| Message ID | 20241119104922.2772571-1-roberto.sassu@huaweicloud.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | integrity: Introduce the Integrity Digest Cache | expand |
On Tue, Nov 19, 2024 at 11:49:07AM +0100, Roberto Sassu wrote: > From: Roberto Sassu <roberto.sassu@huawei.com> > v5: > - Add new patch to introduce ksys_finit_module() Why? Luis
> On Nov 19, 2024, at 3:49 AM, Roberto Sassu <roberto.sassu@huaweicloud.com> wrote: > > From: Roberto Sassu <roberto.sassu@huawei.com> > > The Integrity Digest Cache can also help IMA for appraisal. IMA can simply > lookup the calculated digest of an accessed file in the list of digests > extracted from package headers, after verifying the header signature. It is > sufficient to verify only one signature for all files in the package, as > opposed to verifying a signature for each file. Is there a way to maintain integrity over time? Today if a CVE is discovered in a signed program, the program hash can be added to the blacklist keyring. Later if IMA appraisal is used, the signature validation will fail just for that program. With the Integrity Digest Cache, is there a way to do this?
On Tue, 2024-11-26 at 00:13 +0000, Eric Snowberg wrote: > > > On Nov 19, 2024, at 3:49 AM, Roberto Sassu <roberto.sassu@huaweicloud.com> wrote: > > > > From: Roberto Sassu <roberto.sassu@huawei.com> > > > > The Integrity Digest Cache can also help IMA for appraisal. IMA can simply > > lookup the calculated digest of an accessed file in the list of digests > > extracted from package headers, after verifying the header signature. It is > > sufficient to verify only one signature for all files in the package, as > > opposed to verifying a signature for each file. > > Is there a way to maintain integrity over time? Today if a CVE is discovered > in a signed program, the program hash can be added to the blacklist keyring. > Later if IMA appraisal is used, the signature validation will fail just for that > program. With the Integrity Digest Cache, is there a way to do this? As far as I can see, the ima_check_blacklist() call is before ima_appraise_measurement(). If it fails, appraisal with the Integrity Digest Cache will not be done. In the future, we might use the Integrity Digest Cache for blacklists too. Since a digest cache is reset on a file/directory change, IMA would have to revalidate the program digest against a new digest cache. Thanks Roberto
On Tue, Nov 19, 2024 at 11:49:07AM +0100, Roberto Sassu wrote: Hi Roberto, I hope the week is going well for you. > From: Roberto Sassu <roberto.sassu@huawei.com> > > Integrity detection and protection has long been a desirable feature, to > reach a large user base and mitigate the risk of flaws in the software > and attacks. > > However, while solutions exist, they struggle to reach a large user base, > due to requiring higher than desired constraints on performance, > flexibility and configurability, that only security conscious people are > willing to accept. > > For example, IMA measurement requires the target platform to collect > integrity measurements, and to protect them with the TPM, which introduces > a noticeable overhead (up to 10x slower in a microbenchmark) on frequently > used system calls, like the open(). > > IMA Appraisal currently requires individual files to be signed and > verified, and Linux distributions to rebuild all packages to include file > signatures (this approach has been adopted from Fedora 39+). Like a TPM, > also signature verification introduces a significant overhead, especially > if it is used to check the integrity of many files. > > This is where the new Integrity Digest Cache comes into play, it offers > additional support for new and existing integrity solutions, to make > them faster and easier to deploy. > > The Integrity Digest Cache can help IMA to reduce the number of TPM > operations and to make them happen in a deterministic way. If IMA knows > that a file comes from a Linux distribution, it can measure files in a > different way: measure the list of digests coming from the distribution > (e.g. RPM package headers), and subsequently measure a file if it is not > found in that list. > > The performance improvement comes at the cost of IMA not reporting which > files from installed packages were accessed, and in which temporal > sequence. This approach might not be suitable for all use cases. > > The Integrity Digest Cache can also help IMA for appraisal. IMA can simply > lookup the calculated digest of an accessed file in the list of digests > extracted from package headers, after verifying the header signature. It is > sufficient to verify only one signature for all files in the package, as > opposed to verifying a signature for each file. Roberto, a big picture question for you, our apologies if we completely misunderstand your patch series. The performance benefit comes from the fact that the kernel doesn't have to read a file and calculate the cryptographic digest when the file is accessed. The 'trusted' digest value comes from a signed list of digests that a packaging entity provides and the kernel validates. So there is an integrity guarantee that the supplied digests were the same as when the package was built. Is there a guarantee implemented, that we missed, that the on-disk file actually has the digest value that was initially generated by the packaging entity when the file is accessed operationally? Secondly, and in a related issue, what happens in a container environment when a pathname is accessed that is actually a different file but with the same effective pathname as a file that is in the vendor validated digest list? Once again, apologies, if we completely misinterpret the issues involved. Have a good remainder of the week. As always, Dr. Greg The Quixote Project - Flailing at the Travails of Cybersecurity https://github.com/Quixote-Project
On Wed, 2024-11-27 at 11:30 -0600, Dr. Greg wrote: > On Tue, Nov 19, 2024 at 11:49:07AM +0100, Roberto Sassu wrote: > > Hi Roberto, I hope the week is going well for you. > > > From: Roberto Sassu <roberto.sassu@huawei.com> > > > > Integrity detection and protection has long been a desirable feature, to > > reach a large user base and mitigate the risk of flaws in the software > > and attacks. > > > > However, while solutions exist, they struggle to reach a large user base, > > due to requiring higher than desired constraints on performance, > > flexibility and configurability, that only security conscious people are > > willing to accept. > > > > For example, IMA measurement requires the target platform to collect > > integrity measurements, and to protect them with the TPM, which introduces > > a noticeable overhead (up to 10x slower in a microbenchmark) on frequently > > used system calls, like the open(). > > > > IMA Appraisal currently requires individual files to be signed and > > verified, and Linux distributions to rebuild all packages to include file > > signatures (this approach has been adopted from Fedora 39+). Like a TPM, > > also signature verification introduces a significant overhead, especially > > if it is used to check the integrity of many files. > > > > This is where the new Integrity Digest Cache comes into play, it offers > > additional support for new and existing integrity solutions, to make > > them faster and easier to deploy. > > > > The Integrity Digest Cache can help IMA to reduce the number of TPM > > operations and to make them happen in a deterministic way. If IMA knows > > that a file comes from a Linux distribution, it can measure files in a > > different way: measure the list of digests coming from the distribution > > (e.g. RPM package headers), and subsequently measure a file if it is not > > found in that list. > > > > The performance improvement comes at the cost of IMA not reporting which > > files from installed packages were accessed, and in which temporal > > sequence. This approach might not be suitable for all use cases. > > > > The Integrity Digest Cache can also help IMA for appraisal. IMA can simply > > lookup the calculated digest of an accessed file in the list of digests > > extracted from package headers, after verifying the header signature. It is > > sufficient to verify only one signature for all files in the package, as > > opposed to verifying a signature for each file. > > Roberto, a big picture question for you, our apologies if we > completely misunderstand your patch series. Hi Greg no need to apologise, happy to answer your questions. > The performance benefit comes from the fact that the kernel doesn't > have to read a file and calculate the cryptographic digest when the > file is accessed. The 'trusted' digest value comes from a signed list > of digests that a packaging entity provides and the kernel validates. > So there is an integrity guarantee that the supplied digests were the > same as when the package was built. The performance benefit (for appraisal with my benchmark: 65% with sequential file access and 43% with parallel file access) comes from verifying the ECDSA signature of 303 digest lists, as opposed to the ECDSA signature of 12312 files. The additional performance boost due to switching from file data digest to fsverity digests is on top of that. > Is there a guarantee implemented, that we missed, that the on-disk > file actually has the digest value that was initially generated by the > packaging entity when the file is accessed operationally? Yes, the guarantee is provided by IMA by measuring the actual file digest and searching it in a digest cache. The integration in IMA of the Integrity Digest Cache is done in a separate patch set: https://lore.kernel.org/linux-security-module/20241119110103.2780453-1-roberto.sassu@huaweicloud.com/ The integrity evaluation result is invalidated when the file is modified, or when the digest list used to verify the file is modified too. For fsverity, the guarantee similarly comes from searching the fsverity digest in a digest cache, but as opposed of IMA the integrity evaluation result does not need to be invalidated for a file write, since fsverity-protected files are accessible only in read-only mode. However, the result still needs to be invalidated if the digest list changes. > Secondly, and in a related issue, what happens in a container > environment when a pathname is accessed that is actually a different > file but with the same effective pathname as a file that is in the > vendor validated digest list? At the moment nothing, only the file data are evaluated. Currently, the Integrity Digest Cache does not store the pathnames associated to a digest. It can be done as an extension, if desired, and the pathnames can be compared. Roberto > Once again, apologies, if we completely misinterpret the issues > involved. > > Have a good remainder of the week. > > As always, > Dr. Greg > > The Quixote Project - Flailing at the Travails of Cybersecurity > https://github.com/Quixote-Project
From: Roberto Sassu <roberto.sassu@huawei.com> Integrity detection and protection has long been a desirable feature, to reach a large user base and mitigate the risk of flaws in the software and attacks. However, while solutions exist, they struggle to reach a large user base, due to requiring higher than desired constraints on performance, flexibility and configurability, that only security conscious people are willing to accept. For example, IMA measurement requires the target platform to collect integrity measurements, and to protect them with the TPM, which introduces a noticeable overhead (up to 10x slower in a microbenchmark) on frequently used system calls, like the open(). IMA Appraisal currently requires individual files to be signed and verified, and Linux distributions to rebuild all packages to include file signatures (this approach has been adopted from Fedora 39+). Like a TPM, also signature verification introduces a significant overhead, especially if it is used to check the integrity of many files. This is where the new Integrity Digest Cache comes into play, it offers additional support for new and existing integrity solutions, to make them faster and easier to deploy. The Integrity Digest Cache can help IMA to reduce the number of TPM operations and to make them happen in a deterministic way. If IMA knows that a file comes from a Linux distribution, it can measure files in a different way: measure the list of digests coming from the distribution (e.g. RPM package headers), and subsequently measure a file if it is not found in that list. The performance improvement comes at the cost of IMA not reporting which files from installed packages were accessed, and in which temporal sequence. This approach might not be suitable for all use cases. The Integrity Digest Cache can also help IMA for appraisal. IMA can simply lookup the calculated digest of an accessed file in the list of digests extracted from package headers, after verifying the header signature. It is sufficient to verify only one signature for all files in the package, as opposed to verifying a signature for each file. The same approach can be followed by other LSMs, such as Integrity Policy Enforcement (IPE), and BPF LSM. The Integrity Digest Cache is not tied to a specific package format. The kernel supports a TLV-based digest list format. More can be added through third-party kernel modules. The TLV parser has been verified for memory safety with the Frama-C static analyzer. The version with the Frama-C assertions is available here: https://github.com/robertosassu/rpm-formal/blob/main/validate_tlv.c Integrating the Integrity Digest Cache in IMA brings significant performance improvements: up to 67% and 79% for measurement respectively in sequential and parallel file reads; up to 65% and 43% for appraisal respectively in sequential and parallel file reads. The performance can be further enhanced by using fsverity digests instead of conventional file digests, which would make IMA verify only the portion of the file to be read. However, at the moment, fsverity digests are not included in RPM packages. In this case, once rpm is extended to include them, Linux distributions still have to rebuild their packages. The Integrity Digest Cache can support both digest types, so that the functionality is immediately available without waiting for Linux distributions to do the transition. This patch set only includes the patches necessary to extract digests from a TLV-based data format, and exposes an API for LSMs to query them. A separate patch set will be provided to integrate it in IMA. This patch set and the follow-up IMA integration can be tested by following the instructions at: https://github.com/linux-integrity/digest-cache-tools This patch set applies on top of: https://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git/log/?h=next-integrity with commit 08ae3e5f5fc8 ("integrity: Use static_assert() to check struct sizes"). Changelog v5: - Remove the RPM parser and selftests (suggested by Linus) - Return digest cache pointer from digest_cache_lookup() - Export new Parser API, and allow registration of third-party digest list parsers (suggested by Mimi) - Reduce sizes in TLV format and remove TLV header (suggested by Jani Nikula) - Introduce new DIGEST_LIST_NUM_ENTRIES TLV field - Pass file descriptor instead of dentry in digest_cache_get() to properly detect potential deadlocks - Introduce digest_cache_opened_fd() to tell lockdep when it is safe to nest a mutex if digest_cache_get() is called with that mutex held - Add new patch to introduce ksys_finit_module() - Make the TLV parser as configurable (Y/N/m) with Kconfig (suggested by Mimi) - Don't store the path structure in the digest cache and pass it between creation and initialization of the digest cache - Remove digest_cache_dir_update_dig_user() and keep the digest cache retrieved during digest_cache_get() - Fail with an error pointer in digest_cache_dir_lookup_digest() if the current and passed directory digest cache don't match, or the digest cache was reset - Handle num_digest = 0 in digest_cache_htable_init() - Accept -EOPNOTSUPP error in digest_cache_new() - Implement inode_free_security_rcu LSM hook instead of inode_free_security - Move reservation of file descriptor security blob inside the #ifdef in init_ima_lsm() - Add test file_reset_again to check the error pointer returned by digest_cache_lookup() - Remove TLV_FAILURE_HDR_LEN TLV error test - Add missing MODULE_DESCRIPTION in kselftest kernel module (suggested by Jeff Johnson) - Replace dentry_open() with kernel_file_open() in populate.c and dir.c - Skip affected tests when CONFIG_DYNAMIC_FTRACE_WITH_ARGS=n v4: - Rename digest_cache LSM to Integrity Digest Cache (suggested by Paul Moore) - Update documentation - Remove forward declaration of struct digest_cache in include/linux/digest_cache.h (suggested by Jarkko) - Add DIGEST_CACHE_FREE digest cache event for notification - Remove digest_cache_found_t typedef and use uintptr_t instead - Add header callback in TLV parser and unexport tlv_parse_hdr() and tlv_parse_data() - Plug the Integrity Digest Cache into the 'ima' LSM - Switch from constructor to zeroing the object cache - Remove notifier and detect digest cache changes by comparing pointers - Rename digest_cache_dir_create() to digest_cache_dir_add_entries() - Introduce digest_cache_dir_create() to create and initialize a directory digest cache - Introduce digest_cache_dir_update_dig_user() to update dig_user with a file digest cache on positive digest lookup - Use up to date directory digest cache, to take into account possible inode eviction for the old ones - Introduce digest_cache_dir_prefetch() to prefetch digest lists - Adjust component name in debug messages (suggested by Jarkko) - Add FILE_PREFETCH and FILE_READ digest cache flags, remove RESET_USER - Reintroduce spin lock for digest cache verification data (needed for the selftests) - Get inode and file descriptor security blob offsets from outside (IMA) - Avoid user-after-free in digest_cache_unref() by decrementing the ref. count after printing the debug message - Check for digest list lookup loops also for the parent directory - Put and clear dig_owner directly in digest_cache_reset_clear_owner() - Move digest cache initialization code from digest_cache_create() to digest_cache_init() - Hold the digest list path until the digest cache is initialized (to avoid premature inode eviction) - Avoid race condition on setting DIR_PREFETCH in the directory digest cache - Introduce digest_cache_dir_prefetch() and do it between digest cache creation and initialization (to avoid lock inversion) - Avoid unnecessary length check in digest_list_parse_rpm() - Declare arrays of strings in tlv parser as static - Emit reset for parent directory on directory entry modification - Rename digest_cache_reset_owner() to digest_cache_reset_clear_owner() and digest_cache_reset_user() to digest_cache_clear_user() - Execute digest_cache_file_release() either if FMODE_WRITE or FMODE_CREATED are set in the file descriptor f_mode - Determine in digest_cache_verif_set() which gfp flag to use depending on verifier ID - Update selftests v3: - Rewrite documentation, and remove the installation instructions since they are now included in the README of digest-cache-tools - Add digest cache event notifier - Drop digest_cache_was_reset(), and send instead to asynchronous notifications - Fix digest_cache LSM Kconfig style issues (suggested by Randy Dunlap) - Propagate digest cache reset to directory entries - Destroy per directory entry mutex - Introduce RESET_USER bit, to clear the dig_user pointer on set/removexattr - Replace 'file content' with 'file data' (suggested by Mimi) - Introduce per digest cache mutex and replace verif_data_lock spinlock - Track changes of security.digest_list xattr - Stop tracking file_open and use file_release instead also for file writes - Add error messages in digest_cache_create() - Load/unload testing kernel module automatically during execution of test - Add tests for digest cache event notifier - Add test for ftruncate() - Remove DIGEST_CACHE_RESET_PREFETCH_BUF command in test and clear the buffer on read instead v2: - Include the TLV parser in this patch set (from user asymmetric keys and signatures) - Move from IMA and make an independent LSM - Remove IMA-specific stuff from this patch set - Add per algorithm hash table - Expect all digest lists to be in the same directory and allow changing the default directory - Support digest lookup on directories, when there is no security.digest_list xattr - Add seq num to digest list file name, to impose ordering on directory iteration - Add a new data type DIGEST_LIST_ENTRY_DATA for the nested data in the tlv digest list format - Add the concept of verification data attached to digest caches - Add the reset mechanism to track changes on digest lists and directory containing the digest lists - Add kernel selftests v1: - Add documentation in Documentation/security/integrity-digest-cache.rst - Pass the mask of IMA actions to digest_cache_alloc() - Add a reference count to the digest cache - Remove the path parameter from digest_cache_get(), and rely on the reference count to avoid the digest cache disappearing while being used - Rename the dentry_to_check parameter of digest_cache_get() to dentry - Rename digest_cache_get() to digest_cache_new() and add digest_cache_get() to set the digest cache in the iint of the inode for which the digest cache was requested - Add dig_owner and dig_user to the iint, to distinguish from which inode the digest cache was created from, and which is using it; consequently it makes the digest cache usable to measure/appraise other digest caches (support not yet enabled) - Add dig_owner_mutex and dig_user_mutex to serialize accesses to dig_owner and dig_user until they are initialized - Enforce strong synchronization and make the contenders wait until dig_owner and dig_user are assigned to the iint the first time - Move checking IMA actions on the digest list earlier, and fail if no action were performed (digest cache not usable) - Remove digest_cache_put(), not needed anymore with the introduction of the reference count - Fail immediately in digest_cache_lookup() if the digest algorithm is not set in the digest cache - Use 64 bit mask for IMA actions on the digest list instead of 8 bit - Return NULL in the inline version of digest_cache_get() - Use list_add_tail() instead of list_add() in the iterator - Copy the digest list path to a separate buffer in digest_cache_iter_dir() - Use digest list parsers verified with Frama-C - Explicitly disable (for now) the possibility in the IMA policy to use the digest cache to measure/appraise other digest lists - Replace exit(<value>) with return <value> in manage_digest_lists.c Roberto Sassu (15): lib: Add TLV parser module: Introduce ksys_finit_module() integrity: Introduce the Integrity Digest Cache digest_cache: Initialize digest caches digest_cache: Add securityfs interface digest_cache: Add hash tables and operations digest_cache: Allow registration of digest list parsers digest_cache: Parse tlv digest lists digest_cache: Populate the digest cache from a digest list digest_cache: Add management of verification data digest_cache: Add support for directories digest cache: Prefetch digest lists if requested digest_cache: Reset digest cache on file/directory change selftests/digest_cache: Add selftests for the Integrity Digest Cache docs: Add documentation of the Integrity Digest Cache Documentation/security/digest_cache.rst | 850 ++++++++++++++++++ Documentation/security/index.rst | 1 + MAINTAINERS | 10 + include/linux/digest_cache.h | 131 +++ include/linux/kernel_read_file.h | 1 + include/linux/syscalls.h | 10 + include/linux/tlv_parser.h | 32 + include/uapi/linux/tlv_digest_list.h | 47 + include/uapi/linux/tlv_parser.h | 41 + include/uapi/linux/xattr.h | 6 + kernel/module/main.c | 43 +- lib/Kconfig | 3 + lib/Makefile | 2 + lib/tlv_parser.c | 87 ++ lib/tlv_parser.h | 18 + security/integrity/Kconfig | 1 + security/integrity/Makefile | 1 + security/integrity/digest_cache/Kconfig | 43 + security/integrity/digest_cache/Makefile | 11 + security/integrity/digest_cache/dir.c | 400 +++++++++ security/integrity/digest_cache/htable.c | 260 ++++++ security/integrity/digest_cache/internal.h | 283 ++++++ security/integrity/digest_cache/main.c | 597 ++++++++++++ security/integrity/digest_cache/modsig.c | 66 ++ security/integrity/digest_cache/parsers.c | 257 ++++++ security/integrity/digest_cache/parsers/tlv.c | 341 +++++++ security/integrity/digest_cache/populate.c | 104 +++ security/integrity/digest_cache/reset.c | 227 +++++ security/integrity/digest_cache/secfs.c | 104 +++ security/integrity/digest_cache/verif.c | 135 +++ security/integrity/ima/ima.h | 1 + security/integrity/ima/ima_fs.c | 6 + security/integrity/ima/ima_main.c | 10 +- tools/testing/selftests/Makefile | 1 + .../testing/selftests/digest_cache/.gitignore | 3 + tools/testing/selftests/digest_cache/Makefile | 24 + .../testing/selftests/digest_cache/all_test.c | 769 ++++++++++++++++ tools/testing/selftests/digest_cache/common.c | 78 ++ tools/testing/selftests/digest_cache/common.h | 93 ++ .../selftests/digest_cache/common_user.c | 33 + .../selftests/digest_cache/common_user.h | 15 + tools/testing/selftests/digest_cache/config | 2 + .../selftests/digest_cache/generators.c | 130 +++ .../selftests/digest_cache/generators.h | 16 + .../selftests/digest_cache/testmod/Makefile | 16 + .../selftests/digest_cache/testmod/kern.c | 551 ++++++++++++ 46 files changed, 5849 insertions(+), 11 deletions(-) create mode 100644 Documentation/security/digest_cache.rst create mode 100644 include/linux/digest_cache.h create mode 100644 include/linux/tlv_parser.h create mode 100644 include/uapi/linux/tlv_digest_list.h create mode 100644 include/uapi/linux/tlv_parser.h create mode 100644 lib/tlv_parser.c create mode 100644 lib/tlv_parser.h create mode 100644 security/integrity/digest_cache/Kconfig create mode 100644 security/integrity/digest_cache/Makefile create mode 100644 security/integrity/digest_cache/dir.c create mode 100644 security/integrity/digest_cache/htable.c create mode 100644 security/integrity/digest_cache/internal.h create mode 100644 security/integrity/digest_cache/main.c create mode 100644 security/integrity/digest_cache/modsig.c create mode 100644 security/integrity/digest_cache/parsers.c create mode 100644 security/integrity/digest_cache/parsers/tlv.c create mode 100644 security/integrity/digest_cache/populate.c create mode 100644 security/integrity/digest_cache/reset.c create mode 100644 security/integrity/digest_cache/secfs.c create mode 100644 security/integrity/digest_cache/verif.c create mode 100644 tools/testing/selftests/digest_cache/.gitignore create mode 100644 tools/testing/selftests/digest_cache/Makefile create mode 100644 tools/testing/selftests/digest_cache/all_test.c create mode 100644 tools/testing/selftests/digest_cache/common.c create mode 100644 tools/testing/selftests/digest_cache/common.h create mode 100644 tools/testing/selftests/digest_cache/common_user.c create mode 100644 tools/testing/selftests/digest_cache/common_user.h create mode 100644 tools/testing/selftests/digest_cache/config create mode 100644 tools/testing/selftests/digest_cache/generators.c create mode 100644 tools/testing/selftests/digest_cache/generators.h create mode 100644 tools/testing/selftests/digest_cache/testmod/Makefile create mode 100644 tools/testing/selftests/digest_cache/testmod/kern.c