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

[Heinrich Schuchardt]

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 at 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;
>>>
>>
>