Re: [PATCH v5 2/5] efi: Add embedded peripheral firmware support

[Hans de Goede]

Hi,

On 01-05-18 16:36, Mimi Zohar wrote:
> [Cc'ing linux-security]
>
> On Sun, 2018-04-29 at 11:35 +0200, Hans de Goede wrote:
> [...]
> > diff --git a/drivers/base/firmware_loader/fallback_efi.c b/drivers/base/firmware_loader/fallback_efi.c
> > new file mode 100644
> > index 000000000000..82ba82f48a79
> > --- /dev/null
> > +++ b/drivers/base/firmware_loader/fallback_efi.c
> > @@ -0,0 +1,51 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/efi_embedded_fw.h>
> > +#include <linux/property.h>
> > +#include <linux/security.h>
> > +#include <linux/vmalloc.h>
> > +
> > +#include "fallback.h"
> > +#include "firmware.h"
> > +
> > +int fw_get_efi_embedded_fw(struct device *dev, struct fw_priv *fw_priv,
> > +			   enum fw_opt *opt_flags, int ret)
> > +{
> > +	enum kernel_read_file_id id = READING_FIRMWARE;
>
> Please define a new kernel_read_file_id for this (eg.
> READING_FIRMWARE_EFI_EMBEDDED).

Are you sure, I wonder how useful it is to add a new
kernel_read_file_id every time a new way to get firmware
comes up?

I especially wonder about the sense in adding a new id
given that the quite old FIRMWARE_PREALLOC_BUFFER is
still not supported / checked properly by the security code.

Anyways I can add a new id if you want me to, what about
when fw_get_efi_embedded_fw is reading into a driver allocated
buffer, do you want a separate EADING_FIRMWARE_EFI_EMBEDDED_PREALLOC_BUFFER
for that ?




> > +	size_t size, max = INT_MAX;
> > +	int rc;
> > +
> > +	if (!dev)
> > +		return ret;
> > +
> > +	if (!device_property_read_bool(dev, "efi-embedded-firmware"))
> > +		return ret;
>
> Instead of calling security_kernel_post_read_file(), either in
> device_property_read_bool() or here call security_kernel_read_file().
>
> The pre read call is for deciding whether to allow this call
> independent of the firmware being loaded, whereas the post security
> call is currently being used by IMA-appraisal for verifying a
> signature. ÂThere might be other LSMs using the post hook as well. ÂAs
> there is no kernel signature associated with this firmware, use the
> security pre read_file hook.

Only the pre hook?  I believe the post-hook should still be called too,
right? So that we've hashes of all loaded firmwares in the IMA core.

Regards,

Hans


> thanks,
>
> Mimi
>
> > +
> > +	*opt_flags |= FW_OPT_NO_WARN | FW_OPT_NOCACHE | FW_OPT_NOFALLBACK;
> > +
> > +	/* Already populated data member means we're loading into a buffer */
> > +	if (fw_priv->data) {
> > +		id = READING_FIRMWARE_PREALLOC_BUFFER;
> > +		max = fw_priv->allocated_size;
> > +	}
> > +
> > +	rc = efi_get_embedded_fw(fw_priv->fw_name, &fw_priv->data, &size, max);
> > +	if (rc) {
> > +		dev_warn(dev, "Firmware %s not in EFI\n", fw_priv->fw_name);
> > +		return ret;
> > +	}
> > +
> > +	rc = security_kernel_post_read_file(NULL, fw_priv->data, size, id);
> > +	if (rc) {
> > +		if (id != READING_FIRMWARE_PREALLOC_BUFFER) {
> > +			vfree(fw_priv->data);
> > +			fw_priv->data = NULL;
> > +		}
> > +		return rc;
> > +	}
> > +
> > +	dev_dbg(dev, "using efi-embedded fw %s\n", fw_priv->fw_name);
> > +	fw_priv->size = size;
> > +	fw_state_done(fw_priv);
> > +	return 0;
> > +}