Re: [PATCH v4 4/7] ima: kexec: move ima log copy from kexec load to execute

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

On 1/24/24 08:11, Mimi Zohar wrote:
> On Mon, 2024-01-22 at 10:38 -0800, Tushar Sugandhi wrote:
>> ima_dump_measurement_list() is called during kexec 'load', which may
>> result in loss of IMA measurements during kexec soft reboot.  It needs
>> to be called during kexec 'execute'.
>>
>> The below changes need to be part of the same patch to ensure this
>> patch series remains bisect-safe by ensuring the IMA log gets copied over
>> during kexec soft reboot both before and after this patch.
>>
>> Implement ima_update_kexec_buffer() to be called during kexec 'execute'.
>> Move ima_dump_measurement_list() from ima_add_kexec_buffer() to
>> ima_update_kexec_buffer().  Make the necessary variables local static to
>> the file, so that they are accessible during both kexec 'load' - where
>> the memory is allocated and mapped to a segment in the new Kernel, and
>> during 'execute' - where the IMA log gets copied over.
>>
>> Implement kimage_file_post_load() and ima_kexec_post_load() to be invoked
>> after the new Kernel image has been loaded for kexec.
>> ima_kexec_post_load() will map the IMA buffer to a segment in the newly
>> loaded Kernel.  It will also register the reboot notifier_block to trigger
>> ima_update_kexec_buffer() at exec 'execute'.
> 
> This defines two new IMA hooks - ima_kexec_post_load() and
> ima_update_kexec_buffer().  They shouldn't be hidden here in the move of copying
> the measurement list from kexec load to execute.
> 
> If "ima_update_kexec_buffer()" was initially defined as a stub function, the
> infrastructure could be set up ahead of time.  This patch could then be limited
> to just moving the copy from kexec "load" to "execute", by replacing the stub
> function with the real function.
> 
Agreed.  Making ima_kexec_post_load() and ima_update_kexec_buffer() as 
stubs/hooks did cross my mind.  Thanks for confirming that.

I will split this patch (4/7) into two.

First will define the stubs, setup the infrastructure.
And second will move the copy from 'load' to 'execute'.

~Tushar
>> Modify kexec_file_load() syscall to call kimage_file_post_load() after the
>> image has been loaded and prepared for kexec.  Call it only on kexec soft
>> reboot and not for KEXEC_FILE_ON_CRASH.
>