Re: [PATCH 3/3] efi_loader: fix efi_tcg2_hash_log_extend_event() parameter check

[Heinrich Schuchardt <xypron.glpk@gmx.de>]

On 9/3/21 3:55 AM, Masahisa Kojima wrote:
> TCG EFI Protocol Specification defines that PCRIndex parameter
> passed from caller must be 0 to 23.
> TPM2_MAX_PCRS is currently used to check the range of PCRIndex,
> but TPM2_MAX_PCRS is tpm2 device dependent and may have larger value.
> This commit newly adds EFI_TCG2_MAX_PCR_INDEX macro, it is used to
> check the range of PCRIndex parameter.

In the U-Boot code we have TPM2_MAX_PCRS hard coded as 32. Can the value
be less?

>
> Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
> ---
>   include/efi_tcg2.h        | 2 ++
>   lib/efi_loader/efi_tcg2.c | 2 +-
>   2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/efi_tcg2.h b/include/efi_tcg2.h
> index 45788d55d5..b647361d44 100644
> --- a/include/efi_tcg2.h
> +++ b/include/efi_tcg2.h
> @@ -28,6 +28,8 @@
>   #define EFI_TCG2_EXTEND_ONLY 0x0000000000000001
>   #define PE_COFF_IMAGE 0x0000000000000010
>
> +#define EFI_TCG2_MAX_PCR_INDEX 23
> +
>   /* Algorithm Registry */
>   #define EFI_TCG2_BOOT_HASH_ALG_SHA1    0x00000001
>   #define EFI_TCG2_BOOT_HASH_ALG_SHA256  0x00000002
> diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
> index c4e9f61fd6..b268a02976 100644
> --- a/lib/efi_loader/efi_tcg2.c
> +++ b/lib/efi_loader/efi_tcg2.c
> @@ -958,7 +958,7 @@ efi_tcg2_hash_log_extend_event(struct efi_tcg2_protocol *this, u64 flags,
>   		goto out;
>   	}
>
> -	if (efi_tcg_event->header.pcr_index > TPM2_MAX_PCRS) {

If TPM2_MAX_PCRS were device dependent and could be less then 23 we
would need a check against both constants.

Could you, please, clarify the issue. If TPM2_MAX_PCRS is always greater
then 23, please, mention this in the commit message and perhaps add a
comment in the code here.

Best regards

Heinrich

> +	if (efi_tcg_event->header.pcr_index > EFI_TCG2_MAX_PCR_INDEX) {
>   		ret = EFI_INVALID_PARAMETER;
>   		goto out;
>   	}
>