The current Kernel behavior is IMA measurements snapshot is taken at kexec 'load' and not at kexec 'execute'. IMA log is then carried over to the new Kernel after kexec 'execute'. New events can be measured during/after the IMA log snapshot at kexec 'load' and before the system boots to the new Kernel. In this scenario, the TPM PCRs are extended with these events, but they are not carried over to the new Kernel after kexec soft reboot since the snapshot is already taken. This results in mismatch between TPM PCR quotes and the actual IMA measurements list after kexec soft reboot, which in turn results in remote attestation failure. To solve this problem allocate the necessary buffer at kexec 'load' time, populate the buffer with the IMA measurements at kexec 'execute' time, and measure two new IMA events 'kexec_load' and 'kexec_execute' as critical data to help detect missing events after kexec soft reboot. The solution details include: - refactoring the existing code to allocate a buffer to hold IMA measurements at kexec 'load', and dump the measurements at kexec 'execute' - IMA functionality to suspend and resume measurements as needed during buffer copy at kexec 'execute', - kexec functionality for mapping the segments from the current Kernel to the subsequent one, - necessary changes to the kexec_file_load syscall, enabling it to call the ima functions, - registering a reboot notifier which gets called during kexec 'execute', - introducing a new Kconfig option to configure the extra memory to be allocated for passing IMA log from the current Kernel to the next, - introducing two new events to be measured by IMA during kexec, to help diagnose if the IMA log was copied fully or partially, from the current Kernel to the next, - excluding IMA segment while calculating and storing digest in function kexec_calculate_store_digests(), since IMA segment can be modified after the digest is computed during kexec 'load'. This will ensure that the segment is not added to the 'purgatory_sha_regions', and thus not verified by verify_sha256_digest(). The changes proposed in this series ensure the integrity of the IMA measurements is preserved across kexec soft reboots, thus significantly improving the security of the Kernel post kexec soft reboots. There were previous attempts to fix this issue [1], [2], [3]. But they were not merged into the mainline Kernel. We took inspiration from the past work [1] and [2] while working on this patch series. V3 of this series is available here[5] for reference. References: ----------- [1] [PATHC v2 5/9] ima: on soft reboot, save the measurement list https://lore.kernel.org/lkml/1472596811-9596-6-git-send-email-zohar@xxxxxxxxxxxxxxxxxx/ [2] PATCH v2 4/6] kexec_file: Add mechanism to update kexec segments. https://lkml.org/lkml/2016/8/16/577 [3] [PATCH 1/6] kexec_file: Add buffer hand-over support https://lore.kernel.org/linuxppc-dev/1466473476-10104-6-git-send-email-bauerman@xxxxxxxxxxxxxxxxxx/T/ [4] [PATCH v2 0/7] ima: kexec: measure events between kexec load and execute https://lore.kernel.org/all/20231005182602.634615-1-tusharsu@xxxxxxxxxxxxxxxxxxx/ [5] [PATCH v3 0/7] ima: kexec: measure events between kexec load and execute https://lore.kernel.org/all/20231216010729.2904751-1-tusharsu@xxxxxxxxxxxxxxxxxxx/ Change Log v4: - Incorporated feedback from the community (Stefan Berger and Mimi Zohar) on v3 of this series[5]. - Rearranged patches so that they remain bisect-safe i.e. the system can go through kexec soft reboot, and IMA log is carried over after each patch. - Verified all the patches are bisect-safe by booting into each patch and verifying kexec soft reboot works, and IMA log gets carried over. - Suspend-resume measurements is now a separate patch (patch #5) and all the relevant code is part of the same patch. - Excluding IMA segment from segment digest verification is now a separate patch. (patch #3). - Registering reboot notifier and functions related to move ima log copy from kexec load to execute are now part of the same patch (patch #4) to protect bisect-safeness of the series. - Updated the title of patch #6 as per the feedback. - The default value of kexec extra memory for IMA measurements is set to half the PAGESIZE to maintain backwards compatibility. - Added number of IMA measurement records as part of 'kexec_load' and 'kexec_execute' IMA critical data events. - Updated patch descriptions as necessary. Change Log v3: - Incorporated feedback from the community (Stefan Berger and Mimi Zohar) on v2 of this series[4]. - Renamed functions and removed extraneous checks and code comments. - Updated patch descriptions and titles as necessary. - Updated kexec_calculate_store_digests() in patch 2/7 to exclude ima segment from calculating and storing digest. - Updated patch 3/7 to use kmalloc_array instead of kmalloc and freed memory early to avoid potential memory leak. - Updated patch 6/7 to change Kconfig option IMA_KEXEC_EXTRA_PAGES to IMA_KEXEC_EXTRA_MEMORY_KB to allocate the memory in kb rather than in number of pages. - Optimized patch 7/7 not to free and alloc memory if the buffer size hasn't changed during multiple kexec 'load' operations. - Fixed a bug in patch 7/7 to measure multiple 'kexec_load' events even if buffer size hasn't changed. - Verified the patches are bisect-safe by compiling and booting into each patch individually. Change Log v2: - Incorporated feedback from the community on v1 series. - Refactored the existing ima_dump_measurement_list to move buffer allocation functionality to ima_alloc_kexec_buf() function. - Introduced a new Kconfig option to configure the memory. - Updated the logic to copy the IMA log only in case of kexec soft reboot, and not on kexec crash. - Updated the logic to copy as many IMA events as possible in case of memory constraint, rather than just bailing out. - Introduced two new events to be measured by IMA during kexec, to help diagnose if the IMA log was copied fully or partially from the current Kernel to the next. - Refactored patches to ensure no warnings during individual patch compilation. - Used virt_to_page instead of phys_to_page. - Updated patch descriptions as necessary. Tushar Sugandhi (7): ima: define and call ima_alloc_kexec_file_buf kexec: define functions to map and unmap segments ima: kexec: skip IMA segment validation after kexec soft reboot ima: kexec: move ima log copy from kexec load to execute ima: suspend measurements during buffer copy at kexec execute ima: make the kexec extra memory configurable ima: measure kexec load and exec events as critical data include/linux/ima.h | 3 + include/linux/kexec.h | 16 +++ kernel/kexec_core.c | 59 +++++++- kernel/kexec_file.c | 16 +++ security/integrity/ima/Kconfig | 11 ++ security/integrity/ima/ima.h | 2 + security/integrity/ima/ima_kexec.c | 220 ++++++++++++++++++++++++----- security/integrity/ima/ima_queue.c | 32 +++++ 8 files changed, 319 insertions(+), 40 deletions(-) -- 2.25.1
