svn commit: r309818 - in head: etc/defaults etc/rc.d sbin sbin/decryptcore sbin/dumpon sbin/savecore share/man/man5 sys/amd64/amd64 sys/arm/arm sys/arm64/arm64 sys/conf sys/ddb sys/dev/null sys/geo...

Sat Dec 10 20:53:53 UTC 2016

On 12/10/2016 20:20, Justin Hibbits wrote:
> 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?

The architectures that I listed implement separate minidump functions in their
MD code. I had to change them to implement EKCD. ppc and pc98 are not the case
and we don't have minidumps in riscv yet. It means that EKCD should also work on
ppc.
Of course all architectures supported by FreeBSD should be verified. However it
is mandatory to test all changes in MD code.

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