efi_entropy.c File Reference

EFI entropy source. More...

#include <errno.h>
#include <ipxe/entropy.h>
#include <ipxe/profile.h>
#include <ipxe/efi/efi.h>

Go to the source code of this file.

Macros
#define	EFI_ENTROPY_TRIGGER_TIME   10
	Time (in 100ns units) to delay waiting for timer tick.

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
	FILE_SECBOOT (PERMITTED)
struct entropy_source efitick_entropy	__entropy_source (ENTROPY_FALLBACK)
	EFI entropy source.
static int	efi_entropy_enable (void)
	Enable entropy gathering.
static void	efi_entropy_disable (void)
	Disable entropy gathering.
static int	efi_entropy_tick (void)
	Wait for a timer tick.
static int	efi_get_noise (noise_sample_t *noise)
	Get noise sample from timer ticks.

Variables
static EFI_EVENT	tick
	Event used to wait for timer tick.

Detailed Description

EFI entropy source.

Definition in file efi_entropy.c.

Macro Definition Documentation

EFI_ENTROPY_TRIGGER_TIME

#define EFI_ENTROPY_TRIGGER_TIME   10

Time (in 100ns units) to delay waiting for timer tick.

In theory, UEFI allows us to specify a trigger time of zero to simply wait for the next timer tick. In practice, specifying zero seems to often return immediately, which produces almost no entropy. Specify a delay of 1000ns to try to force an existent delay.

Definition at line 48 of file efi_entropy.c.

Referenced by efi_entropy_tick().

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER_OR_UBDL

)

FILE_SECBOOT()

FILE_SECBOOT

(

PERMITTED

)

__entropy_source()

struct entropy_source efitick_entropy __entropy_source

(

ENTROPY_FALLBACK

)

Initial value:

= {
        .name = "efitick",
        .enable = efi_entropy_enable,
        .disable = efi_entropy_disable,
        .get_noise = efi_get_noise,
}

EFI entropy source.

References __entropy_source, and ENTROPY_FALLBACK.

efi_entropy_enable()

int efi_entropy_enable ( void )

static

Enable entropy gathering.

Return values

rc	Return status code

Definition at line 58 of file efi_entropy.c.

                                       {
        EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
        EFI_STATUS efirc;
        int rc;
 
        /* Drop to external TPL to allow timer tick event to take place */
        bs->RestoreTPL ( efi_external_tpl );
 
        /* Create timer tick event */
        if ( ( efirc = bs->CreateEvent ( EVT_TIMER, TPL_NOTIFY, NULL, NULL,
                                         &tick ) ) != 0 ) {
                rc = -EEFI ( efirc );
                DBGC ( &tick, "ENTROPY could not create event: %s\n",
                       strerror ( rc ) );
                return rc;
        }
 
        /* We use essentially the same mechanism as for the BIOS
         * RTC-based entropy source, and so assume the same
         * min-entropy per sample.
         */
        entropy_init ( &efitick_entropy, MIN_ENTROPY ( 1.3 ) );
 
        return 0;
}

References EFI_BOOT_SERVICES::CreateEvent, DBGC, EEFI, efi_external_tpl, efi_systab, entropy_init(), EVT_TIMER, MIN_ENTROPY, NULL, rc, EFI_BOOT_SERVICES::RestoreTPL, strerror(), tick, and TPL_NOTIFY.

efi_entropy_disable()

void efi_entropy_disable ( void )

static

Disable entropy gathering.

Definition at line 88 of file efi_entropy.c.

                                         {
        EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
 
        /* Close timer tick event */
        bs->CloseEvent ( tick );
 
        /* Return to internal TPL */
        bs->RaiseTPL ( efi_internal_tpl );
}

References EFI_BOOT_SERVICES::CloseEvent, efi_internal_tpl, efi_systab, EFI_BOOT_SERVICES::RaiseTPL, and tick.

efi_entropy_tick()

int efi_entropy_tick ( void )

static

Wait for a timer tick.

Return values

low	CPU profiling low-order bits, or negative error

Definition at line 103 of file efi_entropy.c.

                                     {
        EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
        UINTN index;
        uint16_t low;
        EFI_STATUS efirc;
        int rc;
 
        /* Wait for next timer tick */
        if ( ( efirc = bs->SetTimer ( tick, TimerRelative,
                                      EFI_ENTROPY_TRIGGER_TIME ) ) != 0 ) {
                rc = -EEFI ( efirc );
                DBGC ( &tick, "ENTROPY could not set timer: %s\n",
                       strerror ( rc ) );
                return rc;
        }
        if ( ( efirc = bs->WaitForEvent ( 1, &tick, &index ) ) != 0 ) {
                rc = -EEFI ( efirc );
                DBGC ( &tick, "ENTROPY could not wait for timer tick: %s\n",
                       strerror ( rc ) );
                return rc;
        }
 
        /* Get current CPU profiling timestamp low-order bits */
        low = profile_timestamp();
 
        return low;
}

References DBGC, EEFI, EFI_ENTROPY_TRIGGER_TIME, efi_systab, index, low, profile_timestamp(), rc, EFI_BOOT_SERVICES::SetTimer, strerror(), tick, TimerRelative, and EFI_BOOT_SERVICES::WaitForEvent.

Referenced by efi_get_noise().

efi_get_noise()

int efi_get_noise ( noise_sample_t * noise )

static

Get noise sample from timer ticks.

Return values

noise	Noise sample
rc	Return status code

Definition at line 137 of file efi_entropy.c.

                                                   {
        int before;
        int after;
        int rc;
 
        /* Wait for a timer tick */
        before = efi_entropy_tick();
        if ( before < 0 ) {
                rc = before;
                return rc;
        }
 
        /* Wait for another timer tick */
        after = efi_entropy_tick();
        if ( after < 0 ) {
                rc = after;
                return rc;
        }
 
        /* Use TSC delta as noise sample */
        *noise = ( after - before );
 
        return 0;
}

References after, before, efi_entropy_tick(), and rc.

Variable Documentation

tick

EFI_EVENT tick

static

Event used to wait for timer tick.

Definition at line 51 of file efi_entropy.c.

Referenced by efi_entropy_disable(), efi_entropy_enable(), efi_entropy_tick(), and fiber_autoneg().