On Dec 10, 2016, at 10:20 AM, Konrad Witaszczyk wrote:
Author: def
Date: Sat Dec 10 16:20:39 2016
New Revision: 309818
URL: https://svnweb.freebsd.org/changeset/base/309818
Log:
Add support for encrypted kernel crash dumps.
Changes include modifications in kernel crash dump routines,
dumpon(8) and
savecore(8). A new tool called decryptcore(8) was added.
A new DIOCSKERNELDUMP I/O control was added to send a kernel crash
dump
configuration in the diocskerneldump_arg structure to the kernel.
The old DIOCSKERNELDUMP I/O control was renamed to
DIOCSKERNELDUMP_FREEBSD11 for
backward ABI compatibility.
dumpon(8) generates an one-time random symmetric key and encrypts
it using
an RSA public key in capability mode. Currently only AES-256-CBC is
supported
but EKCD was designed to implement support for other algorithms in
the future.
The public key is chosen using the -k flag. The dumpon rc(8) script
can do this
automatically during startup using the dumppubkey rc.conf(5)
variable. Once the
keys are calculated dumpon sends them to the kernel via
DIOCSKERNELDUMP I/O
control.
When the kernel receives the DIOCSKERNELDUMP I/O control it
generates a random
IV and sets up the key schedule for the specified algorithm. Each
time the
kernel tries to write a crash dump to the dump device, the IV is
replaced by
a SHA-256 hash of the previous value. This is intended to make a
possible
differential cryptanalysis harder since it is possible to write
multiple crash
dumps without reboot by repeating the following commands:
# sysctl debug.kdb.enter=1
db> call doadump(0)
db> continue
# savecore
A kernel dump key consists of an algorithm identifier, an IV and an
encrypted
symmetric key. The kernel dump key size is included in a kernel
dump header.
The size is an unsigned 32-bit integer and it is aligned to a block
size.
The header structure has 512 bytes to match the block size so it
was required to
make a panic string 4 bytes shorter to add a new field to the
header structure.
If the kernel dump key size in the header is nonzero it is assumed
that the
kernel dump key is placed after the first header on the dump device
and the core
dump is encrypted.
Separate functions were implemented to write the kernel dump header
and the
kernel dump key as they need to be unencrypted. The dump_write
function encrypts
data if the kernel was compiled with the EKCD option. Encrypted
kernel textdumps
are not supported due to the way they are constructed which makes
it impossible
to use the CBC mode for encryption. It should be also noted that
textdumps don't
contain sensitive data by design as a user decides what information
should be
dumped.
savecore(8) writes the kernel dump key to a key.# file if its size
in the header
is nonzero. # is the number of the current core dump.
decryptcore(8) decrypts the core dump using a private RSA key and
the kernel
dump key. This is performed by a child process in capability mode.
If the decryption was not successful the parent process removes a
partially
decrypted core dump.
Description on how to encrypt crash dumps was added to the
decryptcore(8),
dumpon(8), rc.conf(5) and savecore(8) manual pages.
EKCD was tested on amd64 using bhyve and i386, mipsel and sparc64
using QEMU.
The feature still has to be tested on arm and arm64 as it wasn't
possible to run
FreeBSD due to the problems with QEMU emulation and lack of hardware.
Designed by: def, pjd
Reviewed by: cem, oshogbo, pjd
Partial review: delphij, emaste, jhb, kib
Approved by: pjd (mentor)
Differential Revision: https://reviews.freebsd.org/D4712
Added:
head/sbin/decryptcore/
head/sbin/decryptcore/Makefile (contents, props changed)
head/sbin/decryptcore/decryptcore.8 (contents, props changed)
head/sbin/decryptcore/decryptcore.c (contents, props changed)
Modified:
head/etc/defaults/rc.conf
head/etc/rc.d/dumpon
head/sbin/Makefile
head/sbin/dumpon/Makefile
head/sbin/dumpon/dumpon.8
head/sbin/dumpon/dumpon.c
head/sbin/savecore/savecore.8
head/sbin/savecore/savecore.c
head/share/man/man5/rc.conf.5
head/sys/amd64/amd64/minidump_machdep.c
head/sys/arm/arm/minidump_machdep.c
head/sys/arm64/arm64/minidump_machdep.c
head/sys/conf/NOTES
head/sys/conf/files
head/sys/conf/options
head/sys/ddb/db_textdump.c
head/sys/dev/null/null.c
head/sys/geom/geom_dev.c
head/sys/i386/i386/minidump_machdep.c
head/sys/kern/kern_dump.c
head/sys/kern/kern_shutdown.c
head/sys/mips/mips/minidump_machdep.c
head/sys/sparc64/sparc64/dump_machdep.c
head/sys/sys/conf.h
head/sys/sys/disk.h
head/sys/sys/kerneldump.h
Nice! Any reason you left out PowerPC from this list though?
- Justin
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