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opengnsys_ipxe/src/arch/x86/interface/pcbios/rtc_entropy.c

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/*
* Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** @file
*
* RTC-based entropy source
*
*/
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <biosint.h>
#include <pic8259.h>
#include <rtc.h>
#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
/** Number of RTC interrupts to check for */
#define RTC_CHECK_COUNT 3
/** RTC interrupt handler */
extern void rtc_isr ( void );
/** Previous RTC interrupt handler */
static struct segoff rtc_old_handler;
/** Previous RTC interrupt enabled state */
static uint8_t rtc_irq_enabled;
/** Previous RTC periodic interrupt enabled state */
static uint8_t rtc_int_enabled;
/** Flag set by RTC interrupt handler */
extern volatile uint8_t __text16 ( rtc_flag );
#define rtc_flag __use_text16 ( rtc_flag )
/**
* Hook RTC interrupt handler
*
*/
static void rtc_hook_isr ( void ) {
/* RTC interrupt handler */
__asm__ __volatile__ (
TEXT16_CODE ( "\nrtc_isr:\n\t"
/* Preserve registers */
"pushw %%ax\n\t"
/* Set "interrupt triggered" flag */
"movb $0x01, %%cs:rtc_flag\n\t"
/* Read RTC status register C to
* acknowledge interrupt
*/
"movb %2, %%al\n\t"
"outb %%al, %0\n\t"
"inb %1\n\t"
/* Send EOI */
"movb $0x20, %%al\n\t"
"outb %%al, $0xa0\n\t"
"outb %%al, $0x20\n\t"
/* Restore registers and return */
"popw %%ax\n\t"
"iret\n\t"
"\nrtc_flag:\n\t"
".byte 0\n\t" )
:
: "i" ( CMOS_ADDRESS ), "i" ( CMOS_DATA ),
"i" ( RTC_STATUS_C ) );
hook_bios_interrupt ( RTC_INT, ( intptr_t ) rtc_isr, &rtc_old_handler );
}
/**
* Unhook RTC interrupt handler
*
*/
static void rtc_unhook_isr ( void ) {
int rc;
rc = unhook_bios_interrupt ( RTC_INT, ( intptr_t ) rtc_isr,
&rtc_old_handler );
assert ( rc == 0 ); /* Should always be able to unhook */
}
/**
* Enable RTC interrupts
*
* @ret enabled Periodic interrupt was previously enabled
*/
static int rtc_enable_int ( void ) {
uint8_t status_b;
/* Clear any stale pending interrupts via status register C */
outb ( ( RTC_STATUS_C | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
inb ( CMOS_DATA );
/* Set Periodic Interrupt Enable bit in status register B */
outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
status_b = inb ( CMOS_DATA );
outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
outb ( ( status_b | RTC_STATUS_B_PIE ), CMOS_DATA );
/* Re-enable NMI and reset to default address */
outb ( CMOS_DEFAULT_ADDRESS, CMOS_ADDRESS );
inb ( CMOS_DATA ); /* Discard; may be needed on some platforms */
/* Return previous state */
return ( status_b & RTC_STATUS_B_PIE );
}
/**
* Disable RTC interrupts
*
*/
static void rtc_disable_int ( void ) {
uint8_t status_b;
/* Clear Periodic Interrupt Enable bit in status register B */
outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
status_b = inb ( CMOS_DATA );
outb ( ( RTC_STATUS_B | CMOS_DISABLE_NMI ), CMOS_ADDRESS );
outb ( ( status_b & ~RTC_STATUS_B_PIE ), CMOS_DATA );
/* Re-enable NMI and reset to default address */
outb ( CMOS_DEFAULT_ADDRESS, CMOS_ADDRESS );
inb ( CMOS_DATA ); /* Discard; may be needed on some platforms */
}
/**
* Check that entropy gathering is functional
*
* @ret rc Return status code
*/
static int rtc_entropy_check ( void ) {
unsigned int count = 0;
unsigned int i;
/* Check that RTC interrupts are working */
rtc_flag = 0;
for ( i = 0 ; i < RTC_MAX_WAIT_MS ; i++ ) {
/* Allow interrupts to occur */
__asm__ __volatile__ ( "sti\n\t"
"nop\n\t"
"nop\n\t"
"cli\n\t" );
/* Check for RTC interrupt flag */
if ( rtc_flag ) {
rtc_flag = 0;
if ( ++count >= RTC_CHECK_COUNT )
return 0;
}
/* Delay */
mdelay ( 1 );
}
DBGC ( &rtc_flag, "RTC timed out waiting for interrupt %d/%d\n",
( count + 1 ), RTC_CHECK_COUNT );
return -ETIMEDOUT;
}
/**
* Enable entropy gathering
*
* @ret rc Return status code
*/
static int rtc_entropy_enable ( void ) {
struct x86_features features;
int rc;
/* Check that TSC is supported */
x86_features ( &features );
if ( ! ( features.intel.edx & CPUID_FEATURES_INTEL_EDX_TSC ) ) {
DBGC ( &rtc_flag, "RTC has no TSC\n" );
rc = -ENOTSUP;
goto err_no_tsc;
}
/* Hook ISR and enable RTC interrupts */
rtc_hook_isr();
rtc_irq_enabled = enable_irq ( RTC_IRQ );
rtc_int_enabled = rtc_enable_int();
DBGC ( &rtc_flag, "RTC had IRQ%d %sabled, interrupt %sabled\n",
RTC_IRQ, ( rtc_irq_enabled ? "en" : "dis" ),
( rtc_int_enabled ? "en" : "dis" ) );
/* Check that RTC interrupts are working */
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:
if ( ! rtc_int_enabled )
rtc_disable_int();
if ( ! rtc_irq_enabled )
disable_irq ( RTC_IRQ );
rtc_unhook_isr();
err_no_tsc:
return rc;
}
/**
* Disable entropy gathering
*
*/
static void rtc_entropy_disable ( void ) {
/* Restore RTC interrupt state and unhook ISR */
if ( ! rtc_int_enabled )
rtc_disable_int();
if ( ! rtc_irq_enabled )
disable_irq ( RTC_IRQ );
rtc_unhook_isr();
}
/**
* Get noise sample
*
* @ret noise Noise sample
* @ret rc Return status code
*/
static int rtc_get_noise ( noise_sample_t *noise ) {
uint32_t before;
uint32_t after;
uint32_t temp;
__asm__ __volatile__ (
REAL_CODE ( /* Enable interrupts */
"sti\n\t"
/* Wait for RTC interrupt */
"movb %b2, %%cs:rtc_flag\n\t"
"\n1:\n\t"
"xchgb %b2, %%cs:rtc_flag\n\t" /* Serialize */
"testb %b2, %b2\n\t"
"jz 1b\n\t"
/* Read "before" TSC */
"rdtsc\n\t"
/* Store "before" TSC on stack */
"pushl %0\n\t"
/* Wait for another RTC interrupt */
"xorb %b2, %b2\n\t"
"movb %b2, %%cs:rtc_flag\n\t"
"\n1:\n\t"
"xchgb %b2, %%cs:rtc_flag\n\t" /* Serialize */
"testb %b2, %b2\n\t"
"jz 1b\n\t"
/* Read "after" TSC */
"rdtsc\n\t"
/* Retrieve "before" TSC on stack */
"popl %1\n\t"
/* Disable interrupts */
"cli\n\t"
)
: "=a" ( after ), "=d" ( before ), "=Q" ( temp )
: "2" ( 0 ) );
*noise = ( after - before );
return 0;
}
/** 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,
};
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