linux-kernel - Re: [tpmdd-devel] [PATCH v2 2/3] efi: call get_event

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Date:   Thu, 14 Sep 2017 12:24:29 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thiebaud Weksteen <tweek@...gle.com>, linux-efi@...r.kernel.org
Cc:     ard.biesheuvel@...aro.org, matt@...eblueprint.co.uk,
        linux-kernel@...r.kernel.org, mjg59@...gle.com,
        jgunthorpe@...idianresearch.com, tpmdd-devel@...ts.sourceforge.net,
        jarkko.sakkinen@...ux.intel.com, Peter Jones <pjones@...hat.com>
Subject: Re: [tpmdd-devel] [PATCH v2 2/3] efi: call get_event_log before
 ExitBootServices

On 09/11/2017 12:00 PM, Thiebaud Weksteen via tpmdd-devel wrote:
> With TPM 2.0 specification, the event logs may only be accessible by
> calling an EFI Boot Service. Modify the EFI stub to copy the log area to
> a new Linux-specific EFI configuration table so it remains accessible
> once booted.
> 
> When calling this service, it is possible to specify the expected format
> of the logs: TPM 1.2 (SHA1) or TPM 2.0 ("Crypto Agile"). For now, only the
> first format is retrieved.
> 
> Signed-off-by: Thiebaud Weksteen <tweek@...gle.com>
> ---

[snip]

> +void efi_retrieve_tpm2_eventlog_1_2(efi_system_table_t *sys_table_arg)
> +{

[snip]

> +
> +	/* Allocate space for the logs and copy them. */
> +	status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
> +				sizeof(*log_tbl) + log_size,
> +				(void **) &log_tbl);
> +
> +	if (status != EFI_SUCCESS) {
> +		efi_printk(sys_table_arg,
> +			   "Unable to allocate memory for event log\n");
> +		return;
> +	}

If this fails or any previous error that will prevent the event log table + logs
to be allocated, shouldn't tpm_read_log_efi() be notified somehow? Since AFAICT
it will still try to access them even if the EFI allocate_pool did not succeed.

> + */
> +int __init efi_tpm_eventlog_init(void)
> +{
> +	struct linux_efi_tpm_eventlog *tbl;
> +	unsigned int tbl_size;
> +

The functions efi_retrieve_tpm2_eventlog_1_2() and tpm_read_log_efi() are using
log_tbl as variable name, so I would use it here too for consistency.

> +	if (efi.tpm_log == EFI_INVALID_TABLE_ADDR)
> +		return 0;
> +
> +	tbl = early_memremap(efi.tpm_log, sizeof(*tbl));
> +	if (!tbl) {
> +		pr_err("Failed to map TPM Event Log table @ 0x%lx\n",
> +			efi.tpm_log);
> +		return -ENOMEM;
> +	}
> +

Same question than before, if this fails then the table + logs memory won't be
reserved but tpm_read_log_efi() will still try to access it. I'm not sure what
is the correct way to notify though, maybe setting efi.tpm_log to 0 and then in
tpm_read_log_efi() check efi.tpm_log for 0 or EFI_INVALID_TABLE_ADDR instead?

> +	tbl_size = sizeof(*tbl) + tbl->size;
> +	memblock_reserve(efi.tpm_log, tbl_size);
> +	early_memunmap(tbl, sizeof(*tbl));
> +	return 0;

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat