On Thu, Aug 26, 2021 at 03:48:02PM +0200, Heinrich Schuchardt wrote:
> The UEFI specification requires that the signature database may only be
> stored in tamper-resistant storage. So these variable may not be read
> from an unsigned file.
I don't have a strong opinion here, but it seems to be too restrictive.
Nobody expects that file-based variable implementation is *safe*.
Leave it as it is so that people can easily experiment secure boot.
-Takahiro Akashi
> Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
> ---
> v2:
> no change
> ---
> include/efi_variable.h | 5 +++-
> lib/efi_loader/efi_var_common.c | 2 --
> lib/efi_loader/efi_var_file.c | 41 ++++++++++++++++++++-------------
> lib/efi_loader/efi_variable.c | 2 +-
> 4 files changed, 30 insertions(+), 20 deletions(-)
>
> diff --git a/include/efi_variable.h b/include/efi_variable.h
> index 4623a64142..2d97655e1f 100644
> --- a/include/efi_variable.h
> +++ b/include/efi_variable.h
> @@ -161,10 +161,13 @@ efi_status_t __maybe_unused efi_var_collect(struct
> efi_var_file **bufp, loff_t *
> /**
> * efi_var_restore() - restore EFI variables from buffer
> *
> + * Only if @safe is set secure boot related variables will be restored.
> + *
> * @buf: buffer
> + * @safe: restoring from tamper-resistant storage
> * Return: status code
> */
> -efi_status_t efi_var_restore(struct efi_var_file *buf);
> +efi_status_t efi_var_restore(struct efi_var_file *buf, bool safe);
>
> /**
> * efi_var_from_file() - read variables from file
> diff --git a/lib/efi_loader/efi_var_common.c b/lib/efi_loader/efi_var_common.c
> index cf7afecd60..b0c5b672c5 100644
> --- a/lib/efi_loader/efi_var_common.c
> +++ b/lib/efi_loader/efi_var_common.c
> @@ -32,10 +32,8 @@ static const struct efi_auth_var_name_type name_type[] = {
> {u"KEK", &efi_global_variable_guid, EFI_AUTH_VAR_KEK},
> {u"db", &efi_guid_image_security_database, EFI_AUTH_VAR_DB},
> {u"dbx", &efi_guid_image_security_database, EFI_AUTH_VAR_DBX},
> - /* not used yet
> {u"dbt", &efi_guid_image_security_database, EFI_AUTH_VAR_DBT},
> {u"dbr", &efi_guid_image_security_database, EFI_AUTH_VAR_DBR},
> - */
> };
>
> static bool efi_secure_boot;
> diff --git a/lib/efi_loader/efi_var_file.c b/lib/efi_loader/efi_var_file.c
> index de076b8cbc..c7c6805ed0 100644
> --- a/lib/efi_loader/efi_var_file.c
> +++ b/lib/efi_loader/efi_var_file.c
> @@ -148,9 +148,10 @@ error:
> #endif
> }
>
> -efi_status_t efi_var_restore(struct efi_var_file *buf)
> +efi_status_t efi_var_restore(struct efi_var_file *buf, bool safe)
> {
> struct efi_var_entry *var, *last_var;
> + u16 *data;
> efi_status_t ret;
>
> if (buf->reserved || buf->magic != EFI_VAR_FILE_MAGIC ||
> @@ -160,21 +161,29 @@ efi_status_t efi_var_restore(struct efi_var_file *buf)
> return EFI_INVALID_PARAMETER;
> }
>
> - var = buf->var;
> last_var = (struct efi_var_entry *)((u8 *)buf + buf->length);
> - while (var < last_var) {
> - u16 *data = var->name + u16_strlen(var->name) + 1;
> -
> - if (var->attr & EFI_VARIABLE_NON_VOLATILE && var->length) {
> - ret = efi_var_mem_ins(var->name, &var->guid, var->attr,
> - var->length, data, 0, NULL,
> - var->time);
> - if (ret != EFI_SUCCESS)
> - log_err("Failed to set EFI variable %ls\n",
> - var->name);
> - }
> - var = (struct efi_var_entry *)
> - ALIGN((uintptr_t)data + var->length, 8);
> + for (var = buf->var; var < last_var;
> + var = (struct efi_var_entry *)
> + ALIGN((uintptr_t)data + var->length, 8)) {
> +
> + data = var->name + u16_strlen(var->name) + 1;
> +
> + /*
> + * Secure boot related and non-volatile variables shall only be
> + * restored from U-Boot's preseed.
> + */
> + if (!safe &&
> + (efi_auth_var_get_type(var->name, &var->guid) !=
> + EFI_AUTH_VAR_NONE ||
> + !(var->attr & EFI_VARIABLE_NON_VOLATILE)))
> + continue;
> + if (!var->length)
> + continue;
> + ret = efi_var_mem_ins(var->name, &var->guid, var->attr,
> + var->length, data, 0, NULL,
> + var->time);
> + if (ret != EFI_SUCCESS)
> + log_err("Failed to set EFI variable %ls\n", var->name);
> }
> return EFI_SUCCESS;
> }
> @@ -213,7 +222,7 @@ efi_status_t efi_var_from_file(void)
> log_err("Failed to load EFI variables\n");
> goto error;
> }
> - if (buf->length != len || efi_var_restore(buf) != EFI_SUCCESS)
> + if (buf->length != len || efi_var_restore(buf, false) != EFI_SUCCESS)
> log_err("Invalid EFI variables file\n");
> error:
> free(buf);
> diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
> index ba0874e9e7..a7d305ffbc 100644
> --- a/lib/efi_loader/efi_variable.c
> +++ b/lib/efi_loader/efi_variable.c
> @@ -426,7 +426,7 @@ efi_status_t efi_init_variables(void)
>
> if (IS_ENABLED(CONFIG_EFI_VARIABLES_PRESEED)) {
> ret = efi_var_restore((struct efi_var_file *)
> - __efi_var_file_begin);
> + __efi_var_file_begin, true);
> if (ret != EFI_SUCCESS)
> log_err("Invalid EFI variable seed\n");
> }
> --
> 2.30.2
>
