Re: [PATCH v2 5/7] efi/capsule: Prepare for loading images with security header

[Jan Kiszka]

On 2017-03-28 19:23, Ard Biesheuvel wrote:
> On 28 March 2017 at 18:17, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>> On 28 March 2017 at 17:18, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote:
>>> On 2017-03-28 17:52, Ard Biesheuvel wrote:
>>>> On 28 March 2017 at 16:43, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote:
>>>>> On 2017-03-28 17:13, Jan Kiszka wrote:
>>>>>> On 2017-03-28 15:49, Ard Biesheuvel wrote:
>>>> [..]
>>>>>>> Could you please have a look at
>>>>>>>
>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=quark-capsule
>>>>>>>
>>>>>>> and tell me if that would work for you? I will send them out for
>>>>>>> proper review in any case, but to avoid confusion (if I missed
>>>>>>> something obvious), I don't want to send them out just yet.
>>>>>>
>>>>>> There is more needed to make things work again, maybe around passing the
>>>>>> right image size. I'm looking into this.
>>>>>>
>>>>>
>>>>> This makes CSH images being accepted again:
>>>>>
>>>>> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
>>>>> index 4b6f93f..a4e2311 100644
>>>>> --- a/arch/x86/platform/efi/quirks.c
>>>>> +++ b/arch/x86/platform/efi/quirks.c
>>>>> @@ -562,6 +562,8 @@ int efi_capsule_setup_info(struct capsule_info *cap_info, void *kbuff,
>>>>>  {
>>>>>         struct quark_security_header *csh = kbuff;
>>>>>
>>>>> +       cap_info->total_size = 0;
>>>>> +
>>>>>         if (!x86_match_cpu(quark_ids))
>>>>>                 goto fallback;
>>>>>
>>>>> @@ -587,12 +589,16 @@ int efi_capsule_setup_info(struct capsule_info *cap_info, void *kbuff,
>>>>>
>>>>>         kbuff += csh->headersize;
>>>>>
>>>>> +       cap_info->total_size = csh->headersize;
>>>>> +
>>>>>  fallback:
>>>>>         if (hdr_bytes < sizeof(efi_capsule_header_t))
>>>>>                 return 0;
>>>>>
>>>>>         memcpy(&cap_info->header, kbuff, sizeof(cap_info->header));
>>>>>
>>>>> +       cap_info->total_size += cap_info->header.imagesize;
>>>>> +
>>>>>         return __efi_capsule_setup_info(cap_info);
>>>>>  }
>>>>>
>>>>> diff --git a/drivers/firmware/efi/capsule-loader.c b/drivers/firmware/efi/capsule-loader.c
>>>>> index e851951..40dc354 100644
>>>>> --- a/drivers/firmware/efi/capsule-loader.c
>>>>> +++ b/drivers/firmware/efi/capsule-loader.c
>>>>> @@ -42,7 +42,7 @@ int __efi_capsule_setup_info(struct capsule_info *cap_info)
>>>>>         int ret;
>>>>>         void *temp_page;
>>>>>
>>>>> -       pages_needed = ALIGN(cap_info->header.imagesize, PAGE_SIZE) / PAGE_SIZE;
>>>>> +       pages_needed = ALIGN(cap_info->total_size, PAGE_SIZE) / PAGE_SIZE;
>>>>>
>>>>>         if (pages_needed == 0) {
>>>>>                 pr_err("invalid capsule size");
>>>>> @@ -59,7 +59,6 @@ int __efi_capsule_setup_info(struct capsule_info *cap_info)
>>>>>                 return ret;
>>>>>         }
>>>>>
>>>>> -       cap_info->total_size = cap_info->header.imagesize;
>>>>>         temp_page = krealloc(cap_info->pages,
>>>>>                              pages_needed * sizeof(void *),
>>>>>                              GFP_KERNEL | __GFP_ZERO);
>>>>> @@ -87,6 +86,8 @@ int __weak efi_capsule_setup_info(struct capsule_info *cap_info, void *kbuff,
>>>>>
>>>>>         memcpy(&cap_info->header, kbuff, sizeof(cap_info->header));
>>>>>
>>>>> +       cap_info->total_size = cap_info->header.imagesize;
>>>>> +
>>>>>         return __efi_capsule_setup_info(cap_info);
>>>>>  }
>>>>>
>>>>
>>>> OK, thanks for debugging that.
>>>>
>>>>> But then my changes to efi_capsule_update are missing the present the
>>>>> right format to the loader. As efi_capsule_update needs to lay out the
>>>>> sg-list in as special way, excluding the CSH on the first page, it needs
>>>>> to know about the displacement.
>>>>>
>>>>> Any suggestions how to address that without rolling back to my aproach?
>>>>>
>>>>
>>>> OK, I'm a bit lost now: for my understanding, could you please
>>>> reiterate how the CSH image deviates from the ordinary one? Or more
>>>> specifically, what exactly is preventing us from simply chopping off
>>>> the CSH header and pushing the capsule header + payload into
>>>> /dev/capsule_loader?
>>>>
>>>
>>> Devices that mandate a signed capsule for updates expect the CSH in
>>> front of the regular capsule image. The interface to UEFI remains
>>> unchanged, i.e. you pass the virtually chopped off capsule, but you have
>>> to leave the CSH in RAM right in front of that very same image. It's a
>>> "nice" side-channel API.
>>>
>>
>> Wow, that is worse than I thought.
>>
>> So my suggestion (which I coded up, please pull again),
> 
> Hmm, it does not build on x86 atm. Let me fix that up first (~15 min)
> 

I'm without access to the test device till next Tuesday. Will come back
to you then.

Jan

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