Re: [PATCH v7 4/5] efi: Load efi_secret module if EFI secret area is populated

Gerd Hoffmann
2022-02-02T14:31:43Z

On Wed, Feb 02, 2022 at 01:08:43PM +0200, Dov Murik wrote:
>
>
> On 02/02/2022 10:47, Gerd Hoffmann wrote:
> > On Tue, Feb 01, 2022 at 12:44:12PM +0000, Dov Murik wrote:
> >> If the efi_secret module is built, register a late_initcall in the EFI
> >> driver which checks whether the EFI secret area is available and
> >> populated, and then requests to load the efi_secret module.
> >
> >> + area = memremap(efi.coco_secret, sizeof(*area), MEMREMAP_WB);
> >> + if (!area) {
> >> + pr_err("Failed to map confidential computing secret area descriptor\n");
> >> + return -ENOMEM;
> >> + }
> >> + if (!area->base_pa || area->size < sizeof(*header_guid))
> >> + goto unmap_desc;
> >> +
> >> + header_guid = (void __force *)ioremap_encrypted(area->base_pa, sizeof(*header_guid));
> >> + if (!header_guid) {
> >> + pr_err("Failed to map secret area\n");
> >> + ret = -ENOMEM;
> >> + goto unmap_desc;
> >> + }
> >> + if (efi_guidcmp(*header_guid, EFI_SECRET_TABLE_HEADER_GUID))
> >> + goto unmap_encrypted;
> >
> > Why these sanity checks are here and not in the efi_secret module?
>
> The same checks indeed appear in the efi_secret module (see in patch 3:
> efi_secret_map_area() and the beginning of efi_secret_securityfs_setup()).
>
> However, in the efi_secret module, the checks are noisy, because they
> expect the secret area to be populated. For example:
>
> + if (efi.coco_secret == EFI_INVALID_TABLE_ADDR) {
> + pr_err("Secret area address is not available\n");
> + return -EINVAL;
> + }

Note I explicitly excluded that check ;)

Checking whenever efi.coco_secret looks valid and only try load
efi_secret if that is the case (and otherwise stay silent) makes
perfect sense. The other checks should be dropped IMHO.

> Another approach could be to just try to load the module anyway, and
> the module will fail (silently? noisily?) if there's no designated
> secret area or it's not populated. I feel that will be harder to
> understand what's going on.

I think the module should fail noisily. See above for autoload. In
case the module is loaded (either manually by the admin, or because
efi.coco_secret != EFI_INVALID_TABLE_ADDR) and it can't actually load
the secrets we want know why ...

take care,
Gerd