nommu: allow private mappings of read-only devices
Slightly rearrange the logic that determines capabilities and vm_flags.
Disable BDI_CAP_MAP_DIRECT in all cases if the device can't support the
protections. Allow private readonly mappings of readonly backing devices.
Signed-off-by: Bernd Schmidt <bernds_cb1@t-online.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: David McCullough <davidm@snapgear.com>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/nommu.c b/mm/nommu.c
index 63fa17d..b76f3ee 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -918,14 +918,6 @@
if (!(capabilities & BDI_CAP_MAP_DIRECT))
return -ENODEV;
- if (((prot & PROT_READ) && !(capabilities & BDI_CAP_READ_MAP)) ||
- ((prot & PROT_WRITE) && !(capabilities & BDI_CAP_WRITE_MAP)) ||
- ((prot & PROT_EXEC) && !(capabilities & BDI_CAP_EXEC_MAP))
- ) {
- printk("MAP_SHARED not completely supported on !MMU\n");
- return -EINVAL;
- }
-
/* we mustn't privatise shared mappings */
capabilities &= ~BDI_CAP_MAP_COPY;
}
@@ -941,6 +933,20 @@
capabilities &= ~BDI_CAP_MAP_DIRECT;
}
+ if (capabilities & BDI_CAP_MAP_DIRECT) {
+ if (((prot & PROT_READ) && !(capabilities & BDI_CAP_READ_MAP)) ||
+ ((prot & PROT_WRITE) && !(capabilities & BDI_CAP_WRITE_MAP)) ||
+ ((prot & PROT_EXEC) && !(capabilities & BDI_CAP_EXEC_MAP))
+ ) {
+ capabilities &= ~BDI_CAP_MAP_DIRECT;
+ if (flags & MAP_SHARED) {
+ printk(KERN_WARNING
+ "MAP_SHARED not completely supported on !MMU\n");
+ return -EINVAL;
+ }
+ }
+ }
+
/* handle executable mappings and implied executable
* mappings */
if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
@@ -996,22 +1002,20 @@
unsigned long vm_flags;
vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags);
- vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
/* vm_flags |= mm->def_flags; */
if (!(capabilities & BDI_CAP_MAP_DIRECT)) {
/* attempt to share read-only copies of mapped file chunks */
+ vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
if (file && !(prot & PROT_WRITE))
vm_flags |= VM_MAYSHARE;
- }
- else {
+ } 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 & BDI_CAP_VMFLAGS);
if (flags & MAP_SHARED)
- vm_flags |= VM_MAYSHARE | VM_SHARED;
- else if ((((vm_flags & capabilities) ^ vm_flags) & BDI_CAP_VMFLAGS) == 0)
- vm_flags |= VM_MAYSHARE;
+ vm_flags |= VM_SHARED;
}
/* refuse to let anyone share private mappings with this process if