crypto: ccp - During shutdown, check SEV data pointer before using

On shutdown, each CCP device instance performs shutdown processing.
However, __sev_platform_shutdown_locked() uses the controlling psp
structure to obtain the pointer to the sev_device structure. However,
during driver initialization, it is possible that an error can be received
from the firmware that results in the sev_data pointer being cleared from
the controlling psp structure. The __sev_platform_shutdown_locked()
function does not check for this situation and will segfault.

While not common, this scenario should be accounted for. Add a check for a
NULL sev_device structure before attempting to use it.

Fixes: 5441a07a127f ("crypto: ccp - shutdown SEV firmware on kexec")
Signed-off-by: Tom Lendacky <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/ccp/sev-dev.c

···
 	struct sev_device *sev = psp_master->sev_data;
 	int ret;
 
-	if (sev->state == SEV_STATE_UNINIT)
+	if (!sev || sev->state == SEV_STATE_UNINIT)
 		return 0;
 
 	ret = __sev_do_cmd_locked(SEV_CMD_SHUTDOWN, NULL, error);