Commit 6cae5a71 authored by Andrii Nakryiko's avatar Andrii Nakryiko
Browse files

Merge branch 'bpf: Add detection of kfuncs.' 



Alexei Starovoitov says:

====================

From: Alexei Starovoitov <ast@kernel.org>

Allow BPF programs detect at load time whether particular kfunc exists.

Patch 1: Allow ld_imm64 to point to kfunc in the kernel.
Patch 2: Fix relocation of kfunc in ld_imm64 insn when kfunc is in kernel module.
Patch 3: Introduce bpf_ksym_exists() macro.
Patch 4: selftest.

NOTE: detection of kfuncs from light skeleton is not supported yet.
====================

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
parents 0f10f647 95fdf6e3

kernel/bpf/verifier.c

+11 −6
Original line number Diff line number Diff line
@@ -15952,8 +15952,8 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env, 
		goto err_put;

	}









	if (!btf_type_is_var(t)) {









		verbose(env, "pseudo btf_id %d in ldimm64 isn't KIND_VAR.\n", id);









	if (!btf_type_is_var(t) && !btf_type_is_func(t)) {









		verbose(env, "pseudo btf_id %d in ldimm64 isn't KIND_VAR or KIND_FUNC\n", id);









		err = -EINVAL;









		goto err_put;









	}








@@ -15966,6 +15966,14 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,







		err = -ENOENT;









		goto err_put;









	}









	insn[0].imm = (u32)addr;









	insn[1].imm = addr >> 32;

















	if (btf_type_is_func(t)) {









		aux->btf_var.reg_type = PTR_TO_MEM | MEM_RDONLY;









		aux->btf_var.mem_size = 0;









		goto check_btf;









	}

















	datasec_id = find_btf_percpu_datasec(btf);









	if (datasec_id > 0) {








@@ -15978,9 +15986,6 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,







		}









	}

















	insn[0].imm = (u32)addr;









	insn[1].imm = addr >> 32;

















	type = t->type;









	t = btf_type_skip_modifiers(btf, type, NULL);









	if (percpu) {








@@ -16008,7 +16013,7 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,







		aux->btf_var.btf = btf;









		aux->btf_var.btf_id = type;









	}

















check_btf:









	/* check whether we recorded this BTF (and maybe module) already */









	for (i = 0; i < env->used_btf_cnt; i++) {









		if (env->used_btfs[i].btf == btf) {
































tools/lib/bpf/bpf_helpers.h



+5
−0






























Original line number
Diff line number
Diff line







@@ -177,6 +177,11 @@ enum libbpf_tristate {







#define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted")))









#define __kptr __attribute__((btf_type_tag("kptr")))



















#define bpf_ksym_exists(sym) ({									\









	_Static_assert(!__builtin_constant_p(!!sym), #sym " should be marked as __weak");	\









	!!sym;											\









})



















#ifndef ___bpf_concat









#define ___bpf_concat(a, b) a ## b









#endif
































tools/lib/bpf/libbpf.c



+6
−0






























Original line number
Diff line number
Diff line







@@ -7533,6 +7533,12 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,







	ext->is_set = true;









	ext->ksym.kernel_btf_id = kfunc_id;









	ext->ksym.btf_fd_idx = mod_btf ? mod_btf->fd_array_idx : 0;









	/* Also set kernel_btf_obj_fd to make sure that bpf_object__relocate_data()









	 * populates FD into ld_imm64 insn when it's used to point to kfunc.









	 * {kernel_btf_id, btf_fd_idx} -> fixup bpf_call.









	 * {kernel_btf_id, kernel_btf_obj_fd} -> fixup ld_imm64.









	 */









	ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;









	pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n",









		 ext->name, kfunc_id);










































tools/testing/selftests/bpf/progs/task_kfunc_success.c



+19
−1






























Original line number
Diff line number
Diff line







@@ -17,6 +17,10 @@ int err, pid;







 *         TP_PROTO(struct task_struct *p, u64 clone_flags)









 */



















struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym __weak;









void invalid_kfunc(void) __ksym __weak;









void bpf_testmod_test_mod_kfunc(int i) __ksym __weak;



















static bool is_test_kfunc_task(void)









{









	int cur_pid = bpf_get_current_pid_tgid() >> 32;








@@ -26,7 +30,21 @@ static bool is_test_kfunc_task(void)

















static int test_acquire_release(struct task_struct *task)









{









	struct task_struct *acquired;









	struct task_struct *acquired = NULL;



















	if (!bpf_ksym_exists(bpf_task_acquire)) {









		err = 3;









		return 0;









	}









	if (!bpf_ksym_exists(bpf_testmod_test_mod_kfunc)) {









		err = 4;









		return 0;









	}









	if (bpf_ksym_exists(invalid_kfunc)) {









		/* the verifier's dead code elimination should remove this */









		err = 5;









		asm volatile ("goto -1"); /* for (;;); */









	}



















	acquired = bpf_task_acquire(task);









	bpf_task_release(acquired);