== Background == ENCLS[EUPDATESVN] is a new SGX instruction [1] which allows enclave attestation to include information about updated microcode SVN without a reboot. Before an EUPDATESVN operation can be successful, all SGX memory (aka. EPC) must be marked as “unused” in the SGX hardware metadata (aka.EPCM). This requirement ensures that no compromised enclave can survive the EUPDATESVN procedure and provides an opportunity to generate new cryptographic assets.
== Solution == Attempt to execute ENCLS[EUPDATESVN] every time the first file descriptor is obtained via sgx_(vepc_)open(). In the most common case the microcode SVN is already up-to-date, and the operation succeeds without updating SVN. Note: while in such cases the underlying crypto assets are regenrated, it does not affect enclaves' visible keys obtained via EGETKEY instruction. If it fails with any other error code than SGX_INSUFFICIENT_ENTROPY, this is considered unexpected and the *open() returns an error. This should not happen in practice. On contrary, SGX_INSUFFICIENT_ENTROPY might happen due to a pressure on the system's DRNG (RDSEED) and therefore the *open() can be safely retried to allow normal enclave operation. [1] Runtime Microcode Updates with Intel Software Guard Extensions, https://cdrdv2.intel.com/v1/dl/getContent/648682 Reviewed-by: Jarkko Sakkinen <jar...@kernel.org> Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> --- arch/x86/kernel/cpu/sgx/main.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c index 829bcba77d41..39bff3488350 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -934,7 +934,7 @@ static int sgx_usage_count; * entropy in RNG * %-EIO: - Unexpected error, retries are not advisable */ -static int __maybe_unused sgx_update_svn(void) +static int sgx_update_svn(void) { int ret; @@ -992,14 +992,22 @@ static int __maybe_unused sgx_update_svn(void) return -EIO; } +/* Mutex to ensure no concurrent EPC accesses during EUPDATESVN */ +static DEFINE_MUTEX(sgx_svn_lock); + int sgx_inc_usage_count(void) { + guard(mutex)(&sgx_svn_lock); + + if (sgx_usage_count++ == 0) + return sgx_update_svn(); + return 0; } void sgx_dec_usage_count(void) { - return; + sgx_usage_count--; } static int __init sgx_init(void) -- 2.45.2
