On Wed, Jan 03, 2024 at 01:53:59PM -0500, Barret Rhoden wrote:
SNIP
> +
> +
> +/* Test that attempting to load a bad program fails. */
> +#define test_bad(PROG) ({ \
> + struct array_elem_test *skel; \
> + int err; \
> + skel = array_elem_test__open(); \
> + if (!ASSERT_OK_PTR(skel, "array_elem_test open")) \
> + return; \
> + bpf_program__set_autoload(skel->progs.x_bad_ ## PROG, true); \
> + err = array_elem_test__load(skel); \
> + ASSERT_ERR(err, "array_elem_test load " # PROG); \
> + array_elem_test__destroy(skel); \
> +})
I wonder we could use the existing RUN_TESTS macro and use tags
in programs like we do for example in progs/test_global_func1.c:
SEC("tc")
__failure __msg("combined stack size of 4 calls is 544")
int global_func1(struct __sk_buff *skb)
jirka
> +
> +void test_test_array_elem(void)
> +{
> + if (test__start_subtest("array_elem_access_all"))
> + test_access_all();
> + if (test__start_subtest("array_elem_oob_access"))
> + test_oob_access();
> + if (test__start_subtest("array_elem_access_array_map_infer_sz"))
> + test_access_array_map_infer_sz();
> + if (test__start_subtest("array_elem_bad_map_array_access"))
> + test_bad(map_array_access);
> + if (test__start_subtest("array_elem_bad_bss_array_access"))
> + test_bad(bss_array_access);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/array_elem_test.c b/tools/testing/selftests/bpf/progs/array_elem_test.c
> new file mode 100644
> index 000000000000..9d48afc933f0
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/array_elem_test.c
> @@ -0,0 +1,195 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Google LLC. */
> +#include <stdbool.h>
> +#include <linux/types.h>
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include "bpf_misc.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +int target_pid = 0;
> +
> +#define NR_MAP_ELEMS 100
> +
> +/*
> + * We want to test valid accesses into an array, but we also need to fool the
> + * verifier. If we just do for (i = 0; i < 100; i++), the verifier knows the
> + * value of i and can tell we're inside the array.
> + *
> + * This "lookup" array is just the values 0, 1, 2..., such that
> + * lookup_indexes[i] == i. (set by userspace). But the verifier doesn't know
> + * that.
> + */
> +unsigned int lookup_indexes[NR_MAP_ELEMS];
> +
> +/* Arrays can be in the BSS or inside a map element. Make sure both work. */
> +int bss_elems[NR_MAP_ELEMS];
> +
> +struct map_array {
> + int elems[NR_MAP_ELEMS];
> +};
> +
> +/*
> + * This is an ARRAY_MAP of a single struct, and that struct is an array of
> + * elements. Userspace can mmap the map as if it was just a basic array of
> + * elements. Though if you make an ARRAY_MAP where the *values* are ints, don't
> + * forget that bpf map elements are rounded up to 8 bytes.
> + *
> + * Once you get the pointer to the base of the inner array, you can access all
> + * of the elements without another bpf_map_lookup_elem(), which is useful if you
> + * are operating on multiple elements while holding a spinlock.
> + */
> +struct {
> + __uint(type, BPF_MAP_TYPE_ARRAY);
> + __uint(max_entries, 1);
> + __type(key, int);
> + __type(value, struct map_array);
> + __uint(map_flags, BPF_F_MMAPABLE);
> +} arraymap SEC(".maps");
> +
> +static struct map_array *get_map_array(void)
> +{
> + int zero = 0;
> +
> + return bpf_map_lookup_elem(&arraymap, &zero);
> +}
> +
> +static int *get_map_elems(void)
> +{
> + struct map_array *arr = get_map_array();
> +
> + if (!arr)
> + return NULL;
> + return arr->elems;
> +}
> +
> +/*
> + * Test that we can access all elements, and that we are accessing the element
> + * we think we are accessing.
> + */
> +static void access_all(void)
> +{
> + int *map_elems = get_map_elems();
> + int *x;
> +
> + for (int i = 0; i < NR_MAP_ELEMS; i++) {
> + x = bpf_array_elem(map_elems, NR_MAP_ELEMS, lookup_indexes[i]);
> + if (x)
> + *x = i;
> + }
> +
> + for (int i = 0; i < NR_MAP_ELEMS; i++) {
> + x = bpf_array_sz_elem(bss_elems, lookup_indexes[i]);
> + if (x)
> + *x = i;
> + }
> +}
> +
> +SEC("?tp/syscalls/sys_enter_nanosleep")
> +int x_access_all(void *ctx)
> +{
> + if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
> + return 0;
> + access_all();
> + return 0;
> +}
> +
> +/*
> + * Helper for various OOB tests. An out-of-bound access should be handled like
> + * a lookup failure. Specifically, the verifier should ensure we do not access
> + * outside the array. Userspace will check that we didn't access somewhere
> + * inside the array.
> + */
> +static void set_elem_to_1(long idx)
> +{
> + int *map_elems = get_map_elems();
> + int *x;
> +
> + x = bpf_array_elem(map_elems, NR_MAP_ELEMS, idx);
> + if (x)
> + *x = 1;
> + x = bpf_array_sz_elem(bss_elems, idx);
> + if (x)
> + *x = 1;
> +}
> +
> +/*
> + * Test various out-of-bounds accesses.
> + */
> +static void oob_access(void)
> +{
> + set_elem_to_1(NR_MAP_ELEMS + 5);
> + set_elem_to_1(NR_MAP_ELEMS);
> + set_elem_to_1(-1);
> + set_elem_to_1(~0UL);
> +}
> +
> +SEC("?tp/syscalls/sys_enter_nanosleep")
> +int x_oob_access(void *ctx)
> +{
> + if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
> + return 0;
> + oob_access();
> + return 0;
> +}
> +
> +/*
> + * Test that we can use the ARRAY_SIZE-style helper with an array in a map.
> + *
> + * Note that you cannot infer the size of the array from just a pointer; you
> + * have to use the actual elems[100]. i.e. this will fail and should fail to
> + * compile (-Wsizeof-pointer-div):
> + *
> + * int *map_elems = get_map_elems();
> + * x = bpf_array_sz_elem(map_elems, lookup_indexes[i]);
> + */
> +static void access_array_map_infer_sz(void)
> +{
> + struct map_array *arr = get_map_array();
> + int *x;
> +
> + for (int i = 0; i < NR_MAP_ELEMS; i++) {
> + x = bpf_array_sz_elem(arr->elems, lookup_indexes[i]);
> + if (x)
> + *x = i;
> + }
> +}
> +
> +SEC("?tp/syscalls/sys_enter_nanosleep")
> +int x_access_array_map_infer_sz(void *ctx)
> +{
> + if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
> + return 0;
> + access_array_map_infer_sz();
> + return 0;
> +}
> +
> +
> +
> +SEC("?tp/syscalls/sys_enter_nanosleep")
> +int x_bad_map_array_access(void *ctx)
> +{
> + int *map_elems = get_map_elems();
> +
> + /*
> + * Need to check to promote map_elems from MAP_OR_NULL to MAP so that we
> + * fail to load below for the right reason.
> + */
> + if (!map_elems)
> + return 0;
> + /* Fail to load: we don't prove our access is inside map_elems[] */
> + for (int i = 0; i < NR_MAP_ELEMS; i++)
> + map_elems[lookup_indexes[i]] = i;
> + return 0;
> +}
> +
> +SEC("?tp/syscalls/sys_enter_nanosleep")
> +int x_bad_bss_array_access(void *ctx)
> +{
> + /* Fail to load: we don't prove our access is inside bss_elems[] */
> + for (int i = 0; i < NR_MAP_ELEMS; i++)
> + bss_elems[lookup_indexes[i]] = i;
> + return 0;
> +}
> diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
> index 2fd59970c43a..002bab44cde2 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_misc.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
> @@ -135,4 +135,47 @@
> /* make it look to compiler like value is read and written */
> #define __sink(expr) asm volatile("" : "+g"(expr))
>
> +/*
> + * Access an array element within a bound, such that the verifier knows the
> + * access is safe.
> + *
> + * This macro asm is the equivalent of:
> + *
> + * if (!arr)
> + * return NULL;
> + * if (idx >= arr_sz)
> + * return NULL;
> + * return &arr[idx];
> + *
> + * The index (___idx below) needs to be a u64, at least for certain versions of
> + * the BPF ISA, since there aren't u32 conditional jumps.
> + */
> +#define bpf_array_elem(arr, arr_sz, idx) ({ \
> + typeof(&(arr)[0]) ___arr = arr; \
> + __u64 ___idx = idx; \
> + if (___arr) { \
> + asm volatile("if %[__idx] >= %[__bound] goto 1f; \
> + %[__idx] *= %[__size]; \
> + %[__arr] += %[__idx]; \
> + goto 2f; \
> + 1:; \
> + %[__arr] = 0; \
> + 2: \
> + " \
> + : [__arr]"+r"(___arr), [__idx]"+r"(___idx) \
> + : [__bound]"r"((arr_sz)), \
> + [__size]"i"(sizeof(typeof((arr)[0]))) \
> + : "cc"); \
> + } \
> + ___arr; \
> +})
> +
> +/*
> + * Convenience wrapper for bpf_array_elem(), where we compute the size of the
> + * array. Be sure to use an actual array, and not a pointer, just like with the
> + * ARRAY_SIZE macro.
> + */
> +#define bpf_array_sz_elem(arr, idx) \
> + bpf_array_elem(arr, sizeof(arr) / sizeof((arr)[0]), idx)
> +
> #endif
> --
> 2.43.0.472.g3155946c3a-goog
>
>
