Re: [PATCH 10/10] kexec: update kexec_file_load syscall to call ima_kexec_post_load

From: Tushar Sugandhi <tusharsu@linux.microsoft.com>
To: RuiRui Yang <ruyang@redhat.com>
Cc: zohar@linux.ibm.com, noodles@fb.com, bauermann@kolabnow.com,
	kexec@lists.infradead.org, linux-integrity@vger.kernel.org,
	code@tyhicks.com, nramas@linux.microsoft.com,
	paul@paul-moore.com, Eric Biederman <ebiederm@xmission.com>
Subject: Re: [PATCH 10/10] kexec: update kexec_file_load syscall to call ima_kexec_post_load
Date: Tue, 11 Jul 2023 12:14:55 -0700	[thread overview]
Message-ID: <b4047d8d-2c7c-e357-1c1f-cc55978fd963@linux.microsoft.com> (raw)
In-Reply-To: <CALu+AoQC101fcbJjLdJHD7QtqeXzt5uOZDgNYvob0U_NGyaqCQ@mail.gmail.com>

On 7/7/23 01:20, RuiRui Yang wrote:
> On Tue, 4 Jul 2023 at 05:58, Tushar Sugandhi
> <tusharsu@linux.microsoft.com> wrote:
>> The kexec_file_load syscall is used to load a new kernel for kexec.
>> The syscall needs to update its function to call ima_kexec_post_load, which
>> was implemented in a previous patch.  ima_kexec_post_load takes care of
>> mapping the measurement list for the next kernel and registering a reboot
>> notifier if it's not already registered.
>>
>> Modify the kexec_file_load syscall to call ima_kexec_post_load after the
>> image has been loaded and prepared for kexec.  This ensures that the IMA
>> measurement list will be available to the next kernel after a kexec reboot.
>> This also ensures the measurements taken in the window between kexec load
>> and execute are captured and passed to the next kernel.
>>
>> Declare the kimage_file_post_load function in the kernel/kexec_internal.h,
>> so it can be properly used in the syscall.
>>
>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>> ---
>>   kernel/kexec_file.c     | 7 +++++++
>>   kernel/kexec_internal.h | 1 +
>>   2 files changed, 8 insertions(+)
>>
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index f989f5f1933b..efe28e77280c 100644
>> --- a/kernel/kexec_file.c
>> +++ b/kernel/kexec_file.c
>> @@ -184,6 +184,11 @@ kimage_validate_signature(struct kimage *image)
>>   }
>>   #endif
>>
>> +void kimage_file_post_load(struct kimage *image)
>> +{
>> +       ima_kexec_post_load(image);
>> +}
>> +
>>   /*
>>    * In file mode list of segments is prepared by kernel. Copy relevant
>>    * data from user space, do error checking, prepare segment list
>> @@ -399,6 +404,8 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
>>
>>          kimage_terminate(image);
>>
>> +       kimage_file_post_load(image);
> I think it should be only done for the reboot case,  please just
> exclude the kdump case here..
>
Thanks for the feedback RuiRui.  Appreciate it.

Conceptually I agree with you that this needs to be done only for reboot.
I need to figure out how to do it implementation wise.

If you can give me pointers/suggestions, that would help.

~Tushar
>> +
>>          ret = machine_kexec_post_load(image);
>>          if (ret)
>>                  goto out;
>> diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h
>> index 74da1409cd14..98dd5fcafaf0 100644
>> --- a/kernel/kexec_internal.h
>> +++ b/kernel/kexec_internal.h
>> @@ -30,6 +30,7 @@ static inline void kexec_unlock(void)
>>
>>   #ifdef CONFIG_KEXEC_FILE
>>   #include <linux/purgatory.h>
>> +void kimage_file_post_load(struct kimage *image);
>>   void kimage_file_post_load_cleanup(struct kimage *image);
>>   extern char kexec_purgatory[];
>>   extern size_t kexec_purgatory_size;
>> --
>> 2.25.1
>>
>>
>> _______________________________________________
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>>