[PATCH] selftests/seccomp: Expand benchmark to per-filter measurements

From: Kees Cook
Date: Mon Jun 01 2020 - 15:49:04 EST


It's useful to see how much (at a minimum) each filter adds to the
syscall overhead. Add additional calculations.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
As part of the performance discussions, this is what I'm adding to the
seccomp selftest in for-next/seccomp to get more details.
https://lore.kernel.org/linux-security-module/202006011116.3F7109A@keescook/T/#md8a6fd608cfd1f3c70aaf9ccc4f09fcc33b5fc1b
This does not include the BPF-bypass mode, which I don't see a way to
do without creating major problems with seccomp. ;)
---
.../selftests/seccomp/seccomp_benchmark.c | 36 +++++++++++++++----
tools/testing/selftests/seccomp/seccomp_bpf.c | 2 --
2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_benchmark.c b/tools/testing/selftests/seccomp/seccomp_benchmark.c
index 5838c8697ec3..eca13fe1fba9 100644
--- a/tools/testing/selftests/seccomp/seccomp_benchmark.c
+++ b/tools/testing/selftests/seccomp/seccomp_benchmark.c
@@ -68,32 +68,54 @@ int main(int argc, char *argv[])
};
long ret;
unsigned long long samples;
- unsigned long long native, filtered;
+ unsigned long long native, filter1, filter2;

if (argc > 1)
samples = strtoull(argv[1], NULL, 0);
else
samples = calibrate();

+ printf("Current BPF sysctl settings:\n");
+ system("sysctl net.core.bpf_jit_enable");
+ system("sysctl net.core.bpf_jit_harden");
printf("Benchmarking %llu samples...\n", samples);

+ /* Native call */
native = timing(CLOCK_PROCESS_CPUTIME_ID, samples) / samples;
printf("getpid native: %llu ns\n", native);

ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
assert(ret == 0);

+ /* One filter */
ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
assert(ret == 0);

- filtered = timing(CLOCK_PROCESS_CPUTIME_ID, samples) / samples;
- printf("getpid RET_ALLOW: %llu ns\n", filtered);
+ filter1 = timing(CLOCK_PROCESS_CPUTIME_ID, samples) / samples;
+ printf("getpid RET_ALLOW 1 filter: %llu ns\n", filter1);

- printf("Estimated seccomp overhead per syscall: %llu ns\n",
- filtered - native);
+ if (filter1 == native)
+ printf("No overhead measured!? Try running again with more samples.\n");

- if (filtered == native)
- printf("Trying running again with more samples.\n");
+ /* Two filters */
+ ret = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
+ assert(ret == 0);
+
+ filter2 = timing(CLOCK_PROCESS_CPUTIME_ID, samples) / samples;
+ printf("getpid RET_ALLOW 2 filters: %llu ns\n", filter2);
+
+ /* Calculations */
+ printf("Estimated total seccomp overhead for 1 filter: %llu ns\n",
+ filter1 - native);
+
+ printf("Estimated total seccomp overhead for 2 filters: %llu ns\n",
+ filter2 - native);
+
+ printf("Estimated seccomp per-filter overhead: %llu ns\n",
+ filter2 - filter1);
+
+ printf("Estimated seccomp entry overhead: %llu ns\n",
+ filter1 - native - (filter2 - filter1));

return 0;
}
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 4dae278cf77e..402ccb3a4e52 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -3824,7 +3824,6 @@ TEST(user_notification_filter_empty_threaded)

/*
* TODO:
- * - add microbenchmarks
* - expand NNP testing
* - better arch-specific TRACE and TRAP handlers.
* - endianness checking when appropriate
@@ -3832,7 +3831,6 @@ TEST(user_notification_filter_empty_threaded)
* - arch value testing (x86 modes especially)
* - verify that FILTER_FLAG_LOG filters generate log messages
* - verify that RET_LOG generates log messages
- * - ...
*/

TEST_HARNESS_MAIN
--
2.25.1


--
Kees Cook