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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>
This commit is contained in:
Bernd Schmidt 2010-05-25 23:43:00 -07:00 committed by Linus Torvalds
parent 0cae3457b1
commit 3c7b204547
1 changed files with 18 additions and 14 deletions
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32
mm/nommu.c
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@ -918,14 +918,6 @@ static int validate_mmap_request(struct file *file,
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 @@ static int validate_mmap_request(struct file *file,
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 @@ static unsigned long determine_vm_flags(struct file *file,
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