linux-kernel - Re: [PATCH 6/6] libstub,tpm: do not ignore failure case when reading final event log

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Message-ID: <CAMj1kXHRkDCnUCjBR17jSCwceGT8fyE_WdERmVpYY7c6eBsgFA@mail.gmail.com>
Date: Fri, 13 Sep 2024 17:25:27 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Gregory Price <gourry@...rry.net>
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org, leitao@...ian.org, 
	usamaarif642@...il.com, sathyanarayanan.kuppuswamy@...ux.intel.com, 
	ilias.apalodimas@...aro.org
Subject: Re: [PATCH 6/6] libstub,tpm: do not ignore failure case when reading
 final event log

On Fri, 6 Sept 2024 at 22:28, Gregory Price <gourry@...rry.net> wrote:
>
> Current code fails to check for an error case when reading events from
> final event log to calculate offsets.  Check the error case, report the
> error, and break early because all subsequent calls will also fail.
>
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>  drivers/firmware/efi/libstub/tpm.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/tpm.c b/drivers/firmware/efi/libstub/tpm.c
> index 4f9f0e049a7a..c71b0d3e66d2 100644
> --- a/drivers/firmware/efi/libstub/tpm.c
> +++ b/drivers/firmware/efi/libstub/tpm.c
> @@ -124,6 +124,10 @@ static void efi_retrieve_tcg2_eventlog(int version, efi_physical_addr_t log_loca
>                         event_size = __calc_tpm2_event_size(header,
>                                                    (void *)(long)log_location,
>                                                    false);
> +                       if (!event_size) {
> +                               efi_err("Invalid TPM Final Event Log Entry\n");
> +                               break;
> +                       }

I don't object to this in principle, the only problem is that these
log prints are not recorded anywhere: they are printed to the EFI boot
console by the EFI stub, which may not even be visible, and is
definitely not captured by the kernel logging routines.