Commit 6ca21620 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

Merge branch 'bpf-reject-attaching-fexit-fmod_ret-to-noreturn-functions' 

Yafang Shao says:

====================
Attaching fexit probes to functions marked with __noreturn may lead to
unpredictable behavior. To avoid this, we will reject attaching probes to
such functions. Currently, there is no ideal solution, so we will hardcode
a check for all __noreturn functions.

Once a more robust solution is implemented, this workaround can be removed.

v4->v5:
- Remove unnecessary functions (Alexei)
- Use BTF_ID directly (Alexei)

v3->v4: https://lore.kernel.org/bpf/20250317121735.86515-1-laoar.shao@gmail.com/
- Reject also fmod_ret (Alexei)
- Fix build warnings and remove unnecessary functions (Alexei)

v1->v2: https://lore.kernel.org/bpf/20250223062735.3341-1-laoar.shao@gmail.com/
- keep tools/objtool/noreturns.h as is (Josh)
- Add noreturns.h to objtool/sync-check.sh (Josh)
- Add verbose for the reject and simplify the test case (Song)

v1: https://lore.kernel.org/bpf/20250211023359.1570-1-laoar.shao@gmail.com/
====================

Link: https://patch.msgid.link/20250318114447.75484-1-laoar.shao@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parents f4edc66e be16ddea

kernel/bpf/verifier.c

+32 −0
Original line number Diff line number Diff line
@@ -23215,6 +23215,33 @@ BTF_ID(func, __rcu_read_unlock) 
#endif

BTF_SET_END(btf_id_deny)









/* fexit and fmod_ret can't be used to attach to __noreturn functions.









 * Currently, we must manually list all __noreturn functions here. Once a more









 * robust solution is implemented, this workaround can be removed.









 */









BTF_SET_START(noreturn_deny)









#ifdef CONFIG_IA32_EMULATION









BTF_ID(func, __ia32_sys_exit)









BTF_ID(func, __ia32_sys_exit_group)









#endif









#ifdef CONFIG_KUNIT









BTF_ID(func, __kunit_abort)









BTF_ID(func, kunit_try_catch_throw)









#endif









#ifdef CONFIG_MODULES









BTF_ID(func, __module_put_and_kthread_exit)









#endif









#ifdef CONFIG_X86_64









BTF_ID(func, __x64_sys_exit)









BTF_ID(func, __x64_sys_exit_group)









#endif









BTF_ID(func, do_exit)









BTF_ID(func, do_group_exit)









BTF_ID(func, kthread_complete_and_exit)









BTF_ID(func, kthread_exit)









BTF_ID(func, make_task_dead)









BTF_SET_END(noreturn_deny)

















static bool can_be_sleepable(struct bpf_prog *prog)









{









	if (prog->type == BPF_PROG_TYPE_TRACING) {








@@ -23301,6 +23328,11 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)







	} else if (prog->type == BPF_PROG_TYPE_TRACING &&









		   btf_id_set_contains(&btf_id_deny, btf_id)) {









		return -EINVAL;









	} else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||









		   prog->expected_attach_type == BPF_MODIFY_RETURN) &&









		   btf_id_set_contains(&noreturn_deny, btf_id)) {









		verbose(env, "Attaching fexit/fmod_ret to __noreturn functions is rejected.\n");









		return -EINVAL;









	}

















	key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id);

























tools/testing/selftests/bpf/prog_tests/fexit_noreturns.c
0 → 100644



+9
−0






























Original line number
Diff line number
Diff line









// SPDX-License-Identifier: GPL-2.0



















#include <test_progs.h>









#include "fexit_noreturns.skel.h"



















void test_fexit_noreturns(void)









{









	RUN_TESTS(fexit_noreturns);









}
























tools/testing/selftests/bpf/progs/fexit_noreturns.c
0 → 100644



+15
−0






























Original line number
Diff line number
Diff line









// SPDX-License-Identifier: GPL-2.0



















#include <linux/bpf.h>









#include <bpf/bpf_helpers.h>









#include <bpf/bpf_tracing.h>









#include "bpf_misc.h"



















char _license[] SEC("license") = "GPL";



















SEC("fexit/do_exit")









__failure __msg("Attaching fexit/fmod_ret to __noreturn functions is rejected.")









int BPF_PROG(noreturns)









{









	return 0;









}