[Skiboot] [PATCH 1/2] secvar/secboot_tpm: correctly reset the control index on secboot format

[Nick Child]

On Fri, Oct 15, 2021 at 5:22 PM Eric Richter <erichte at linux.ibm.com> wrote:
>
> When the SECBOOT partition is formatted, the bank hash stored in the
> control TPM NV index must be updated to match, or else we will immediately
> fail to load the freshly formatted data at the .load_bank() step.
>
> However, while the secboot_format() function does calculate and update the
> bank hash, it only writes the new hash for bank 0. It does not update the
> value for bank 1, or set the current active bank. This works as expected if
> the active bank bit happens to be set to 0. On the other hand, if the active
> bit is set to 1, the freshly formatted bank 1 will be compared against the
> unchanged bank hash in bank 1 at the load step, therefore causing an error.
>
> This patch fixes this issue by also setting the active bit to 0 to match
> the freshly calculated hash.
>
> Signed-off-by: Eric Richter <erichte at linux.ibm.com>
Manually tested and ran with op-test, works as expected.

Tested-by: Nick Child <nick.child at ibm.com>
> ---
>  libstb/secvar/storage/secboot_tpm.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/libstb/secvar/storage/secboot_tpm.c b/libstb/secvar/storage/secboot_tpm.c
> index 129f674a..5907ff07 100644
> --- a/libstb/secvar/storage/secboot_tpm.c
> +++ b/libstb/secvar/storage/secboot_tpm.c
> @@ -127,12 +127,15 @@ static int secboot_format(void)
>                 prlog(PR_ERR, "Bank hash failed to calculate somehow\n");
>                 return rc;
>         }
> +       /* Clear bank_hash[1] anyway, to match state of PNOR */
> +       memset(tpmnv_control_image->bank_hash[1], 0x00, sizeof(tpmnv_control_image->bank_hash[1]));
> +
> +       tpmnv_control_image->active_bit = 0;
>
>         rc = tpmnv_ops.write(SECBOOT_TPMNV_CONTROL_INDEX,
> -                            tpmnv_control_image->bank_hash[0],
> -                            SHA256_DIGEST_SIZE,
> -                            offsetof(struct tpmnv_control,
> -                            bank_hash[0]));
> +                            tpmnv_control_image,
> +                            sizeof(struct tpmnv_control),
> +                            0);
>         if (rc) {
>                 prlog(PR_ERR, "Could not write fresh formatted bank hashes to CONTROL index, rc=%d\n", rc);
>                 return rc;
> --
> 2.29.2