diff options
Diffstat (limited to 'src/arch/x86/interface/pcbios/rtc_entropy.c')
| -rw-r--r-- | src/arch/x86/interface/pcbios/rtc_entropy.c | 38 |
1 files changed, 30 insertions, 8 deletions
diff --git a/src/arch/x86/interface/pcbios/rtc_entropy.c b/src/arch/x86/interface/pcbios/rtc_entropy.c index c400d8a..8f47ff6 100644 --- a/src/arch/x86/interface/pcbios/rtc_entropy.c +++ b/src/arch/x86/interface/pcbios/rtc_entropy.c @@ -39,6 +39,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); #include <ipxe/cpuid.h> #include <ipxe/entropy.h> +struct entropy_source rtc_entropy __entropy_source ( ENTROPY_NORMAL ); + /** Maximum time to wait for an RTC interrupt, in milliseconds */ #define RTC_MAX_WAIT_MS 100 @@ -203,6 +205,21 @@ static int rtc_entropy_enable ( void ) { if ( ( rc = rtc_entropy_check() ) != 0 ) goto err_check; + /* The min-entropy has been measured on several platforms + * using the entropy_sample test code. Modelling the samples + * as independent, and using a confidence level of 99.99%, the + * measurements were as follows: + * + * qemu-kvm : 7.38 bits + * VMware : 7.46 bits + * Physical hardware : 2.67 bits + * + * We choose the lowest of these (2.67 bits) and apply a 50% + * safety margin to allow for some potential non-independence + * of samples. + */ + entropy_init ( &rtc_entropy, MIN_ENTROPY ( 1.3 ) ); + return 0; err_check: @@ -226,11 +243,12 @@ static void rtc_entropy_disable ( void ) { } /** - * Measure a single RTC tick + * Get noise sample * - * @ret delta Length of RTC tick (in TSC units) + * @ret noise Noise sample + * @ret rc Return status code */ -uint8_t rtc_sample ( void ) { +static int rtc_get_noise ( noise_sample_t *noise ) { uint32_t before; uint32_t after; uint32_t temp; @@ -265,10 +283,14 @@ uint8_t rtc_sample ( void ) { : "=a" ( after ), "=d" ( before ), "=Q" ( temp ) : "2" ( 0 ) ); - return ( after - before ); + *noise = ( after - before ); + return 0; } -PROVIDE_ENTROPY_INLINE ( rtc, min_entropy_per_sample ); -PROVIDE_ENTROPY ( rtc, entropy_enable, rtc_entropy_enable ); -PROVIDE_ENTROPY ( rtc, entropy_disable, rtc_entropy_disable ); -PROVIDE_ENTROPY_INLINE ( rtc, get_noise ); +/** RTC entropy source */ +struct entropy_source rtc_entropy __entropy_source ( ENTROPY_NORMAL ) = { + .name = "rtc", + .enable = rtc_entropy_enable, + .disable = rtc_entropy_disable, + .get_noise = rtc_get_noise, +}; |