Re: [PATCH v2 2/3] efi_loader: bootmgr: fix a problem in loading an image from a short-path

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

On Thu, May 12, 2022 at 08:50:34AM +0200, Heinrich Schuchardt wrote:
> On 5/12/22 04:29, AKASHI Takahiro wrote:
> > Booting from a short-form device path which starts with the first element
> > being a File Path Media Device Path failed because it doesn't contain
> > any valid device with simple file system protocol and efi_dp_find_obj()
> > in efi_load_image_from_path() will return NULL.
> > For instance,
> > /VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b)/Scsi(0,0)/\helloworld.efi
> > -> shortened version: /\helloworld.efi
> > 
> > With this patch applied, all the media devices with simple file system
> > protocol are enumerated and the boot manager attempts to boot temporarily
> > generated device paths one-by-one.
> > 
> > This new implementation is still a bit incompatible with the UEFI
> > specification in terms of:
> > * not creating real boot options
> > * not try
> >    "If a device does not support the EFI_SIMPLE_FILE_SYSTEM_PROTOCOL, but
> >    supports the EFI_BLOCK_IO_PROTOCOL protocol, then the EFI Boot Service
> >    ConnectController must be called for this device with DriverImageHandle
> >    and RemainingDevicePath set to NULL and the Recursive flag is set to TRUE."
> 
> We already have the ConnectController() logic in lib/efi_driver/. We
> just have to carry it to all block devices (in a future patch set).
> 
> > (See section 3.1.2 "Load Option Processing".)
> > 
> > But it still gives us a closer and better solution than the current.
> > 
> > Fixes: commit 9cdf470274ff ("efi_loader: support booting via short-form device-path")
> > Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> > ---
> >   lib/efi_loader/efi_bootmgr.c | 98 ++++++++++++++++++++++++++++++++++--
> >   1 file changed, 94 insertions(+), 4 deletions(-)
> > 
> > diff --git a/lib/efi_loader/efi_bootmgr.c b/lib/efi_loader/efi_bootmgr.c
> > index 631a25d76e9e..3608e433503e 100644
> > --- a/lib/efi_loader/efi_bootmgr.c
> > +++ b/lib/efi_loader/efi_bootmgr.c
> > @@ -76,6 +76,91 @@ struct efi_device_path *expand_media_path(struct efi_device_path *device_path)
> >   	return full_path;
> >   }
> > 
> 
> The logic in this patch looks good to me. Just some nits:
> 
> Please, provide a description of the function and its parameters.

I don't think we need a description here because, as you can see,
__try_load() is an inner function and intended to be called only from
try_load_from_short_path(). The purpose of extracting it is to avoid
a duplicated code to go though a list of handles *twice*,
for removable media and for fixed media.

The description of try_load_from_short_path() covers both.

> > +static efi_status_t __try_load(efi_handle_t *fs_handles, efi_uintn_t num,
> 
> Please, use a name not starting with underscores conveying what the
> function is good for, e.g. efi_load_from_file_path().
> 
> > +			       struct efi_device_path *fp,
> > +			       efi_handle_t *handle, bool removable)
> > +{
> > +	struct efi_handler *handler;
> > +	struct efi_device_path *dp;
> > +	int i;
> > +	efi_status_t ret;
> > +
> > +	for (i = 0; i < num; i++) {
> > +		if (removable && !efi_disk_is_removable(fs_handles[i]))
> > +			continue;
> > +		if (!removable && efi_disk_is_removable(fs_handles[i]))
> > +			continue;
> > +
> > +		ret = efi_search_protocol(fs_handles[i], &efi_guid_device_path,
> > +					  &handler);
> > +		if (ret != EFI_SUCCESS)
> > +			/* unlikely */
> 
> If you want to tell the compiler that this path is unlikely:
> 
> 	        if (unlikely(ret != EFI_SUCCESS))
> 
> But as this code is not called often I would simply remove the comment.
> 
> > +			continue;
> > +
> > +		dp = handler->protocol_interface;
> > +		if (!dp)
> > +			/* unlikely */
> 
> ditto
> 
> > +			continue;
> > +
> > +		dp = efi_dp_append(dp, fp);
> 
> You are leaking the original dp here. Please, avoid memory leaks.

Actually, not.
The original dp comes from "handler->protocol_interface" and it should
exist while the associated handle, (fs_handles[i]), exists.

-Takahiro Akashi

> 
> > +		if (!dp)
> > +			/* unlikely */
> 
> if (unlikely( ?
> 
> > +			continue;
> > +
> > +		ret = EFI_CALL(efi_load_image(true, efi_root, dp, NULL, 0,
> > +					      handle));
> > +		efi_free_pool(dp);
> > +		if (ret == EFI_SUCCESS)
> > +			return ret;
> > +	}
> > +
> > +	return EFI_NOT_FOUND;
> > +}
> > +
> > +/**
> > + * try_load_from_short_path
> > + * @fp:		file path
> > + * @handle:	pointer to handle for newly installed image
> > + *
> > + * Enumerate all the devices which support file system operations,
> > + * prepend its media device path to the file path, @fp, and
> > + * try to load the file.
> > + * This function should be called when handling a short-form path
> > + * which is starting with a file device path.
> > + *
> > + * Return:	status code
> > + */
> > +static efi_status_t try_load_from_short_path(struct efi_device_path *fp,
> > +					     efi_handle_t *handle)
> > +{
> > +	efi_handle_t *fs_handles;
> > +	efi_uintn_t num;
> > +	efi_status_t ret;
> > +
> > +	ret = EFI_CALL(efi_locate_handle_buffer(
> > +					BY_PROTOCOL,
> > +					&efi_simple_file_system_protocol_guid,
> > +					NULL,
> > +					&num, &fs_handles));
> > +	if (ret != EFI_SUCCESS)
> > +		return ret;
> > +	if (!num)
> > +		return EFI_NOT_FOUND;
> > +
> > +	/* removable media first */
> > +	ret = __try_load(fs_handles, num, fp, handle, true);
> > +	if (ret == EFI_SUCCESS)
> > +		goto out;
> > +
> > +	/* fixed media */
> > +	ret = __try_load(fs_handles, num, fp, handle, false);
> > +	if (ret == EFI_SUCCESS)
> > +		goto out;
> > +
> > +out:
> > +	return ret;
> > +}
> > +
> >   /**
> >    * try_load_entry() - try to load image for boot option
> >    *
> > @@ -116,10 +201,15 @@ static efi_status_t try_load_entry(u16 n, efi_handle_t *handle,
> >   		log_debug("trying to load \"%ls\" from %pD\n", lo.label,
> >   			  lo.file_path);
> > 
> > -		file_path = expand_media_path(lo.file_path);
> > -		ret = EFI_CALL(efi_load_image(true, efi_root, file_path,
> > -					      NULL, 0, handle));
> > -		efi_free_pool(file_path);
> > +		if (EFI_DP_TYPE(lo.file_path, MEDIA_DEVICE, FILE_PATH)) {
> > +			/* file_path doesn't contain a device path */
> 
> %s/device path/device part/
> 
> In UEFI speak a file_path is a device path.
> 
> Best regards
> 
> Heinrich
> 
> > +			ret = try_load_from_short_path(lo.file_path, handle);
> > +		} else {
> > +			file_path = expand_media_path(lo.file_path);
> > +			ret = EFI_CALL(efi_load_image(true, efi_root, file_path,
> > +						      NULL, 0, handle));
> > +			efi_free_pool(file_path);
> > +		}
> >   		if (ret != EFI_SUCCESS) {
> >   			log_warning("Loading %ls '%ls' failed\n",
> >   				    varname, lo.label);