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authorDavid Hildenbrand <david@redhat.com>2023-01-02 19:08:55 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-01-19 04:12:57 +0300
commitb6b7a8faf05c709cd9f63d3b7d9c66bd91bc3b0d (patch)
treee9314f6d0ce7fd59966ee70989134666ed5b477a /mm/nommu.c
parentfc4f4be9b5271e43eeb4c675d190fa9734de9ea3 (diff)
downloadlinux-b6b7a8faf05c709cd9f63d3b7d9c66bd91bc3b0d.tar.xz
mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings
Let's stop using VM_MAYSHARE for MAP_PRIVATE mappings and use VM_MAYOVERLAY instead. Rewrite determine_vm_flags() to make the whole logic easier to digest, and to cleanly separate MAP_PRIVATE vs. MAP_SHARED. No functional change intended. Link: https://lkml.kernel.org/r/20230102160856.500584-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Cc: Arnd Bergmann <arnd@arndb.de> 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>
Diffstat (limited to 'mm/nommu.c')
-rw-r--r--mm/nommu.c51
1 files changed, 30 insertions, 21 deletions
diff --git a/mm/nommu.c b/mm/nommu.c
index 1671ebbecb8d..df1711acdf5b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -892,29 +892,36 @@ static unsigned long determine_vm_flags(struct file *file,
unsigned long vm_flags;
vm_flags = calc_vm_prot_bits(prot, 0) | calc_vm_flag_bits(flags);
- /* vm_flags |= mm->def_flags; */
- if (!(capabilities & NOMMU_MAP_DIRECT)) {
- /* attempt to share read-only copies of mapped file chunks */
+ if (!file) {
+ /*
+ * MAP_ANONYMOUS. MAP_SHARED is mapped to MAP_PRIVATE, because
+ * there is no fork().
+ */
vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
- if (file && !(prot & PROT_WRITE))
- vm_flags |= VM_MAYSHARE;
+ } else if (flags & MAP_PRIVATE) {
+ /* MAP_PRIVATE file mapping */
+ if (capabilities & NOMMU_MAP_DIRECT)
+ vm_flags |= (capabilities & NOMMU_VMFLAGS);
+ else
+ vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+
+ if (!(prot & PROT_WRITE) && !current->ptrace)
+ /*
+ * R/O private file mapping which cannot be used to
+ * modify memory, especially also not via active ptrace
+ * (e.g., set breakpoints) or later by upgrading
+ * permissions (no mprotect()). We can try overlaying
+ * the file mapping, which will work e.g., on chardevs,
+ * ramfs/tmpfs/shmfs and romfs/cramf.
+ */
+ vm_flags |= VM_MAYOVERLAY;
} else {
- /* overlay a shareable mapping on the backing device or inode
- * if possible - used for chardevs, ramfs/tmpfs/shmfs and
- * romfs/cramfs */
- vm_flags |= VM_MAYSHARE | (capabilities & NOMMU_VMFLAGS);
- if (flags & MAP_SHARED)
- vm_flags |= VM_SHARED;
+ /* MAP_SHARED file mapping: NOMMU_MAP_DIRECT is set. */
+ vm_flags |= VM_SHARED | VM_MAYSHARE |
+ (capabilities & NOMMU_VMFLAGS);
}
- /* refuse to let anyone share private mappings with this process if
- * it's being traced - otherwise breakpoints set in it may interfere
- * with another untraced process
- */
- if ((flags & MAP_PRIVATE) && current->ptrace)
- vm_flags &= ~VM_MAYSHARE;
-
return vm_flags;
}
@@ -952,9 +959,11 @@ static int do_mmap_private(struct vm_area_struct *vma,
void *base;
int ret, order;
- /* invoke the file's mapping function so that it can keep track of
- * shared mappings on devices or memory
- * - VM_MAYSHARE will be set if it may attempt to share
+ /*
+ * Invoke the file's mapping function so that it can keep track of
+ * shared mappings on devices or memory. VM_MAYOVERLAY will be set if
+ * it may attempt to share, which will make is_nommu_shared_mapping()
+ * happy.
*/
if (capabilities & NOMMU_MAP_DIRECT) {
ret = call_mmap(vma->vm_file, vma);