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SubjectRe: [RFC 1/1] Add dm verity root hash pkcs7 sig validation.
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On 5/21/19 7:54 AM, Jaskaran Khurana wrote:
> Adds in-kernel pkcs7 signature checking for the roothash of
> the dm-verity hash tree.
>
> The verification is to support cases where the roothash is not secured by
> Trusted Boot, UEFI Secureboot or similar technologies.
> One of the use cases for this is for dm-verity volumes mounted after boot,
> the root hash provided during the creation of the dm-verity volume has to
> be secure and thus in-kernel validation implemented here will be used
> before we trust the root hash and allow the block device to be created.
>
The first patch was your cover letter, I'd suggest name it that way in
the subject.

> The signature being provided for verification must verify the root hash and
> must be trusted by the builtin keyring for verification to succeed.
>
> Adds DM_VERITY_VERIFY_ROOTHASH_SIG: roothash verification
> against the roothash signature file *if* specified, if signature file is
> specified verification must succeed prior to creation of device mapper
> block device.
>
> Adds DM_VERITY_VERIFY_ROOTHASH_SIG_FORCE: roothash signature *must* be
> specified for all dm verity volumes and verification must succeed prior
> to creation of device mapper block device.
>
> Signed-off-by: Jaskaran Khurana <jaskarankhurana@linux.microsoft.com>
> ---
> drivers/md/Kconfig | 23 ++++++
> drivers/md/Makefile | 2 +-
> drivers/md/dm-verity-target.c | 44 ++++++++--
> drivers/md/dm-verity-verify-sig.c | 129 ++++++++++++++++++++++++++++++
> drivers/md/dm-verity-verify-sig.h | 32 ++++++++
> 5 files changed, 222 insertions(+), 8 deletions(-)
> create mode 100644 drivers/md/dm-verity-verify-sig.c
> create mode 100644 drivers/md/dm-verity-verify-sig.h
>
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index db269a348b20..da4115753f25 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -489,6 +489,29 @@ config DM_VERITY
>
> If unsure, say N.
>
> +config DM_VERITY_VERIFY_ROOTHASH_SIG
> + def_bool n
> + bool "Verity data device root hash signature verification support"
> + depends on DM_VERITY
> + select SYSTEM_DATA_VERIFICATION
> + help
> + The device mapper target created by DM-VERITY can be validated if the
> + pre-generated tree of cryptographic checksums passed has a pkcs#7
> + signature file that can validate the roothash of the tree.
> +
> + If unsure, say N.
> +
> +config DM_VERITY_VERIFY_ROOTHASH_SIG_FORCE
> + def_bool n
> + bool "Forces all dm verity data device root hash should be signed"
> + depends on DM_VERITY_VERIFY_ROOTHASH_SIG
> + help
> + The device mapper target created by DM-VERITY will succeed only if the
> + pre-generated tree of cryptographic checksums passed also has a pkcs#7
> + signature file that can validate the roothash of the tree.
> +
> + If unsure, say N.
> +
> config DM_VERITY_FEC
> bool "Verity forward error correction support"
> depends on DM_VERITY
> diff --git a/drivers/md/Makefile b/drivers/md/Makefile
> index be7a6eb92abc..8a8c142bcfe1 100644
> --- a/drivers/md/Makefile
> +++ b/drivers/md/Makefile
> @@ -61,7 +61,7 @@ obj-$(CONFIG_DM_LOG_USERSPACE) += dm-log-userspace.o
> obj-$(CONFIG_DM_ZERO) += dm-zero.o
> obj-$(CONFIG_DM_RAID) += dm-raid.o
> obj-$(CONFIG_DM_THIN_PROVISIONING) += dm-thin-pool.o
> -obj-$(CONFIG_DM_VERITY) += dm-verity.o
> +obj-$(CONFIG_DM_VERITY) += dm-verity.o dm-verity-verify-sig.o
> obj-$(CONFIG_DM_CACHE) += dm-cache.o
> obj-$(CONFIG_DM_CACHE_SMQ) += dm-cache-smq.o
> obj-$(CONFIG_DM_ERA) += dm-era.o
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index f4c31ffaa88e..53aebfa8bc38 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -16,7 +16,7 @@
>
> #include "dm-verity.h"
> #include "dm-verity-fec.h"
> -
> +#include "dm-verity-verify-sig.h"
> #include <linux/module.h>
> #include <linux/reboot.h>
>
> @@ -34,7 +34,11 @@
> #define DM_VERITY_OPT_IGN_ZEROES "ignore_zero_blocks"
> #define DM_VERITY_OPT_AT_MOST_ONCE "check_at_most_once"
>
> -#define DM_VERITY_OPTS_MAX (2 + DM_VERITY_OPTS_FEC)
> +#define DM_VERITY_OPTS_MAX (2 + DM_VERITY_OPTS_FEC + \
> + DM_VERITY_ROOT_HASH_VERIFICATION_OPTS)
> +
> +#define DM_VERITY_MANDATORY_ARGS 10
> +
>
> static unsigned dm_verity_prefetch_cluster = DM_VERITY_DEFAULT_PREFETCH_SIZE;
>
> @@ -855,7 +859,8 @@ static int verity_alloc_zero_digest(struct dm_verity *v)
> return r;
> }
>
> -static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v)
> +static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
> + struct dm_verity_sig_opts *verify_args)
> {
> int r;
> unsigned argc;
> @@ -904,6 +909,15 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v)
> if (r)
> return r;
> continue;
> + } else if (verity_verify_is_sig_opt_arg(arg_name)) {
> + r = verity_verify_sig_parse_opt_args(as, v,
> + verify_args,
> + &argc, arg_name);
> + if (r) {
> + ti->error = "Could not parse the sig args";
> + return r;
> + }
> + continue;
> }
>
> ti->error = "Unrecognized verity feature request";
> @@ -930,6 +944,7 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v)
> static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> {
> struct dm_verity *v;
> + struct dm_verity_sig_opts verify_args = {0};
> struct dm_arg_set as;
> unsigned int num;
> unsigned long long num_ll;
> @@ -937,6 +952,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> int i;
> sector_t hash_position;
> char dummy;
> + char *root_hash_digest_to_validate = NULL;
>
> v = kzalloc(sizeof(struct dm_verity), GFP_KERNEL);
> if (!v) {
> @@ -956,7 +972,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> goto bad;
> }
>
> - if (argc < 10) {
> + if (argc < DM_VERITY_MANDATORY_ARGS) {
> ti->error = "Not enough arguments";
> r = -EINVAL;
> goto bad;
> @@ -1070,6 +1086,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> r = -EINVAL;
> goto bad;
> }
> + root_hash_digest_to_validate = argv[8];
>
> if (strcmp(argv[9], "-")) {
> v->salt_size = strlen(argv[9]) / 2;
> @@ -1087,19 +1104,28 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> }
> }
>
> - argv += 10;
> - argc -= 10;
> + argv += DM_VERITY_MANDATORY_ARGS;
> + argc -= DM_VERITY_MANDATORY_ARGS;

This cleanup should be in a separate patch in the series

>
> /* Optional parameters */
> if (argc) {
> as.argc = argc;
> as.argv = argv;
>
> - r = verity_parse_opt_args(&as, v);
> + r = verity_parse_opt_args(&as, v, &verify_args);
> if (r < 0)
> goto bad;
> }
>
> + /* Root hash signature is a optional parameter*/
> + r = verity_verify_root_hash(root_hash_digest_to_validate,
> + strlen(root_hash_digest_to_validate),
> + verify_args.sig,
> + verify_args.sig_size);
> + if (r < 0) {
> + ti->error = "Root hash verification failed";
> + goto bad;
> + }
> v->hash_per_block_bits =
> __fls((1 << v->hash_dev_block_bits) / v->digest_size);
>
> @@ -1165,9 +1191,13 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> ti->per_io_data_size = roundup(ti->per_io_data_size,
> __alignof__(struct dm_verity_io));
>
> + verity_verify_sig_opts_cleanup(&verify_args);
> +
> return 0;
>
> bad:
> +
> + verity_verify_sig_opts_cleanup(&verify_args);
> verity_dtr(ti);
>
> return r;
> diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c
> new file mode 100644
> index 000000000000..491c84eb58ef
> --- /dev/null
> +++ b/drivers/md/dm-verity-verify-sig.c
> @@ -0,0 +1,129 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Microsoft Corporation.
> + *
> + * Author: Jaskaran Singh Khurana <jaskarankhurana@linux.microsoft.com>
> + *
> + * This file is released under the GPLv2.
> + */
> +#include <linux/device-mapper.h>
> +#include <linux/verification.h>
> +#include "dm-verity.h"
> +#include "dm-verity-verify-sig.h"
> +
> +#define DM_VERITY_VERIFY_ERR(s) DM_VERITY_ROOT_HASH_VERIFICATION " " s
> +
> +bool verity_verify_is_sig_opt_arg(const char *arg_name)
> +{
> + return (!strcasecmp(arg_name,
> + DM_VERITY_ROOT_HASH_VERIFICATION_OPT_SIG));
> +}
> +EXPORT_SYMBOL_GPL(verity_verify_is_sig_opt_arg);
> +
> +int verity_verify_sig_parse_opt_args(struct dm_arg_set *as,
> + struct dm_verity *v,
> + struct dm_verity_sig_opts *sig_opts,
> + unsigned int *argc,
> + const char *arg_name)
> +{
> + const char *sig_size;
> + const char *sig_buf;
> + char dummy;
> + struct dm_target *ti = v->ti;
> + int r = 0;
> +
> + if (*argc < DM_VERITY_ROOT_HASH_VERIFICATION_OPTS - 1) {
> + ti->error = DM_VERITY_VERIFY_ERR("sig values not specified");

Can you can sig values to Signature values for readability

> + return -EINVAL;
> + }
> +
> + sig_size = dm_shift_arg(as);
> + (*argc)--;
> +
> + if (strcasecmp(arg_name, DM_VERITY_ROOT_HASH_VERIFICATION_OPT_SIG) ||
> + sscanf(sig_size, "%u%c",
> + &sig_opts->sig_size, &dummy) != 1) {
> + ti->error = DM_VERITY_VERIFY_ERR("invalid signature size");

Not sure why this is the best way to verifify the signature size

> + return -EINVAL;
> + }
> +
> + sig_buf = dm_shift_arg(as);
> + (*argc)--;
> +
> + if (strlen(sig_buf) != sig_opts->sig_size * 2) {
> + ti->error = DM_VERITY_VERIFY_ERR("sig buffer, size: mismatch");
> + return -EINVAL;
> + }

Can you explain the sig_opts->sig_size * 2 magic with a comment?

> +
> + sig_opts->sig = kmalloc(sig_opts->sig_size, GFP_KERNEL);
> + if (!sig_opts->sig) {
> + r = -ENOMEM;
> + goto end;

Good to check for NULL, but GFP_KERNEL will OOM if allocations fail

> + }
> +
> + r = hex2bin(sig_opts->sig, sig_buf, sig_opts->sig_size);
> +
> + if (r < 0) {
> + ti->error = DM_VERITY_VERIFY_ERR("invalid roothash sig buf");
> + r = -EINVAL;
> + goto end;
> + }
> +
> +end:
> + if (r < 0)
> + verity_verify_sig_opts_cleanup(sig_opts);
> + return r;
> +}
> +EXPORT_SYMBOL_GPL(verity_verify_sig_parse_opt_args);
> +
> +#ifdef CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG
> +/*
> + * verify_verify_roothash - Verify the root hash of the verity hash device
> + * using builtin trusted keys.
> + *
> + * @root_hash: For verity, the roothash/data to be verified.
> + * @root_hash_len: Size of the roothash/data to be verified.
> + * @sig_data: The trusted signature that verifies the roothash/data.
> + * @sig_len: Size of the signature.
> + *
> + */
> +int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
> + const void *sig_data, size_t sig_len)
> +{
> + int r;

ret?

> +
> + if (!root_hash || root_hash_len == 0)
> + return -EINVAL;
> +
> + if (!sig_data || sig_len == 0) {
> + if (IS_ENABLED(CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG_FORCE))
> + return -EINVAL;
> + else
> + return 0;
> + }
> +
> + r = verify_pkcs7_signature(root_hash, root_hash_len, sig_data, sig_len,
> + NULL, VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
> + NULL);
> + if (r < 0)
> + goto end;
> +
> +end:

goto end makes no sense if r is right down here, have you missed some code here?

Otherwise you can just remove the 4 lines above.

> + return r;
> +}
> +#else
> +int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
> + const void *sig_data, size_t sig_len)
> +{
> + return 0;
> +}
> +#endif
> +EXPORT_SYMBOL_GPL(verity_verify_root_hash);
> +
> +void verity_verify_sig_opts_cleanup(struct dm_verity_sig_opts *sig_opts)
> +{
> + kfree(sig_opts->sig);
> + sig_opts->sig = NULL;
> + sig_opts->sig_size = 0;
> +}
> +EXPORT_SYMBOL_GPL(verity_verify_sig_opts_cleanup);
> diff --git a/drivers/md/dm-verity-verify-sig.h b/drivers/md/dm-verity-verify-sig.h
> new file mode 100644
> index 000000000000..411808624d7e
> --- /dev/null
> +++ b/drivers/md/dm-verity-verify-sig.h
> @@ -0,0 +1,32 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Microsoft Corporation.
> + *
> + * Author: Jaskaran Singh Khurana <jaskarankhurana@linux.microsoft.com>
> + *
> + * This file is released under the GPLv2.
> + */
> +#ifndef DM_VERITY_SIG_VERIFICATION_H
> +#define DM_VERITY_SIG_VERIFICATION_H
> +
> +#define DM_VERITY_ROOT_HASH_VERIFICATION "DM Verity Sig Verification"
> +#define DM_VERITY_ROOT_HASH_VERIFICATION_OPT_SIG "root_hash_sig"
> +#define DM_VERITY_ROOT_HASH_VERIFICATION_OPTS 3
> +
> +struct dm_verity_sig_opts {
> + unsigned int sig_size;
> + u8 *sig;
> +};
> +
> +int verity_verify_root_hash(const void *data, size_t data_len,
> + const void *sig_data, size_t sig_len);
> +
> +bool verity_verify_is_sig_opt_arg(const char *arg_name);
> +
> +int verity_verify_sig_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
> + struct dm_verity_sig_opts *sig_opts,
> + unsigned int *argc, const char *arg_name);
> +
> +void verity_verify_sig_opts_cleanup(struct dm_verity_sig_opts *sig_opts);
> +
> +#endif /* DM_VERITY_SIG_VERIFICATION_H */

Balbir Singh.
>

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