[U-Boot] [PATCH v2 1/5] efi_loader: bootmgr: support BootNext and BootCurrent variable behavior

Heinrich Schuchardt
2019-02-27T06:14:10Z

On 2/27/19 6:47 AM, AKASHI Takahiro wrote:
> On Tue, Feb 26, 2019 at 07:57:26PM +0100, Heinrich Schuchardt wrote:
>> On 1/15/19 3:54 AM, AKASHI Takahiro wrote:
>>> See UEFI v2.7, section 3.1.2 for details of the specification.
>>>
>>> With my efitool command, you can try as the following:
>>> => efi boot add 1 SHELL ...
>>> => efi boot add 2 HELLO ...
>>> => efi boot order 1 2
>>> => efi bootmgr
>>> (starting SHELL ...)
>>> => efi boot next 2
>>> => efi bootmgr
>>> (starting HELLO ...)
>>> => efi dumpvar
>>> <snip ...>
>>> BootCurrent: {boot,run}(blob)
>>> 00000000: 02 00 ..
>>> BootOrder: {boot,run}(blob)
>>> 00000000: 01 00 02 00 ....
>>>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>> ---
>>> lib/efi_loader/efi_bootmgr.c | 34 +++++++++++++++++++++++++++++++++-
>>> 1 file changed, 33 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/lib/efi_loader/efi_bootmgr.c b/lib/efi_loader/efi_bootmgr.c
>>> index a095df3f540b..6c5303736dc6 100644
>>> --- a/lib/efi_loader/efi_bootmgr.c
>>> +++ b/lib/efi_loader/efi_bootmgr.c
>>> @@ -145,11 +145,21 @@ static void *try_load_entry(uint16_t n, struct efi_device_path **device_path,
>>> efi_deserialize_load_option(&lo, load_option);
>>>
>>> if (lo.attributes & LOAD_OPTION_ACTIVE) {
>>> + u32 attributes;
>>> efi_status_t ret;
>>>
>>> debug("%s: trying to load \"%ls\" from %pD\n",
>>> __func__, lo.label, lo.file_path);
>>>
>>> + attributes = EFI_VARIABLE_BOOTSERVICE_ACCESS |
>>> + EFI_VARIABLE_RUNTIME_ACCESS;
>>> + size = sizeof(n);
>>> + ret = rs->set_variable(L"BootCurrent",
>>> + (efi_guid_t *)&efi_global_variable_guid,
>>
>> Use EFI_CALL().
>
> Okay
> But as I said somewhere else, it's quite annoying to me that
> some efi_xxx requires EFI_CALL(), and others not.
> There should have been consistent naming rules.

We started with having separate functions like efi_allocate_pages_ext()
and efi_allocate_pages(). Then Rob Clark came along and introduced
EFI_CALL() in a095aadffa96 and I stopped creating _ext() functions.

When running with DEBUG 1 it sometimes is helpful to see which function
is calling which other and where errors are originally reported.

But I am open to changes in this area.

>
>> Instead of dereferencing you could directly call
>> efi_set_variable().
>
> Yeah, given that this code is under lib/efi_loader, it may be natural
> to use efi_set_variable(). But existing get_var() uses the same style of coding.
>
> Do you want to change all of the call sites including get_var()?

Calling efi_set_variable() directly uses less bytes of code than
rs->get_variable() which makes it preferable.

I have seen that iPXE modifies system->boottime to intercept system
calls. The same could be done by an EFI driver to the runtime vectors.

In the light of your work on secure boot I think we should not allow an
EFI driver to intercept the reading and changing of variables here.

We should also rethink it for efidebug.c

Best regards

Heinrich

>
>>> + attributes, size, &n);
>>> + if (ret != EFI_SUCCESS)
>>> + goto error;
>>> +
>>> ret = efi_load_image_from_path(lo.file_path, &image);
>>>
>>> if (ret != EFI_SUCCESS)
>>> @@ -173,16 +183,38 @@ error:
>>> void *efi_bootmgr_load(struct efi_device_path **device_path,
>>> struct efi_device_path **file_path)
>>> {
>>> - uint16_t *bootorder;
>>> + u16 bootnext, *bootorder;
>>> efi_uintn_t size;
>>> void *image = NULL;
>>> int i, num;
>>> + efi_status_t ret;
>>>
>>> __efi_entry_check();
>>>
>>> bs = systab.boottime;
>>> rs = systab.runtime;
>>>
>>> + /* get BootNext */
>>> + size = sizeof(bootnext);
>>> + ret = rs->get_variable(L"BootNext",
>>> + (efi_guid_t *)&efi_global_variable_guid,
>>> + NULL, &size, &bootnext);
>>
>> You could call efi_get_variable() directly instead of dereferencing rs.
>> But anyway you have to use EFI_CALL().
>
> Ditto
>
>>> + if (!bootnext)
>>> + goto run_list;
>>
>> Goto is acceptable for error handling. But otherwise I would rather
>> avoid it.
>
> Okay with another indentation.
>
>>> +
>>> + /* delete BootNext */
>>> + ret = rs->set_variable(L"BootNext",
>>> + (efi_guid_t *)&efi_global_variable_guid,
>>> + 0, 0, &bootnext);
>>
>> EFI_CALL().
>
> Thanks,
> -Takahiro Akashi
>
>> Best regards
>>
>> Heinrich
>>
>>> + if (ret != EFI_SUCCESS)
>>> + goto error;
>>> +
>>> + image = try_load_entry(bootnext, device_path, file_path);
>>> + if (image)
>>> + goto error;
>>> +
>>> +run_list:
>>> + /* BootOrder */
>>> bootorder = get_var(L"BootOrder", &efi_global_variable_guid, &size);
>>> if (!bootorder)
>>> goto error;
>>>
>>
>