Commit 3c7b2045 authored by Bernd Schmidt's avatar Bernd Schmidt Committed by Linus Torvalds
Browse files

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: default avatarBernd Schmidt <bernds_cb1@t-online.de>
Signed-off-by: default avatarMike Frysinger <vapier@gentoo.org>
Acked-by: default avatarDavid McCullough <davidm@snapgear.com>
Acked-by: default avatarGreg Ungerer <gerg@uclinux.org>
Acked-by: default avatarPaul Mundt <lethal@linux-sh.org>
Acked-by: default avatarDavid Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0cae3457

mm/nommu.c

+18 −14
Original line number Diff line number Diff line
@@ -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

CRA Git | Maintained and supported by SUSTech CRA and CCSE