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selftests/powerpc: Add a test of spectre_v2 mitigations 

This test uses the PMU to count branch prediction hits/misses for a
known loop, and compare the result to the reported spectre v2
mitigation.

This gives us a way of sanity checking that the reported mitigation is
actually in effect.

Sample output for some cases, eg:

  Power9:
    sysfs reports: 'Vulnerable'
     PM_BR_PRED_CCACHE: result        368 running/enabled 5792777124
    PM_BR_MPRED_CCACHE: result        319 running/enabled 5792775546
     PM_BR_PRED_PCACHE: result 2147483281 running/enabled 5792773128
    PM_BR_MPRED_PCACHE: result  213604201 running/enabled 5792771640
    Miss percent 9 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

    sysfs reports: 'Mitigation: Indirect branch serialisation (kernel only)'
     PM_BR_PRED_CCACHE: result        895 running/enabled 5780320920
    PM_BR_MPRED_CCACHE: result        822 running/enabled 5780312414
     PM_BR_PRED_PCACHE: result 2147482754 running/enabled 5780308836
    PM_BR_MPRED_PCACHE: result  213639731 running/enabled 5780307912
    Miss percent 9 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

    sysfs reports: 'Mitigation: Indirect branch cache disabled'
     PM_BR_PRED_CCACHE: result 2147483649 running/enabled 20540186160
    PM_BR_MPRED_CCACHE: result 2147483649 running/enabled 20540180056
     PM_BR_PRED_PCACHE: result          0 running/enabled 20540176090
    PM_BR_MPRED_PCACHE: result          0 running/enabled 20540174182
    Miss percent 100 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

  Power8:
    sysfs reports: 'Vulnerable'
     PM_BR_PRED_CCACHE: result 2147483649 running/enabled 3505888142
    PM_BR_MPRED_CCACHE: result          9 running/enabled 3505882788
    Miss percent 0 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

    sysfs reports: 'Mitigation: Indirect branch cache disabled'
     PM_BR_PRED_CCACHE: result 2147483649 running/enabled 16931421988
    PM_BR_MPRED_CCACHE: result 2147483649 running/enabled 16931416478
    Miss percent 100 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.
    success: spectre_v2

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190520105520.22274-1-mpe@ellerman.id.au
This commit is contained in:
Michael Ellerman 2019-05-20 20:55:20 +10:00
parent a02cbc7ffe
commit c790c3d2b0
5 changed files with 323 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
tools/testing/selftests/powerpc/include/utils.h
View File

@ -34,6 +34,7 @@ int pick_online_cpu(void);
int read_debugfs_file(char *debugfs_file, int *result);
int write_debugfs_file(char *debugfs_file, int result);
int read_sysfs_file(char *debugfs_file, char *result, size_t result_size);
void set_dscr(unsigned long val);
int perf_event_open_counter(unsigned int type,
unsigned long config, int group_fd);

3
tools/testing/selftests/powerpc/security/Makefile
View File

@ -1,6 +1,6 @@
# SPDX-License-Identifier: GPL-2.0+
TEST_GEN_PROGS := rfi_flush
TEST_GEN_PROGS := rfi_flush spectre_v2
top_srcdir = ../../../../..
CFLAGS += -I../../../../../usr/include
@ -8,3 +8,4 @@ CFLAGS += -I../../../../../usr/include
include ../../lib.mk
$(TEST_GEN_PROGS): ../harness.c ../utils.c
$(OUTPUT)/spectre_v2: ../pmu/event.c branch_loops.S

82
tools/testing/selftests/powerpc/security/branch_loops.S Normal file
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@ -0,0 +1,82 @@
// SPDX-License-Identifier: GPL-2.0+
/*
* Copyright 2019, Michael Ellerman, IBM Corp.
*/
#include <ppc-asm.h>
.data
jump_table:
.long 0x0
.long (.Lstate_1 - .Lstate_0)
.long (.Lstate_2 - .Lstate_0)
.long (.Lstate_3 - .Lstate_0)
.long (.Lstate_4 - .Lstate_0)
.long (.Lstate_5 - .Lstate_0)
.long (.Lstate_6 - .Lstate_0)
.long (.Lstate_7 - .Lstate_0)
.text
#define ITER_SHIFT 31
.macro state number
.balign 32
.Lstate_\number:
.if \number==7
li r3, 0
.else
li r3, \number+1
.endif
b .Lloop
.endm
FUNC_START(pattern_cache_loop)
li r3, 0
li r4, 1
sldi r4, r4, ITER_SHIFT
.Lloop: cmpdi r4, 0
beqlr
addi r4, r4, -1
ld r6, jump_table@got(%r2)
sldi r5, r3, 2
lwax r6, r5, r6
ld r7, .Lstate_0@got(%r2)
add r6, r6, r7
mtctr r6
bctr
state 0
state 1
state 2
state 3
state 4
state 5
state 6
state 7
FUNC_END(pattern_cache_loop)
FUNC_START(indirect_branch_loop)
li r3, 1
sldi r3, r3, ITER_SHIFT
1: cmpdi r3, 0
beqlr
addi r3, r3, -1
ld r4, 2f@got(%r2)
mtctr r4
bctr
.balign 32
2: b 1b
FUNC_END(indirect_branch_loop)

218
tools/testing/selftests/powerpc/security/spectre_v2.c Normal file
View File

@ -0,0 +1,218 @@
// SPDX-License-Identifier: GPL-2.0+
/*
* Copyright 2018-2019 IBM Corporation.
*/
#define __SANE_USERSPACE_TYPES__
#include <sys/types.h>
#include <stdint.h>
#include <malloc.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <sys/prctl.h>
#include "utils.h"
#include "../pmu/event.h"
extern void pattern_cache_loop(void);
extern void indirect_branch_loop(void);
static int do_count_loop(struct event *events, bool is_p9, s64 *miss_percent)
{
u64 pred, mpred;
prctl(PR_TASK_PERF_EVENTS_ENABLE);
if (is_p9)
pattern_cache_loop();
else
indirect_branch_loop();
prctl(PR_TASK_PERF_EVENTS_DISABLE);
event_read(&events[0]);
event_read(&events[1]);
// We could scale all the events by running/enabled but we're lazy
// As long as the PMU is uncontended they should all run
FAIL_IF(events[0].result.running != events[0].result.enabled);
FAIL_IF(events[1].result.running != events[1].result.enabled);
pred = events[0].result.value;
mpred = events[1].result.value;
if (is_p9) {
event_read(&events[2]);
event_read(&events[3]);
FAIL_IF(events[2].result.running != events[2].result.enabled);
FAIL_IF(events[3].result.running != events[3].result.enabled);
pred += events[2].result.value;
mpred += events[3].result.value;
}
*miss_percent = 100 * mpred / pred;
return 0;
}
static void setup_event(struct event *e, u64 config, char *name)
{
event_init_named(e, config, name);
e->attr.disabled = 1;
e->attr.exclude_kernel = 1;
e->attr.exclude_hv = 1;
e->attr.exclude_idle = 1;
}
enum spectre_v2_state {
VULNERABLE = 0,
UNKNOWN = 1, // Works with FAIL_IF()
NOT_AFFECTED,
BRANCH_SERIALISATION,
COUNT_CACHE_DISABLED,
COUNT_CACHE_FLUSH_SW,
COUNT_CACHE_FLUSH_HW,
BTB_FLUSH,
};
static enum spectre_v2_state get_sysfs_state(void)
{
enum spectre_v2_state state = UNKNOWN;
char buf[256];
int len;
memset(buf, 0, sizeof(buf));
FAIL_IF(read_sysfs_file("devices/system/cpu/vulnerabilities/spectre_v2", buf, sizeof(buf)));
// Make sure it's NULL terminated
buf[sizeof(buf) - 1] = '\0';
// Trim the trailing newline
len = strlen(buf);
FAIL_IF(len < 1);
buf[len - 1] = '\0';
printf("sysfs reports: '%s'\n", buf);
// Order matters
if (strstr(buf, "Vulnerable"))
state = VULNERABLE;
else if (strstr(buf, "Not affected"))
state = NOT_AFFECTED;
else if (strstr(buf, "Indirect branch serialisation (kernel only)"))
state = BRANCH_SERIALISATION;
else if (strstr(buf, "Indirect branch cache disabled"))
state = COUNT_CACHE_DISABLED;
else if (strstr(buf, "Software count cache flush (hardware accelerated)"))
state = COUNT_CACHE_FLUSH_HW;
else if (strstr(buf, "Software count cache flush"))
state = COUNT_CACHE_FLUSH_SW;
else if (strstr(buf, "Branch predictor state flush"))
state = BTB_FLUSH;
return state;
}
#define PM_BR_PRED_CCACHE 0x040a4 // P8 + P9
#define PM_BR_MPRED_CCACHE 0x040ac // P8 + P9
#define PM_BR_PRED_PCACHE 0x048a0 // P9 only
#define PM_BR_MPRED_PCACHE 0x048b0 // P9 only
#define SPRN_PVR 287
int spectre_v2_test(void)
{
enum spectre_v2_state state;
struct event events[4];
s64 miss_percent;
bool is_p9;
state = get_sysfs_state();
if (state == UNKNOWN) {
printf("Error: couldn't determine spectre_v2 mitigation state?\n");
return -1;
}
memset(events, 0, sizeof(events));
setup_event(&events[0], PM_BR_PRED_CCACHE, "PM_BR_PRED_CCACHE");
setup_event(&events[1], PM_BR_MPRED_CCACHE, "PM_BR_MPRED_CCACHE");
FAIL_IF(event_open(&events[0]));
FAIL_IF(event_open_with_group(&events[1], events[0].fd) == -1);
is_p9 = ((mfspr(SPRN_PVR) >> 16) & 0xFFFF) == 0x4e;
if (is_p9) {
// Count pattern cache too
setup_event(&events[2], PM_BR_PRED_PCACHE, "PM_BR_PRED_PCACHE");
setup_event(&events[3], PM_BR_MPRED_PCACHE, "PM_BR_MPRED_PCACHE");
FAIL_IF(event_open_with_group(&events[2], events[0].fd) == -1);
FAIL_IF(event_open_with_group(&events[3], events[0].fd) == -1);
}
FAIL_IF(do_count_loop(events, is_p9, &miss_percent));
event_report_justified(&events[0], 18, 10);
event_report_justified(&events[1], 18, 10);
event_close(&events[0]);
event_close(&events[1]);
if (is_p9) {
event_report_justified(&events[2], 18, 10);
event_report_justified(&events[3], 18, 10);
event_close(&events[2]);
event_close(&events[3]);
}
printf("Miss percent %lld %%\n", miss_percent);
switch (state) {
case VULNERABLE:
case NOT_AFFECTED:
case COUNT_CACHE_FLUSH_SW:
case COUNT_CACHE_FLUSH_HW:
// These should all not affect userspace branch prediction
if (miss_percent > 15) {
printf("Branch misses > 15%% unexpected in this configuration!\n");
printf("Possible mis-match between reported & actual mitigation\n");
return 1;
}
break;
case BRANCH_SERIALISATION:
// This seems to affect userspace branch prediction a bit?
if (miss_percent > 25) {
printf("Branch misses > 25%% unexpected in this configuration!\n");
printf("Possible mis-match between reported & actual mitigation\n");
return 1;
}
break;
case COUNT_CACHE_DISABLED:
if (miss_percent < 95) {
printf("Branch misses < 20%% unexpected in this configuration!\n");
printf("Possible mis-match between reported & actual mitigation\n");
return 1;
}
break;
case UNKNOWN:
case BTB_FLUSH:
printf("Not sure!\n");
return 1;
}
printf("OK - Measured branch prediction rates match reported spectre v2 mitigation.\n");
return 0;
}
int main(int argc, char *argv[])
{
return test_harness(spectre_v2_test, "spectre_v2");
}

20
tools/testing/selftests/powerpc/utils.c
View File

@ -127,6 +127,26 @@ bool is_ppc64le(void)
return strcmp(uts.machine, "ppc64le") == 0;
}
int read_sysfs_file(char *fpath, char *result, size_t result_size)
{
char path[PATH_MAX] = "/sys/";
int rc = -1, fd;
strncat(path, fpath, PATH_MAX - strlen(path) - 1);
if ((fd = open(path, O_RDONLY)) < 0)
return rc;
rc = read(fd, result, result_size);
close(fd);
if (rc < 0)
return rc;
return 0;
}
int read_debugfs_file(char *debugfs_file, int *result)
{
int rc = -1, fd;