Re: [Potential Spoof] [PATCH bpf-next 3/3] selftests/bpf: reset process and thread affinity after each test/sub-test

[Martin KaFai Lau <kafai@fb.com>]

On Fri, Mar 13, 2020 at 06:39:32PM -0700, Andrii Nakryiko wrote:
> Some tests and sub-tests are setting "custom" thread/process affinity and
> don't reset it back. Instead of requiring each test to undo all this, ensure
> that thread affinity is restored by test_progs test runner itself.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---
>  tools/testing/selftests/bpf/test_progs.c | 42 +++++++++++++++++++++++-
>  tools/testing/selftests/bpf/test_progs.h |  1 +
>  2 files changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index c8cb407482c6..b521e0a512b6 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -1,12 +1,15 @@
>  // SPDX-License-Identifier: GPL-2.0-only
>  /* Copyright (c) 2017 Facebook
>   */
> +#define _GNU_SOURCE
>  #include "test_progs.h"
>  #include "cgroup_helpers.h"
>  #include "bpf_rlimit.h"
>  #include <argp.h>
> -#include <string.h>
> +#include <pthread.h>
> +#include <sched.h>
>  #include <signal.h>
> +#include <string.h>
>  #include <execinfo.h> /* backtrace */
>  
>  /* defined in test_progs.h */
> @@ -90,6 +93,34 @@ static void skip_account(void)
>  	}
>  }
>  
> +static void stdio_restore(void);
> +
> +/* A bunch of tests set custom affinity per-thread and/or per-process. Reset
> + * it after each test/sub-test.
> + */
> +static void reset_affinity() {
> +
> +	cpu_set_t cpuset;
> +	int i, err;
> +
> +	CPU_ZERO(&cpuset);
> +	for (i = 0; i < env.nr_cpus; i++)
> +		CPU_SET(i, &cpuset);
In case the user may run "taskset somemask test_progs",
is it better to store the inital_cpuset at the beginning
of main and then restore to inital_cpuset after each run?

> +
> +	err = sched_setaffinity(0, sizeof(cpuset), &cpuset);
> +	if (err < 0) {
> +		stdio_restore();
> +		fprintf(stderr, "Failed to reset process affinity: %d!\n", err);
> +		exit(-1);
> +	}
> +	err = pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);
> +	if (err < 0) {
> +		stdio_restore();
> +		fprintf(stderr, "Failed to reset thread affinity: %d!\n", err);
> +		exit(-1);
> +	}
> +}