Re: [PATCH 1/1] efi_loader: CloseProtocol in efi_fmp_find

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Tue, Oct 11, 2022 at 01:12:18PM +0200, Heinrich Schuchardt wrote:
> 
> 
> On 10/11/22 13:08, Heinrich Schuchardt wrote:
> > 
> > 
> > On 10/11/22 09:35, AKASHI Takahiro wrote:
> > > On Tue, Oct 11, 2022 at 07:58:11AM +0200, Heinrich Schuchardt wrote:
> > > > 
> > > > 
> > > > On 10/11/22 02:49, AKASHI Takahiro wrote:
> > > > > The commit message is not accurate.
> > > > > 
> > > > > On Fri, Oct 07, 2022 at 04:06:23PM +0200, Heinrich Schuchardt wrote:
> > > > > > The CloseProtocol() boot service requires a handle as first argument.
> > > > > > Passing the protocol interface is incorrect.
> > > > > 
> > > > > Correct, but
> > > > > 
> > > > > > CloseProtocol() only has an effect if called with a non-zero value for
> > > > > > agent_handle. HandleProtocol() uses an opaque
> > > > > > agent_handle when invoking
> > > > > > OpenProtocol() (currently NULL).
> > > > > 
> > > > > No. OpenProtocol() is called with efi_root as an agent handle.
> > > > > So, calling CloseProtocol() is a right thing at the end.
> > > > 
> > > > Typically an agent handle is used to relate to a driver exposing
> > > > the driver
> > > > binding protocol.
> > > 
> > > Why can't we, other than a driver, call HandleProtocol()
> > > as a convenient way of accessing an interface?
> > 
> > The description of HandleProtocol() clearly says that it is deprecated.
> > 
> > The assumption that the UEFI specification makes in it is example code
> > that you never be able to close a protocol opened with HandleProtocol.
> > 
> > After the first usage of handle protocol the open protocol information
> > with the opaque agent handle will block the protocol interface from ever
> > being removed by the driver exposing it.
> > 
> > > 
> > > > The root node does not expose the driver binding protocol.
> > > 
> > > So do you mean the current implementation of HandleProtocol() is wrong?
> > 
> > Yes. If you ever install a boot time driver, it might remove a protocol
> > interface which is actually still in use.
> 
> Since 755d42d4209e ("efi_loader: correct HandleProtocol()") we set agent
> handle = efi_root in the implementation of HandleProtocol(). So this part is
> ok.

That is why I said using HandleProtocl() is valid and that
your commit message is not accurate.

-Takahiro Akashi


> Best regards
> 
> Heirnich
> 
> > 
> > > 
> > > > Why would you want to create an open protocol information entry here?
> > > 
> > > To access get_image_info() quickly.
> > 
> > This is not related to an open protocol information (see the UEFI spec
> > description of OpenProtocolInformation()).
> > 
> > Best regards
> > 
> > Heinrich
> > 
> > > 
> > > > Do you think anything with the code after the patch is wrong?
> > > 
> > > No reason to replace handle_protocol().
> > > 
> > > Another example is here:
> > > efi_load_image_from_path()
> > >      efi_handle_protocol(device, guid, (void **)&load_file_protocol));
> > >      ...
> > >      efi_close_protocol(device, guid, efi_root, NULL);
> > > 
> > > I believe that this function is anything but a driver.
> > > I think using HandleProtocol() (or preferably OpenProtocol()) and
> > > CloseProtocol()
> > > in pair seems totally sane.
> > > 
> > > -Takahiro Akashi
> > > 
> > > 
> > > 
> > > > Best regards
> > > > 
> > > > Heinrich
> > > > 
> > > > > 
> > > > > > Therefore HandleProtocol() should be
> > > > > > avoided.
> > > > > > 
> > > > > > * Replace the LocateHandle() call by efi_search_protocol().
> > > > > 
> > > > > LocateHandle() -> efi_handle_protocol()
> > > > > 
> > > > > So you could have fixed this way:
> > > > >       EFI_CALL(efi_close_protocol(handle, ..., &efi_root, NULL);
> > > > > 
> > > > > I preferred to use EFI_CALL() over this file as you can see.
> > > > > 
> > > > > -Takahiro Akashi
> > > > > 
> > > > > > * Remove the CloseProtocol() call.
> > > > > > 
> > > > > > Fixes: 8d99026f0697 ("efi_loader: capsule: support firmware update")
> > > > > > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> > > > > > ---
> > > > > >    lib/efi_loader/efi_capsule.c | 14 ++++++--------
> > > > > >    1 file changed, 6 insertions(+), 8 deletions(-)
> > > > > > 
> > > > > > diff --git a/lib/efi_loader/efi_capsule.c
> > > > > > b/lib/efi_loader/efi_capsule.c
> > > > > > index b6bd2d6af8..397e393a18 100644
> > > > > > --- a/lib/efi_loader/efi_capsule.c
> > > > > > +++ b/lib/efi_loader/efi_capsule.c
> > > > > > @@ -159,12 +159,14 @@ efi_fmp_find(efi_guid_t
> > > > > > *image_type, u8 image_index, u64 instance,
> > > > > >        efi_status_t ret;
> > > > > >        for (i = 0, handle = handles; i < no_handles; i++, handle++) {
> > > > > > -        ret = EFI_CALL(efi_handle_protocol(
> > > > > > -                *handle,
> > > > > > -                &efi_guid_firmware_management_protocol,
> > > > > > -                (void **)&fmp));
> > > > > > +        struct efi_handler *fmp_handler;
> > > > > > +
> > > > > > +        ret = efi_search_protocol(
> > > > > > +                *handle, &efi_guid_firmware_management_protocol,
> > > > > > +                &fmp_handler);
> > > > > >            if (ret != EFI_SUCCESS)
> > > > > >                continue;
> > > > > > +        fmp = fmp_handler->protocol_interface;
> > > > > >            /* get device's image info */
> > > > > >            info_size = 0;
> > > > > > @@ -215,10 +217,6 @@ efi_fmp_find(efi_guid_t
> > > > > > *image_type, u8 image_index, u64 instance,
> > > > > >    skip:
> > > > > >            efi_free_pool(package_version_name);
> > > > > >            free(image_info);
> > > > > > -        EFI_CALL(efi_close_protocol(
> > > > > > -                (efi_handle_t)fmp,
> > > > > > -                &efi_guid_firmware_management_protocol,
> > > > > > -                NULL, NULL));
> > > > > >            if (found)
> > > > > >                return fmp;
> > > > > >        }
> > > > > > -- 
> > > > > > 2.37.2
> > > > > >