overlay of a file mapping. Let's factor out all relevant VM_MAYSHARE checks in !CONFIG_MMU code into is_nommu_shared_mapping() first. Note that whenever VM_SHARED is set, VM_MAYSHARE must be set as well (unless there is a serious BUG). So there is not need to test for VM_SHARED manually. No functional change intended. Link: https://lkml.kernel.org/r/20230102160856.500584-1-david@redhat.com Link: https://lkml.kernel.org/r/20230102160856.500584-2-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: David Hildenbrand <david@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicolas Pitre <nico@fluxnic.net> Cc: Pavel Begunkov <asml.silence@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r--drivers/char/mem.c2
-rw-r--r--fs/cramfs/inode.c2
-rw-r--r--fs/proc/task_nommu.c2
-rw-r--r--fs/ramfs/file-nommu.c2
-rw-r--r--fs/romfs/mmap-nommu.c2
-rw-r--r--include/linux/mm.h15
-rw-r--r--io_uring/io_uring.c2
-rw-r--r--mm/nommu.c11
8 files changed, 27 insertions, 11 deletions
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 83bf2a4dcb57..ffb101d349f0 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -343,7 +343,7 @@ static unsigned zero_mmap_capabilities(struct file *file)
/* can't do an in-place private mapping if there's no MMU */
static inline int private_mapping_ok(struct vm_area_struct *vma)
{
- return vma->vm_flags & VM_MAYSHARE;
+ return is_nommu_shared_mapping(vma->vm_flags);
}
#else
diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 61ccf7722fc3..50e4e060db68 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -437,7 +437,7 @@ bailout:
static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma)
{
- return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
+ return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS;
}
static unsigned long cramfs_physmem_get_unmapped_area(struct file *file,
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 2fd06f52b6a4..0ec35072a8e5 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -38,7 +38,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
}
if (atomic_read(&mm->mm_count) > 1 ||
- vma->vm_flags & VM_MAYSHARE) {
+ is_nommu_shared_mapping(vma->vm_flags)) {
sbytes += size;
} else {
bytes += size;
diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index cb240eac5036..cd4537692751 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -264,7 +264,7 @@ out:
*/
static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
{
- if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
+ if (!is_nommu_shared_mapping(vma->vm_flags))
return -ENOSYS;
file_accessed(file);
diff --git a/fs/romfs/mmap-nommu.c b/fs/romfs/mmap-nommu.c
index 2c4a23113fb5..4578dc45e50a 100644
--- a/fs/romfs/mmap-nommu.c
+++ b/fs/romfs/mmap-nommu.c
@@ -63,7 +63,7 @@ static unsigned long romfs_get_unmapped_area(struct file *file,
*/
static int romfs_mmap(struct file *file, struct vm_area_struct *vma)
{
- return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
+ return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS;
}
static unsigned romfs_mmap_capabilities(struct file *file)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index eb5bfc77c2c2..791bac40bf8e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1347,6 +1347,21 @@ static inline bool is_cow_mapping(vm_flags_t flags)
return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
}
+#ifndef CONFIG_MMU
+static inline bool is_nommu_shared_mapping(vm_flags_t flags)
+{
+ /*
+ * NOMMU shared mappings are ordinary MAP_SHARED mappings and selected
+ * R/O MAP_PRIVATE file mappings that are an effective R/O overlay of
+ * a file mapping. R/O MAP_PRIVATE mappings might still modify
+ * underlying memory if ptrace is active, so this is only possible if
+ * ptrace does not apply. Note that there is no mprotect() to upgrade
+ * write permissions later.
+ */
+ return flags & VM_MAYSHARE;
+}
+#endif
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 2ac1cd8d23ea..3a934f733136 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3206,7 +3206,7 @@ static __cold int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
{
- return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -EINVAL;
+ return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -EINVAL;
}
static unsigned int io_uring_nommu_mmap_capabilities(struct file *file)
diff --git a/mm/nommu.c b/mm/nommu.c
index 5b83938ecb67..1671ebbecb8d 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -958,9 +958,10 @@ static int do_mmap_private(struct vm_area_struct *vma,
*/
if (capabilities & NOMMU_MAP_DIRECT) {
ret = call_mmap(vma->vm_file, vma);
+ /* shouldn't return success if we're not sharing */
+ if (WARN_ON_ONCE(!is_nommu_shared_mapping(vma->vm_flags)))
+ ret = -ENOSYS;
if (ret == 0) {
- /* shouldn't return success if we're not sharing */
- BUG_ON(!(vma->vm_flags & VM_MAYSHARE));
vma->vm_region->vm_top = vma->vm_region->vm_end;
return 0;
}
@@ -1106,7 +1107,7 @@ unsigned long do_mmap(struct file *file,
* these cases, sharing is handled in the driver or filesystem rather
* than here
*/
- if (vm_flags & VM_MAYSHARE) {
+ if (is_nommu_shared_mapping(vm_flags)) {
struct vm_region *pregion;
unsigned long pglen, rpglen, pgend, rpgend, start;
@@ -1116,7 +1117,7 @@ unsigned long do_mmap(struct file *file,
for (rb = rb_first(&nommu_region_tree); rb; rb = rb_next(rb)) {
pregion = rb_entry(rb, struct vm_region, vm_rb);
- if (!(pregion->vm_flags & VM_MAYSHARE))
+ if (!is_nommu_shared_mapping(pregion->vm_flags))
continue;
/* search for overlapping mappings on the same file */
@@ -1600,7 +1601,7 @@ static unsigned long do_mremap(unsigned long addr,
if (vma->vm_end != vma->vm_start + old_len)
return (unsigned long) -EFAULT;
- if (vma->vm_flags & VM_MAYSHARE)
+ if (is_nommu_shared_mapping(vma->vm_flags))
return (unsigned long) -EPERM;
if (new_len > vma->vm_region->vm_end - vma->vm_region->vm_start)