From patchwork Sat Aug 3 06:08:26 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fan Wu X-Patchwork-Id: 13752189 X-Patchwork-Delegate: paul@paul-moore.com Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 88B6A14C5AF; Sat, 3 Aug 2024 06:08:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722665333; cv=none; b=G1O3u1IXKqQ1jpBnhl1FtNO8PDL/OsXnLGs9pwa0wh9BHWY4NkH5RcLOgvjOsJScdmfD0Z73orMjqzUX48LC1UBzAUH5qgnCedYeftid1o3nnVZX9mXDi42QOBcR781VESDPIZ7z4+0otoil4ffti9DE4t30ttRtklBxbT1RWEw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722665333; c=relaxed/simple; bh=SpeLY3QYrPLbzOwA/B5BeJ6wXSFfjK03mPw9BBljPGY=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References; b=V8kXOyVXXSgNX972HQFjrd33x3aoawO3+0LXKMJXUVvxq0ouJXRjVRmqwj+U7zrHmU1KPe4vqYlm7KSOfX1mOxIZWhf+KN14dFEHFsAolnXRZJVza9kxlAoUEMHKfrBQNfPsW5ND/4d45vGItLS+to2p41HbDIulw5g8hvoF/14= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=H6+LA1ib; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="H6+LA1ib" Received: by linux.microsoft.com (Postfix, from userid 1052) id BFCC620B7404; Fri, 2 Aug 2024 23:08:40 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com BFCC620B7404 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1722665320; bh=8NsYu1UcYZC/kqgFfh+6cO5zyAqSfnlh5D0qwSaBrTc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=H6+LA1ibEcYHuI7CB+EFnwO7WyrnzaFex41pjRy+d1zLez+EJMIjXHqdrwKEhe8lI HIUNJblsQ6ATFqs1qaivqaK3GiO2BzEme7CEecs2lhdMUmQ/Uh6NR/2DWc7CwOgiDJ OdYdeJVH/VlLuB8FNXmv4XOmw0i6/e1bqZOdWxIQ= From: Fan Wu To: corbet@lwn.net, zohar@linux.ibm.com, jmorris@namei.org, serge@hallyn.com, tytso@mit.edu, ebiggers@kernel.org, axboe@kernel.dk, agk@redhat.com, snitzer@kernel.org, mpatocka@redhat.com, eparis@redhat.com, paul@paul-moore.com Cc: linux-doc@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, fsverity@lists.linux.dev, linux-block@vger.kernel.org, dm-devel@lists.linux.dev, audit@vger.kernel.org, linux-kernel@vger.kernel.org, Deven Bowers , Fan Wu Subject: [PATCH v20 12/20] dm verity: expose root hash digest and signature data to LSMs Date: Fri, 2 Aug 2024 23:08:26 -0700 Message-Id: <1722665314-21156-13-git-send-email-wufan@linux.microsoft.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1722665314-21156-1-git-send-email-wufan@linux.microsoft.com> References: <1722665314-21156-1-git-send-email-wufan@linux.microsoft.com> Precedence: bulk X-Mailing-List: audit@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: From: Deven Bowers dm-verity provides a strong guarantee of a block device's integrity. As a generic way to check the integrity of a block device, it provides those integrity guarantees to its higher layers, including the filesystem level. However, critical security metadata like the dm-verity roothash and its signing information are not easily accessible to the LSMs. To address this limitation, this patch introduces a mechanism to store and manage these essential security details within a newly added LSM blob in the block_device structure. This addition allows LSMs to make access control decisions on the integrity data stored within the block_device, enabling more flexible security policies. For instance, LSMs can now revoke access to dm-verity devices based on their roothashes, ensuring that only authorized and verified content is accessible. Additionally, LSMs can enforce policies to only allow files from dm-verity devices that have a valid digital signature to execute, effectively blocking any unsigned files from execution, thus enhancing security against unauthorized modifications. The patch includes new hook calls, `security_bdev_setintegrity()`, in dm-verity to expose the dm-verity roothash and the roothash signature to LSMs via preresume() callback. By using the preresume() callback, it ensures that the security metadata is consistently in sync with the metadata of the dm-verity target in the current active mapping table. The hook calls are depended on CONFIG_SECURITY. Signed-off-by: Deven Bowers Signed-off-by: Fan Wu Reviewed-by: Mikulas Patocka --- v2: + No Changes v3: + No changes v4: + No changes v5: + No changes v6: + Fix an improper cleanup that can result in a leak v7: + Squash patch 08/12, 10/12 to [11/16] + Use part0 for block_device, to retrieve the block_device, when calling security_bdev_setsecurity v8: + Undo squash of 08/12, 10/12 - separating drivers/md/ from security/ & block/ + Use common-audit function for dmverity_signature. + Change implementation for storing the dm-verity digest to use the newly introduced dm_verity_digest structure introduced in patch 14/20. + Create new structure, dm_verity_digest, containing digest algorithm, size, and digest itself to pass to the LSM layer. V7 was missing the algorithm. + Create an associated public header containing this new structure and the key values for the LSM hook, specific to dm-verity. + Additional information added to commit, discussing the layering of the changes and how the information passed will be used. v9: + No changes v10: + No changes v11: + Add an optional field to save signature + Move the security hook call to the new finalize hook v12: + No changes v13: + No changes v14: + Correct code format + Remove unnecessary header and switch to dm_disk() v15: + Refactor security_bdev_setsecurity() to security_bdev_setintegrity() + Remove unnecessary headers v16: + Use kmemdup to duplicate signature + Clean up lsm blob data in error case v17: + Switch to depend on CONFIG_SECURITY + Use new enum name LSM_INT_DMVERITY_SIG_VALID v18: + Amend commit title + Fix incorrect error handling + Make signature exposure depends on CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG + Fix inaccurate comment + Remove include/linux/dm-verity.h + use crypto_ahash_alg_name(v->tfm) instead of v->alg_name v19: + Drop finalize callback and switch to preresume callback + Adding NULL check to avoid kmemdup when sig is NULL v20: + Adding more documentation regarding the new setintegrity hook call + Update the code for getting hash algorithm from either v->ahash_tfm or v->shash_tfm --- drivers/md/dm-verity-target.c | 118 ++++++++++++++++++++++++++++++++++ drivers/md/dm-verity.h | 6 ++ include/linux/security.h | 9 ++- 3 files changed, 132 insertions(+), 1 deletion(-) diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c index cf659c8feb29..24ba9a10444c 100644 --- a/drivers/md/dm-verity-target.c +++ b/drivers/md/dm-verity-target.c @@ -22,6 +22,7 @@ #include #include #include +#include #define DM_MSG_PREFIX "verity" @@ -930,6 +931,41 @@ static void verity_io_hints(struct dm_target *ti, struct queue_limits *limits) limits->dma_alignment = limits->logical_block_size - 1; } +#ifdef CONFIG_SECURITY + +static int verity_init_sig(struct dm_verity *v, const void *sig, + size_t sig_size) +{ + v->sig_size = sig_size; + + if (sig) { + v->root_digest_sig = kmemdup(sig, v->sig_size, GFP_KERNEL); + if (!v->root_digest_sig) + return -ENOMEM; + } + + return 0; +} + +static void verity_free_sig(struct dm_verity *v) +{ + kfree(v->root_digest_sig); +} + +#else + +static inline int verity_init_sig(struct dm_verity *v, const void *sig, + size_t sig_size) +{ + return 0; +} + +static inline void verity_free_sig(struct dm_verity *v) +{ +} + +#endif /* CONFIG_SECURITY */ + static void verity_dtr(struct dm_target *ti) { struct dm_verity *v = ti->private; @@ -949,6 +985,7 @@ static void verity_dtr(struct dm_target *ti) kfree(v->initial_hashstate); kfree(v->root_digest); kfree(v->zero_digest); + verity_free_sig(v); if (v->ahash_tfm) { static_branch_dec(&ahash_enabled); @@ -1418,6 +1455,13 @@ static int verity_ctr(struct dm_target *ti, unsigned int argc, char **argv) ti->error = "Root hash verification failed"; goto bad; } + + r = verity_init_sig(v, verify_args.sig, verify_args.sig_size); + if (r < 0) { + ti->error = "Cannot allocate root digest signature"; + goto bad; + } + v->hash_per_block_bits = __fls((1 << v->hash_dev_block_bits) / v->digest_size); @@ -1559,8 +1603,79 @@ int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest, unsigned i return 0; } +#ifdef CONFIG_SECURITY + +#ifdef CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG + +static int verity_security_set_signature(struct block_device *bdev, + struct dm_verity *v) +{ + /* + * if the dm-verity target is unsigned, v->root_digest_sig will + * be NULL, and the hook call is still required to let LSMs mark + * the device as unsigned. This information is crucial for LSMs to + * block operations such as execution on unsigned files + */ + return security_bdev_setintegrity(bdev, + LSM_INT_DMVERITY_SIG_VALID, + v->root_digest_sig, + v->sig_size); +} + +#else + +static inline int verity_security_set_signature(struct block_device *bdev, + struct dm_verity *v) +{ + return 0; +} + +#endif /* CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG */ + +/* + * Expose verity target's root hash and signature data to LSMs before resume. + * + * Returns 0 on success, or -ENOMEM if the system is out of memory. + */ +static int verity_preresume(struct dm_target *ti) +{ + struct block_device *bdev; + struct dm_verity_digest root_digest; + struct dm_verity *v; + int r; + + v = ti->private; + bdev = dm_disk(dm_table_get_md(ti->table))->part0; + root_digest.digest = v->root_digest; + root_digest.digest_len = v->digest_size; + if (static_branch_unlikely(&ahash_enabled) && !v->shash_tfm) + root_digest.alg = crypto_ahash_alg_name(v->ahash_tfm); + else + root_digest.alg = crypto_shash_alg_name(v->shash_tfm); + + r = security_bdev_setintegrity(bdev, LSM_INT_DMVERITY_ROOTHASH, &root_digest, + sizeof(root_digest)); + if (r) + return r; + + r = verity_security_set_signature(bdev, v); + if (r) + goto bad; + + return 0; + +bad: + + security_bdev_setintegrity(bdev, LSM_INT_DMVERITY_ROOTHASH, NULL, 0); + + return r; +} + +#endif /* CONFIG_SECURITY */ + static struct target_type verity_target = { .name = "verity", +/* Note: the LSMs depend on the singleton and immutable features */ .features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE, .version = {1, 10, 0}, .module = THIS_MODULE, @@ -1571,6 +1686,9 @@ static struct target_type verity_target = { .prepare_ioctl = verity_prepare_ioctl, .iterate_devices = verity_iterate_devices, .io_hints = verity_io_hints, +#ifdef CONFIG_SECURITY + .preresume = verity_preresume, +#endif /* CONFIG_SECURITY */ }; module_dm(verity); diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h index aac3a1b1d94a..ea2da450f173 100644 --- a/drivers/md/dm-verity.h +++ b/drivers/md/dm-verity.h @@ -45,6 +45,9 @@ struct dm_verity { u8 *salt; /* salt: its size is salt_size */ u8 *initial_hashstate; /* salted initial state, if shash_tfm is set */ u8 *zero_digest; /* digest for a zero block */ +#ifdef CONFIG_SECURITY + u8 *root_digest_sig; /* signature of the root digest */ +#endif /* CONFIG_SECURITY */ unsigned int salt_size; sector_t data_start; /* data offset in 512-byte sectors */ sector_t hash_start; /* hash start in blocks */ @@ -58,6 +61,9 @@ struct dm_verity { bool hash_failed:1; /* set if hash of any block failed */ bool use_bh_wq:1; /* try to verify in BH wq before normal work-queue */ unsigned int digest_size; /* digest size for the current hash algorithm */ +#ifdef CONFIG_SECURITY + unsigned int sig_size; /* root digest signature size */ +#endif /* CONFIG_SECURITY */ unsigned int hash_reqsize; /* the size of temporary space for crypto */ enum verity_mode mode; /* mode for handling verification errors */ unsigned int corrupted_errs;/* Number of errors for corrupted blocks */ diff --git a/include/linux/security.h b/include/linux/security.h index 39aec1c96d6a..0604893f2f9e 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -83,8 +83,15 @@ enum lsm_event { LSM_POLICY_CHANGE, }; +struct dm_verity_digest { + const char *alg; + const u8 *digest; + size_t digest_len; +}; + enum lsm_integrity_type { - __LSM_INT_MAX + LSM_INT_DMVERITY_SIG_VALID, + LSM_INT_DMVERITY_ROOTHASH, }; /*