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

AKASHI Takahiro
2019-02-27T06:55:01Z

On Wed, Feb 27, 2019 at 07:39:50AM +0100, Heinrich Schuchardt wrote:
> On 2/27/19 7:27 AM, AKASHI Takahiro wrote:
> > On Wed, Feb 27, 2019 at 07:14:10AM +0100, Heinrich Schuchardt wrote:
> >> 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.
> >
> > So is your answer yes, or no?
>
> I would prefer calling efi_get_variable() directly and not to use
> rs->get_variable().

My point is "including get_var()" or not.
I have never touched that function in my patch.

> >
> >> 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
> >
> > I'm not sure about your concern here, but no doubt efidebug should
> > be disabled on production system with secure boot.
>
> Also in efidebug we are creating more runtime code bytes than needed by
> using system->runtime->efi_something() or system->boottime->efi_something().

I think we discussed in the past.
I prefer to calling boot time/run time services via system table
as this command is expected to be implemented as an (embedded) EFI application
sometime in the future.

Thanks,
-Takahiro Akashi

> Best regards
>
> Heinrich
>
> >
> > Thanks,
> > -Takahiro Akashi
> >
> >> 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;
> >>>>>
> >>>>
> >>>
> >>
> >
>