Re: [PATCH 00/10] ima: measure events between kexec load and execute

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

Thanks Dave for taking a look at this.

I will keep Eric looped in on the next versions of this
patch series.

~Tushar

On 7/7/23 01:18, Dave Young wrote:
> [Add Eric in cc]
>
> On Tue, 4 Jul 2023 at 05:58, Tushar Sugandhi
> <tusharsu@linux.microsoft.com> wrote:
>> 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'.
>>
>> Some devices can be configured to call kexec 'load' first, and followed
>> by kexec 'execute' after some time. (as opposed to calling 'load' and
>> 'execute' in one single kexec command).  In such scenario, if new IMA
>> measurements are added between kexec 'load' and kexec 'execute', the
>> TPM PCRs are extended with the IMA events between 'load' and 'execute';
>> but those IMA events are not carried over to the new kernel after kexec
>> soft reboot.  This results in mismatch between TPM PCR quotes and the
>> actual IMA measurements list after the device boots into the new kexec
>> image.  This mismatch results in the remote attestation failing for that
>> device.
>>
>> This patch series proposes a solution to solve this problem by allocating
>> the necessary buffer at kexec 'load' time, and populating the buffer
>> with the IMA measurements at kexec 'execute' time.
>>
>> The solution includes:
>>   - addition of new functionality to allocate a buffer to hold IMA
>>     measurements at kexec 'load',
>>
>>   - ima functionality to suspend and resume measurements as needed during
>>     buffer copy at kexec 'execute',
>>
>>   - ima functionality for mapping the measurement list 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',
>>
>>   - and removal of deprecated functions.
>>
>> The modifications 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.
>>
>> 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@linux.vnet.ibm.com/
>>
>> [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@linux.vnet.ibm.com/T/
>>
>> Tushar Sugandhi (10):
>>    ima: implement function to allocate buffer at kexec load
>>    ima: implement function to populate buffer at kexec execute
>>    ima: allocate buffer at kexec load to hold ima measurements
>>    ima: implement functions to suspend and resume measurements
>>    kexec: implement functions to map and unmap segment to kimage
>>    ima: update buffer at kexec execute with ima measurements
>>    ima: remove function ima_dump_measurement_list
>>    ima: implement and register a reboot notifier function to update kexec
>>      buffer
>>    ima: suspend measurements while the kexec buffer is being copied
>>    kexec: update kexec_file_load syscall to call ima_kexec_post_load
>>
>>   include/linux/ima.h                |   3 +
>>   include/linux/kexec.h              |  13 ++
>>   kernel/kexec_core.c                |  72 +++++++++-
>>   kernel/kexec_file.c                |   7 +
>>   kernel/kexec_internal.h            |   1 +
>>   security/integrity/ima/ima.h       |   4 +
>>   security/integrity/ima/ima_kexec.c | 211 +++++++++++++++++++++++------
>>   security/integrity/ima/ima_queue.c |  32 +++++
>>   8 files changed, 295 insertions(+), 48 deletions(-)
>>
>> --
>> 2.25.1
>>
>>
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>> kexec@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec
>>

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