Re: [RFC PATCH v3 6/9] FWU: Add boot time checks as highlighted by the FWU specification

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hi Sughosh

[...]

> +#include <efi.h>
> +#include <efi_loader.h>
> +#include <efi_variable.h>
> +#include <fwu.h>
> +#include <fwu_mdata.h>
> +#include <malloc.h>
> +
> +#include <linux/errno.h>
> +#include <linux/types.h>
> +
> +static u8 trial_state = 0;
> +static u8 boottime_check = 0;
> +
> +static int fwu_trial_state_check(void)
> +{
> +	int ret, i;
> +	efi_status_t status;
> +	efi_uintn_t var_size;
> +	u16 trial_state_ctr;
> +	u32 nimages, active_bank, var_attributes, active_idx;
> +	struct fwu_mdata *mdata = NULL;
> +	struct fwu_image_entry *img_entry;
> +	struct fwu_image_bank_info *img_bank_info;
> +
> +	ret = fwu_get_mdata(&mdata);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = 0;
> +	nimages = CONFIG_FWU_NUM_IMAGES_PER_BANK;
> +	active_bank = mdata->active_index;
> +	img_entry = &mdata->img_entry[0];
> +	for (i = 0; i < nimages; i++) {
> +		img_bank_info = &img_entry[i].img_bank_info[active_bank];
> +		if (!img_bank_info->accepted) {
> +			trial_state = 1;
> +			break;
> +		}
> +	}
> +
> +	if (trial_state) {

That's personal preference and feel free to ignore it,  but I generally
find the code easier to read like 
if (!trial_state)
	do stuff;
	goto out;

<rest of the code follows here>

> +		var_size = (efi_uintn_t)sizeof(trial_state_ctr);
> +		log_info("System booting in Trial State\n");
> +		var_attributes = EFI_VARIABLE_NON_VOLATILE |
> +			EFI_VARIABLE_BOOTSERVICE_ACCESS |
> +			EFI_VARIABLE_RUNTIME_ACCESS;

Do we really need it with runtime access?

> +		status = efi_get_variable_int(L"TrialStateCtr",
> +					      &efi_global_variable_guid,
> +					      &var_attributes,
> +					      &var_size, &trial_state_ctr,
> +					      NULL);
> +		if (status != EFI_SUCCESS) {
> +			log_err("Unable to read TrialStateCtr variable\n");
> +			ret = -1;
> +			goto out;
> +		}
> +
> +		++trial_state_ctr;
> +		if (trial_state_ctr > CONFIG_FWU_TRIAL_STATE_CNT) {
> +			log_info("Trial State count exceeded. Revert back to previous_active_index\n");
> +			active_idx = mdata->active_index;
> +			ret = fwu_revert_boot_index();
> +			if (ret < 0) {
> +				log_err("Unable to revert active_index\n");
> +				goto out;
> +			}
> +
> +			trial_state_ctr = 0;
> +			status = efi_set_variable_int(L"TrialStateCtr",
> +						      &efi_global_variable_guid,
> +						      var_attributes,
> +						      0,
> +						      &trial_state_ctr, false);
> +			if (status != EFI_SUCCESS) {
> +				log_err("Unable to clear TrialStateCtr variable\n");
> +				ret = -1;
> +				goto out;
> +			}
> +		} else {
> +			status = efi_set_variable_int(L"TrialStateCtr",
> +						      &efi_global_variable_guid,
> +						      var_attributes,
> +						      var_size,
> +						      &trial_state_ctr, false);
> +			if (status != EFI_SUCCESS) {
> +				log_err("Unable to increment TrialStateCtr variable\n");
> +				ret = -1;
> +				goto out;
> +			} else {
> +				ret = 0;
> +			}
> +		}
> +	} else {
> +		trial_state_ctr = 0;
> +		ret = 0;
> +		status = efi_set_variable_int(L"TrialStateCtr",
> +					      &efi_global_variable_guid,
> +					      0,
> +					      0, &trial_state_ctr,
> +					      NULL);

We can't completely ignore the failed setvariable here, as it will affect
the entire code path from that point onwards.  Any checks after an update
will fail since the variable wont be there.


> +	}
> +
> +out:
> +	free(mdata);
> +	return ret;
> +}
> +
> +u8 fwu_update_checks_pass(void)
> +{
> +	return !trial_state && boottime_check;
> +}
> +
> +int fwu_boottime_checks(void)
> +{
> +	int ret;
> +	u32 boot_idx, active_idx;
> +
> +	ret = fwu_mdata_check();
> +	if (ret < 0) {
> +		boottime_check = 0;
> +		return 0;
> +	}
> +
> +	/*
> +	 * Get the Boot Index, i.e. the bank from
> +	 * which the platform has booted. This value
> +	 * gets passed from the ealier stage bootloader
> +	 * which booted u-boot, e.g. tf-a. If the
> +	 * boot index is not the same as the
> +	 * active_index read from the FWU metadata,
> +	 * update the active_index.
> +	 */
> +	fwu_plat_get_bootidx(&boot_idx);
> +	if (boot_idx >= CONFIG_FWU_NUM_BANKS) {
> +		log_err("Received incorrect value of boot_index\n");
> +		boottime_check = 0;
> +		return 0;
> +	}
> +
> +	ret = fwu_get_active_index(&active_idx);
> +	if (ret < 0) {
> +		log_err("Unable to read active_index\n");
> +		boottime_check = 0;
> +		return 0;
> +	}
> +
> +	if (boot_idx != active_idx) {
> +		log_info("Boot idx %u is not matching active idx %u, changing active_idx\n",
> +			 boot_idx, active_idx);
> +		ret = fwu_update_active_index(boot_idx);
> +		if (ret < 0)
> +			boottime_check = 0;
> +		else
> +			boottime_check = 1;
> +
> +		return 0;
> +	}
> +
> +	ret = fwu_trial_state_check();
> +	if (ret < 0)
> +		boottime_check = 0;
> +	else
> +		boottime_check = 1;
> +
> +	return 0;
> +}
> -- 

cheers
/Ilias
> 2.17.1
>