path: root/sbin/dumpon
diff options
authorKonrad Witaszczyk <def@FreeBSD.org>2016-12-10 16:20:39 +0000
committerKonrad Witaszczyk <def@FreeBSD.org>2016-12-10 16:20:39 +0000
commit480f31c214725f732a6d0e8ef4cd7c56ff98e155 (patch)
tree3333be885c7a29334059f5a66c38dc0a367f3a7f /sbin/dumpon
parentaced69428c850b869d28355e41a0c4e7495fceaf (diff)
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
Notes: svn path=/head/; revision=309818
Diffstat (limited to 'sbin/dumpon')
3 files changed, 225 insertions, 12 deletions
diff --git a/sbin/dumpon/Makefile b/sbin/dumpon/Makefile
index 782117c16ff0..d0700ab16a89 100644
--- a/sbin/dumpon/Makefile
+++ b/sbin/dumpon/Makefile
@@ -1,7 +1,15 @@
# $FreeBSD$
+.include <src.opts.mk>
PROG= dumpon
+.if ${MK_OPENSSL} != "no"
+LIBADD= crypto
MAN= dumpon.8
.include <bsd.prog.mk>
diff --git a/sbin/dumpon/dumpon.8 b/sbin/dumpon/dumpon.8
index 81377124d803..14b0665ec1bb 100644
--- a/sbin/dumpon/dumpon.8
+++ b/sbin/dumpon/dumpon.8
@@ -28,7 +28,7 @@
.\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
-.Dd October 3, 2016
+.Dd December 10, 2016
@@ -37,6 +37,7 @@
.Op Fl v
+.Op Fl k Ar public_key_file
.Ar special_file
.Op Fl v
@@ -56,7 +57,9 @@ normally occur from the system multi-user initialization file
.Pa /etc/rc ,
controlled by the
.Dq dumpdev
-variable in the boot time configuration file
+.Dq dumppubkey
+variables in the boot time configuration file
.Pa /etc/rc.conf .
The default type of kernel crash dump is the mini crash dump.
@@ -82,6 +85,35 @@ total amount of physical memory as reported by the
+.Op Fl k Ar public_key_file
+flag causes
+to generate a one-time key for kernel crash dump encryption.
+The key will be replaced by a new one when the
+utility is run again.
+The key is encrypted using
+.Ar public_key_file .
+This process is sandboxed using
+.Xr capsicum 4 .
+Both plain and encrypted keys are sent to the kernel using
+.Xr ioctl 2 .
+A user can specify the
+.Ar public_key_file
+in the
+.Dq dumppubkey
+variable defined in
+.Pa /etc/rc.conf
+for use with the
+.Pa /etc/rc.d/dumpon
+.Xr rc 8
+This flag requires a kernel compiled with the
+kernel option.
.Fl l
flag causes
@@ -140,13 +172,95 @@ standard swap areas
.It Pa /etc/rc.conf
boot-time system configuration
+In order to generate an RSA private key a user can use the
+.Xr genrsa 1
+.Dl # openssl genrsa -out private.pem 4096
+A public key can be extracted from the private key using the
+.Xr rsa 1
+.Dl # openssl rsa -in private.pem -out public.pem -pubout
+Once the RSA keys are created the private key should be moved to a safe place.
+.Pa public.pem
+can be used by
+to configure encrypted kernel crash dumps:
+.Dl # dumpon -k public.pem /dev/ada0s1b
+It is recommended to test if the kernel saves encrypted crash dumps using the
+current configuration.
+The easiest way to do that is to cause a kernel panic using the
+.Xr ddb 4
+.Dl # sysctl debug.kdb.panic=1
+In the debugger the following commands should be typed to write a core dump and
+.Dl db> call doadump(0)
+.Dl db> reset
+After reboot
+.Xr savecore 8
+should be able to save the core dump in the core directory which is
+.Pa /var/crash
+by default:
+.Dl # savecore /var/crash /dev/ada0s1b
+Three files should be created in the core directory:
+.Pa info.# ,
+.Pa key.#
+.Pa vmcore_encrypted.#
+.Dq #
+is the number of the last core dump saved by
+.Xr savecore 8 .
+.Pa vmcore_encrypted.#
+can be decrypted using the
+.Xr decryptcore 8
+.Dl # decryptcore -p private.pem -k key.# -e vmcore_encrypted.# -c vmcore.#
+or shorter:
+.Dl # decryptcore -p private.pem -n #
+.Pa vmcore.#
+can be now examined using
+.Xr kgdb 1 :
+.Dl # kgdb /usr/obj/sys/GENERIC/kernel.debug vmcore.#
+or shorter:
+.Dl # kgdb -n # /usr/obj/sys/GENERIC/kernel.debug
+The core was decrypted properly if
+.Xr kgdb 1
+does not print any errors.
+.Xr kgdb 1 ,
+.Xr ddb 4 ,
.Xr fstab 5 ,
.Xr rc.conf 5 ,
.Xr config 8 ,
.Xr init 8 ,
.Xr loader 8 ,
.Xr rc 8 ,
+.Xr decryptcore 8 ,
.Xr savecore 8 ,
.Xr swapon 8 ,
.Xr panic 9
diff --git a/sbin/dumpon/dumpon.c b/sbin/dumpon/dumpon.c
index 8407111c7f65..a1d77c852a48 100644
--- a/sbin/dumpon/dumpon.c
+++ b/sbin/dumpon/dumpon.c
@@ -42,13 +42,16 @@ static char sccsid[] = "From: @(#)swapon.c 8.1 (Berkeley) 6/5/93";
#include <sys/param.h>
+#include <sys/capsicum.h>
#include <sys/disk.h>
#include <sys/sysctl.h>
+#include <assert.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
+#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
@@ -56,13 +59,19 @@ __FBSDID("$FreeBSD$");
#include <sysexits.h>
#include <unistd.h>
+#include <openssl/err.h>
+#include <openssl/pem.h>
+#include <openssl/rsa.h>
static int verbose;
static void
fprintf(stderr, "%s\n%s\n%s\n",
- "usage: dumpon [-v] special_file",
+ "usage: dumpon [-v] [-k public_key_file] special_file",
" dumpon [-v] off",
" dumpon [-v] -l");
@@ -94,6 +103,59 @@ check_size(int fd, const char *fn)
+static void
+genkey(const char *pubkeyfile, struct diocskerneldump_arg *kda)
+ FILE *fp;
+ RSA *pubkey;
+ assert(pubkeyfile != NULL);
+ assert(kda != NULL);
+ fp = NULL;
+ pubkey = NULL;
+ fp = fopen(pubkeyfile, "r");
+ if (fp == NULL)
+ err(1, "Unable to open %s", pubkeyfile);
+ if (cap_enter() < 0 && errno != ENOSYS)
+ err(1, "Unable to enter capability mode");
+ pubkey = RSA_new();
+ if (pubkey == NULL) {
+ errx(1, "Unable to allocate an RSA structure: %s",
+ ERR_error_string(ERR_get_error(), NULL));
+ }
+ pubkey = PEM_read_RSA_PUBKEY(fp, &pubkey, NULL, NULL);
+ fclose(fp);
+ fp = NULL;
+ if (pubkey == NULL)
+ errx(1, "Unable to read data from %s.", pubkeyfile);
+ kda->kda_encryptedkeysize = RSA_size(pubkey);
+ if (kda->kda_encryptedkeysize > KERNELDUMP_ENCKEY_MAX_SIZE) {
+ errx(1, "Public key has to be at most %db long.",
+ }
+ kda->kda_encryptedkey = calloc(1, kda->kda_encryptedkeysize);
+ if (kda->kda_encryptedkey == NULL)
+ err(1, "Unable to allocate encrypted key");
+ kda->kda_encryption = KERNELDUMP_ENC_AES_256_CBC;
+ arc4random_buf(kda->kda_key, sizeof(kda->kda_key));
+ if (RSA_public_encrypt(sizeof(kda->kda_key), kda->kda_key,
+ kda->kda_encryptedkey, pubkey,
+ RSA_PKCS1_PADDING) != (int)kda->kda_encryptedkeysize) {
+ errx(1, "Unable to encrypt the one-time key.");
+ }
+ RSA_free(pubkey);
static void
@@ -123,13 +185,20 @@ listdumpdev(void)
main(int argc, char *argv[])
+ struct diocskerneldump_arg kda;
+ const char *pubkeyfile;
int ch;
int i, fd;
- u_int u;
int do_listdumpdev = 0;
+ bool enable;
- while ((ch = getopt(argc, argv, "lv")) != -1)
+ pubkeyfile = NULL;
+ while ((ch = getopt(argc, argv, "k:lv")) != -1)
switch((char)ch) {
+ case 'k':
+ pubkeyfile = optarg;
+ break;
case 'l':
do_listdumpdev = 1;
@@ -151,7 +220,15 @@ main(int argc, char *argv[])
if (argc != 1)
- if (strcmp(argv[0], "off") != 0) {
+ enable = (strcmp(argv[0], "off") != 0);
+#ifndef HAVE_CRYPTO
+ if (pubkeyfile != NULL) {
+ enable = false;
+ warnx("Unable to use the public key. Recompile dumpon with OpenSSL support.");
+ }
+ if (enable) {
char tmp[PATH_MAX];
char *dumpdev;
@@ -171,18 +248,32 @@ main(int argc, char *argv[])
if (fd < 0)
err(EX_OSFILE, "%s", dumpdev);
check_size(fd, dumpdev);
- u = 0;
- i = ioctl(fd, DIOCSKERNELDUMP, &u);
- u = 1;
- i = ioctl(fd, DIOCSKERNELDUMP, &u);
+ bzero(&kda, sizeof(kda));
+ kda.kda_enable = 0;
+ i = ioctl(fd, DIOCSKERNELDUMP, &kda);
+ explicit_bzero(&kda, sizeof(kda));
+ if (pubkeyfile != NULL)
+ genkey(pubkeyfile, &kda);
+ kda.kda_enable = 1;
+ i = ioctl(fd, DIOCSKERNELDUMP, &kda);
+ explicit_bzero(kda.kda_encryptedkey, kda.kda_encryptedkeysize);
+ free(kda.kda_encryptedkey);
+ explicit_bzero(&kda, sizeof(kda));
if (i == 0 && verbose)
printf("kernel dumps on %s\n", dumpdev);
} else {
if (fd < 0)
- u = 0;
- i = ioctl(fd, DIOCSKERNELDUMP, &u);
+ kda.kda_enable = 0;
+ i = ioctl(fd, DIOCSKERNELDUMP, &kda);
+ explicit_bzero(&kda, sizeof(kda));
if (i == 0 && verbose)
printf("kernel dumps disabled\n");