mirror of https://github.com/ipxe/ipxe.git
[rng] Add RTC-based entropy source
The RTC-based entropy source uses the nanosecond-scale CPU TSC to measure the time between two 1kHz interrupts generated by the CMOS RTC. In a physical machine these clocks are driven from independent crystals, resulting in some observable clock drift. In a virtual machine, the CMOS RTC is typically emulated using host-OS constructions such as SIGALRM. Signed-off-by: Michael Brown <mcb30@ipxe.org>pull/5/merge
Michael Brown
parent
5d2e65c60f
commit
05719804b9
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@ -9,4 +9,6 @@
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FILE_LICENCE ( GPL2_OR_LATER );
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#include <ipxe/rtc_entropy.h>
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#endif /* _BITS_ENTROPY_H */
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@ -0,0 +1,62 @@
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#ifndef _IPXE_RTC_ENTROPY_H
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#define _IPXE_RTC_ENTROPY_H
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/** @file
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*
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* RTC-based entropy source
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*
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*/
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FILE_LICENCE ( GPL2_OR_LATER );
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#include <stdint.h>
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#ifdef ENTROPY_RTC
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#define ENTROPY_PREFIX_rtc
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#else
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#define ENTROPY_PREFIX_rtc __rtc_
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#endif
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/**
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* min-entropy per sample
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*
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* @ret min_entropy min-entropy of each sample
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*/
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static inline __always_inline double
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ENTROPY_INLINE ( rtc, min_entropy_per_sample ) ( void ) {
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/* The min-entropy has been measured on several platforms
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* using the entropy_sample test code. Modelling the samples
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* as independent, and using a confidence level of 99.99%, the
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* measurements were as follows:
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*
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* qemu-kvm : 7.38 bits
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* VMware : 7.46 bits
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* Physical hardware : 2.67 bits
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*
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* We choose the lowest of these (2.67 bits) and apply a 50%
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* safety margin to allow for some potential non-independence
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* of samples.
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*/
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return 1.3;
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}
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extern uint8_t rtc_sample ( void );
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/**
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* Get noise sample
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*
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* @ret noise Noise sample
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* @ret rc Return status code
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*/
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static inline __always_inline int
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ENTROPY_INLINE ( rtc, get_noise ) ( noise_sample_t *noise ) {
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/* Get sample */
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*noise = rtc_sample();
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/* Always successful */
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return 0;
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}
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#endif /* _IPXE_RTC_ENTROPY_H */
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@ -0,0 +1,233 @@
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/*
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* Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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FILE_LICENCE ( GPL2_OR_LATER );
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/** @file
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*
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* RTC-based entropy source
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*
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* The CMOS/RTC registers are documented (with varying degrees of
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* accuracy and consistency) at
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*
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* http://www.nondot.org/sabre/os/files/MiscHW/RealtimeClockFAQ.txt
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* http://wiki.osdev.org/RTC
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* http://wiki.osdev.org/CMOS
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*/
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#include <stdint.h>
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#include <string.h>
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#include <biosint.h>
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#include <pic8259.h>
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#include <ipxe/entropy.h>
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/** RTC IRQ */
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#define RTC_IRQ 8
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/** RTC interrupt vector */
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#define RTC_INT IRQ_INT ( RTC_IRQ )
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/** CMOS/RTC address (and NMI) register */
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#define CMOS_ADDRESS 0x70
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/** NMI disable bit */
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#define CMOS_DISABLE_NMI 0x80
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/** CMOS/RTC data register */
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#define CMOS_DATA 0x71
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/** RTC status register A */
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#define RTC_STATUS_A 0x0a
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/** RTC status register B */
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#define RTC_STATUS_B 0x0b
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/** RTC Periodic Interrupt Enabled bit */
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#define RTC_STATUS_B_PIE 0x40
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/** RTC status register C */
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#define RTC_STATUS_C 0x0c
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/** RTC status register D */
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#define RTC_STATUS_D 0x0d
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/** CMOS default address */
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#define CMOS_DEFAULT_ADDRESS RTC_STATUS_D
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/** RTC "interrupt triggered" flag */
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static uint8_t __text16 ( rtc_flag );
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#define rtc_flag __use_text16 ( rtc_flag )
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/** RTC interrupt handler */
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extern void rtc_isr ( void );
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/** Previous RTC interrupt handler */
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static struct segoff rtc_old_handler;
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/**
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* Hook RTC interrupt handler
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*
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*/
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static void rtc_hook_isr ( void ) {
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/* RTC interrupt handler */
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__asm__ __volatile__ (
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TEXT16_CODE ( "\nrtc_isr:\n\t"
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/* Preserve registers */
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"pushw %%ax\n\t"
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/* Set "interrupt triggered" flag */
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"cs movb $0x01, %c0\n\t"
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/* Read RTC status register C to
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* acknowledge interrupt
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*/
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"movb %3, %%al\n\t"
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"outb %%al, %1\n\t"
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"inb %2\n\t"
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/* Send EOI */
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"movb $0x20, %%al\n\t"
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"outb %%al, $0xa0\n\t"
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"outb %%al, $0x20\n\t"
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/* Restore registers and return */
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"popw %%ax\n\t"
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"iret\n\t" )
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:
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: "p" ( __from_text16 ( &rtc_flag ) ),
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"i" ( CMOS_ADDRESS ), "i" ( CMOS_DATA ),
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"i" ( RTC_STATUS_C ) );
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hook_bios_interrupt ( RTC_INT, ( unsigned int ) rtc_isr,
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&rtc_old_handler );
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}
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/**
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* Unhook RTC interrupt handler
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*
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*/
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static void rtc_unhook_isr ( void ) {
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int rc;
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rc = unhook_bios_interrupt ( RTC_INT, ( unsigned int ) rtc_isr,
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&rtc_old_handler );
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assert ( rc == 0 ); /* Should always be able to unhook */
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}
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/**
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* Enable RTC interrupts
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*
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*/
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static void rtc_enable_int ( void ) {
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uint8_t status_b;
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/* Set Periodic Interrupt Enable bit in status register B */
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outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
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status_b = inb ( CMOS_DATA );
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outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
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outb ( ( status_b | RTC_STATUS_B_PIE ), CMOS_DATA );
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/* Re-enable NMI and reset to default address */
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outb ( CMOS_DEFAULT_ADDRESS, CMOS_ADDRESS );
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inb ( CMOS_DATA ); /* Discard; may be needed on some platforms */
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}
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/**
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* Disable RTC interrupts
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*
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*/
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static void rtc_disable_int ( void ) {
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uint8_t status_b;
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/* Clear Periodic Interrupt Enable bit in status register B */
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outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
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status_b = inb ( CMOS_DATA );
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outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
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outb ( ( status_b & ~RTC_STATUS_B_PIE ), CMOS_DATA );
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/* Re-enable NMI and reset to default address */
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outb ( CMOS_DEFAULT_ADDRESS, CMOS_ADDRESS );
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inb ( CMOS_DATA ); /* Discard; may be needed on some platforms */
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}
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/**
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* Enable entropy gathering
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*
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*/
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static void rtc_entropy_enable ( void ) {
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rtc_hook_isr();
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enable_irq ( RTC_IRQ );
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rtc_enable_int();
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}
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/**
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* Disable entropy gathering
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*
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*/
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static void rtc_entropy_disable ( void ) {
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rtc_disable_int();
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disable_irq ( RTC_IRQ );
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rtc_unhook_isr();
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}
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/**
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* Measure a single RTC tick
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*
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* @ret delta Length of RTC tick (in TSC units)
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*/
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uint8_t rtc_sample ( void ) {
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uint32_t before;
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uint32_t after;
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uint32_t temp;
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__asm__ __volatile__ (
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REAL_CODE ( /* Enable interrupts */
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"sti\n\t"
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/* Wait for RTC interrupt */
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"cs movb %b2, %c4\n\t"
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"\n1:\n\t"
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"cs xchgb %b2, %c4\n\t" /* Serialize */
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"testb %b2, %b2\n\t"
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"jz 1b\n\t"
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/* Read "before" TSC */
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"rdtsc\n\t"
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/* Store "before" TSC on stack */
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"pushl %0\n\t"
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/* Wait for another RTC interrupt */
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"xorb %b2, %b2\n\t"
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"cs movb %b2, %c4\n\t"
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"\n1:\n\t"
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"cs xchgb %b2, %c4\n\t" /* Serialize */
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"testb %b2, %b2\n\t"
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"jz 1b\n\t"
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/* Read "after" TSC */
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"rdtsc\n\t"
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/* Retrieve "before" TSC on stack */
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"popl %1\n\t"
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/* Disable interrupts */
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"cli\n\t"
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)
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: "=a" ( after ), "=d" ( before ), "=q" ( temp )
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: "2" ( 0 ), "p" ( __from_text16 ( &rtc_flag ) ) );
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return ( after - before );
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}
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PROVIDE_ENTROPY_INLINE ( rtc, min_entropy_per_sample );
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PROVIDE_ENTROPY ( rtc, entropy_enable, rtc_entropy_enable );
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PROVIDE_ENTROPY ( rtc, entropy_disable, rtc_entropy_disable );
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PROVIDE_ENTROPY_INLINE ( rtc, get_noise );
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@ -18,7 +18,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
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#define UMALLOC_MEMTOP
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#define SMBIOS_PCBIOS
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#define SANBOOT_PCBIOS
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#define ENTROPY_NULL
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#define ENTROPY_RTC
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#define IMAGE_ELF /* ELF image support */
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#define IMAGE_MULTIBOOT /* MultiBoot image support */
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