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Add a new kernel config option, MD_ROOT_READONLY, which forces on the

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MD_READONLY flag for the md device automatically instantiated during
kernel init for an mdroot filesystem.

Note that there is specifically and by design no tunable or sysctl
control over this feature.  Without this option, you already have control
over whether the mdroot fs is writeable using vfs.root.mountfrom.options
from loader(8), the root_rw_mount rcvar, and by using "mount -u[rw] /"
or equivelent on the fly.  This option is being added to provide a way
to make the mdroot fs truly immutable before userland code begins running.

Differential Revision:	https://reviews.freebsd.org/D13411
This commit is contained in:
Ian Lepore 2017-12-20 18:23:22 +00:00
parent c19c7afee3
commit 5cf10fb96a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=327032
4 changed files with 15 additions and 4 deletions
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5
share/man/man4/md.4
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@ -7,7 +7,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd November 5, 2017
.Dd December 7, 2017
.Dt MD 4
.Os
.Sh NAME
@ -79,7 +79,8 @@ To create a kernel with a ramdisk or MD file system, your kernel config
needs the following options:
.Bd -literal -offset indent
options MD_ROOT # MD is a potential root device
options MD_ROOT_SIZE=8192 # 8MB ram disk
options MD_ROOT_READONLY # disallow mounting root writeable
options MD_ROOT_SIZE=8192 # 8MB ram disk
makeoptions MFS_IMAGE=/h/foo/ARM-MD
options ROOTDEVNAME=\\"ufs:md0\\"
.Ed

3
sys/conf/NOTES
View File

@ -1101,6 +1101,9 @@ options MD_ROOT_SIZE=10
# images of type mfs_root or md_root.
options MD_ROOT
# Write-protect the md root device so that it may not be mounted writeable.
options MD_ROOT_READONLY
# Disk quotas are supported when this option is enabled.
options QUOTA #enable disk quotas

1
sys/conf/options
View File

@ -165,6 +165,7 @@ MAC_STUB opt_dontuse.h
MAC_TEST opt_dontuse.h
MD_ROOT opt_md.h
MD_ROOT_FSTYPE opt_md.h
MD_ROOT_READONLY opt_md.h
MD_ROOT_SIZE opt_md.h
MFI_DEBUG opt_mfi.h
MFI_DECODE_LOG opt_mfi.h

10
sys/dev/md/md.c
View File

@ -1791,9 +1791,15 @@ md_preloaded(u_char *image, size_t length, const char *name)
sc->start = mdstart_preload;
if (name != NULL)
strlcpy(sc->file, name, sizeof(sc->file));
#if defined(MD_ROOT) && !defined(ROOTDEVNAME)
if (sc->unit == 0)
#ifdef MD_ROOT
if (sc->unit == 0) {
#ifndef ROOTDEVNAME
rootdevnames[0] = MD_ROOT_FSTYPE ":/dev/md0";
#endif
#ifdef MD_ROOT_READONLY
sc->flags |= MD_READONLY;
#endif
}
#endif
mdinit(sc);
if (name != NULL) {