src/arch/x86/interface/pcbios/rtc_entropy.c - ipxe - Git at Google

 /*
  * 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;

 /** 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
  *
  */
 static void 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 */
 }

 /**
  * 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();
 	enable_irq ( RTC_IRQ );
 	rtc_enable_int();

 	/* 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:
 	rtc_disable_int();
 	disable_irq ( RTC_IRQ );
 	rtc_unhook_isr();
  err_no_tsc:
 	return rc;
 }

 /**
  * Disable entropy gathering
  *
  */
 static void rtc_entropy_disable ( void ) {

 	/* Disable RTC interrupts and unhook ISR */
 	rtc_disable_int();
 	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,
 };
	/*
	* 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;

	/** 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
	*
	*/
	static void 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 */
	}

	/**
	* 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();
	enable_irq ( RTC_IRQ );
	rtc_enable_int();

	/* 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:
	rtc_disable_int();
	disable_irq ( RTC_IRQ );
	rtc_unhook_isr();
	err_no_tsc:
	return rc;
	}

	/**
	* Disable entropy gathering
	*
	*/
	static void rtc_entropy_disable ( void ) {

	/* Disable RTC interrupts and unhook ISR */
	rtc_disable_int();
	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,
	};