Commit aa3d65de authored by Viktor Malik's avatar Viktor Malik Committed by Alexei Starovoitov
Browse files

bpf/selftests: Test fentry attachment to shadowed functions 



Adds a new test that tries to attach a program to fentry of two
functions of the same name, one located in vmlinux and the other in
bpf_testmod.

To avoid conflicts with existing tests, a new function
"bpf_fentry_shadow_test" was created both in vmlinux and in bpf_testmod.

The previous commit fixed a bug which caused this test to fail. The
verifier would always use the vmlinux function's address as the target
trampoline address, hence trying to create two trampolines for a single
address, which is forbidden.

The test (similarly to other fentry/fexit tests) is not working on arm64
at the moment.

Signed-off-by: default avatarViktor Malik <vmalik@redhat.com>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/5fe2f364190b6f79b085066ed7c5989c5bc475fa.1678432753.git.vmalik@redhat.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 31bf1dbc

net/bpf/test_run.c

+5 −0
Original line number Diff line number Diff line
@@ -560,6 +560,11 @@ long noinline bpf_kfunc_call_test4(signed char a, short b, int c, long d) 
	return (long)a + (long)b + (long)c + d;

}



int noinline bpf_fentry_shadow_test(int a)

{

	return a + 1;

}



struct prog_test_member1 {

	int a;

};

tools/testing/selftests/bpf/DENYLIST.aarch64

+1 −0
Original line number Diff line number Diff line
@@ -44,6 +44,7 @@ lookup_key # test_lookup_key__attach unexp 
lru_bug                                          # lru_bug__attach unexpected error: -524 (errno 524)

modify_return                                    # modify_return__attach failed unexpected error: -524 (errno 524)

module_attach                                    # skel_attach skeleton attach failed: -524

module_fentry_shadow                             # bpf_link_create unexpected bpf_link_create: actual -524 < expected 0

mptcp/base                                       # run_test mptcp unexpected error: -524 (errno 524)

netcnt                                           # packets unexpected packets: actual 10001 != expected 10000

rcu_read_lock                                    # failed to attach: ERROR: strerror_r(-524)=22

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

+6 −0
Original line number Diff line number Diff line
@@ -268,6 +268,12 @@ static const struct btf_kfunc_id_set bpf_testmod_kfunc_set = { 
	.set   = &bpf_testmod_check_kfunc_ids,

};



noinline int bpf_fentry_shadow_test(int a)

{

	return a + 2;

}

EXPORT_SYMBOL_GPL(bpf_fentry_shadow_test);



extern int bpf_fentry_test1(int a);



static int bpf_testmod_init(void)

tools/testing/selftests/bpf/prog_tests/module_fentry_shadow.c

0 → 100644
+128 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2022 Red Hat */

#include <test_progs.h>

#include <bpf/btf.h>

#include "bpf/libbpf_internal.h"

#include "cgroup_helpers.h"



static const char *module_name = "bpf_testmod";

static const char *symbol_name = "bpf_fentry_shadow_test";



static int get_bpf_testmod_btf_fd(void)

{

	struct bpf_btf_info info;

	char name[64];

	__u32 id = 0, len;

	int err, fd;



	while (true) {

		err = bpf_btf_get_next_id(id, &id);

		if (err) {

			log_err("failed to iterate BTF objects");

			return err;

		}



		fd = bpf_btf_get_fd_by_id(id);

		if (fd < 0) {

			if (errno == ENOENT)

				continue; /* expected race: BTF was unloaded */

			err = -errno;

			log_err("failed to get FD for BTF object #%d", id);

			return err;

		}



		len = sizeof(info);

		memset(&info, 0, sizeof(info));

		info.name = ptr_to_u64(name);

		info.name_len = sizeof(name);



		err = bpf_obj_get_info_by_fd(fd, &info, &len);

		if (err) {

			err = -errno;

			log_err("failed to get info for BTF object #%d", id);

			close(fd);

			return err;

		}



		if (strcmp(name, module_name) == 0)

			return fd;



		close(fd);

	}

	return -ENOENT;

}



void test_module_fentry_shadow(void)

{

	struct btf *vmlinux_btf = NULL, *mod_btf = NULL;

	int err, i;

	int btf_fd[2] = {};

	int prog_fd[2] = {};

	int link_fd[2] = {};

	__s32 btf_id[2] = {};



	LIBBPF_OPTS(bpf_prog_load_opts, load_opts,

		.expected_attach_type = BPF_TRACE_FENTRY,

	);



	const struct bpf_insn trace_program[] = {

		BPF_MOV64_IMM(BPF_REG_0, 0),

		BPF_EXIT_INSN(),

	};



	vmlinux_btf = btf__load_vmlinux_btf();

	if (!ASSERT_OK_PTR(vmlinux_btf, "load_vmlinux_btf"))

		return;



	btf_fd[1] = get_bpf_testmod_btf_fd();

	if (!ASSERT_GE(btf_fd[1], 0, "get_bpf_testmod_btf_fd"))

		goto out;



	mod_btf = btf_get_from_fd(btf_fd[1], vmlinux_btf);

	if (!ASSERT_OK_PTR(mod_btf, "btf_get_from_fd"))

		goto out;



	btf_id[0] = btf__find_by_name_kind(vmlinux_btf, symbol_name, BTF_KIND_FUNC);

	if (!ASSERT_GT(btf_id[0], 0, "btf_find_by_name"))

		goto out;



	btf_id[1] = btf__find_by_name_kind(mod_btf, symbol_name, BTF_KIND_FUNC);

	if (!ASSERT_GT(btf_id[1], 0, "btf_find_by_name"))

		goto out;



	for (i = 0; i < 2; i++) {

		load_opts.attach_btf_id = btf_id[i];

		load_opts.attach_btf_obj_fd = btf_fd[i];

		prog_fd[i] = bpf_prog_load(BPF_PROG_TYPE_TRACING, NULL, "GPL",

					   trace_program,

					   sizeof(trace_program) / sizeof(struct bpf_insn),

					   &load_opts);

		if (!ASSERT_GE(prog_fd[i], 0, "bpf_prog_load"))

			goto out;



		/* If the verifier incorrectly resolves addresses of the

		 * shadowed functions and uses the same address for both the

		 * vmlinux and the bpf_testmod functions, this will fail on

		 * attempting to create two trampolines for the same address,

		 * which is forbidden.

		 */

		link_fd[i] = bpf_link_create(prog_fd[i], 0, BPF_TRACE_FENTRY, NULL);

		if (!ASSERT_GE(link_fd[i], 0, "bpf_link_create"))

			goto out;

	}



	err = bpf_prog_test_run_opts(prog_fd[0], NULL);

	ASSERT_OK(err, "running test");



out:

	btf__free(vmlinux_btf);

	btf__free(mod_btf);

	for (i = 0; i < 2; i++) {

		if (btf_fd[i])

			close(btf_fd[i]);

		if (prog_fd[i] > 0)

			close(prog_fd[i]);

		if (link_fd[i] > 0)

			close(link_fd[i]);

	}

}