Commit 6ba43b76 authored by KP Singh's avatar KP Singh Committed by Alexei Starovoitov

bpf: Attachment verification for BPF_MODIFY_RETURN

- Allow BPF_MODIFY_RETURN attachment only to functions that are:

    * Whitelisted for error injection by checking
      within_error_injection_list. Similar discussions happened for the
      bpf_override_return helper.

    * security hooks, this is expected to be cleaned up with the LSM
      changes after the KRSI patches introduce the LSM_HOOK macro:

        https://lore.kernel.org/bpf/20200220175250.10795-1-kpsingh@chromium.org/

- The attachment is currently limited to functions that return an int.
  This can be extended later other types (e.g. PTR).
Signed-off-by: default avatarKP Singh <kpsingh@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200304191853.1529-5-kpsingh@chromium.org
parent ae240823
...@@ -3710,14 +3710,26 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, ...@@ -3710,14 +3710,26 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
nr_args--; nr_args--;
} }
if ((prog->expected_attach_type == BPF_TRACE_FEXIT || if (arg == nr_args) {
prog->expected_attach_type == BPF_MODIFY_RETURN) && if (prog->expected_attach_type == BPF_TRACE_FEXIT) {
arg == nr_args) {
if (!t) if (!t)
/* Default prog with 5 args. 6th arg is retval. */
return true; return true;
/* function return type */
t = btf_type_by_id(btf, t->type); t = btf_type_by_id(btf, t->type);
} else if (prog->expected_attach_type == BPF_MODIFY_RETURN) {
/* For now the BPF_MODIFY_RETURN can only be attached to
* functions that return an int.
*/
if (!t)
return false;
t = btf_type_skip_modifiers(btf, t->type, NULL);
if (!btf_type_is_int(t)) {
bpf_log(log,
"ret type %s not allowed for fmod_ret\n",
btf_kind_str[BTF_INFO_KIND(t->info)]);
return false;
}
}
} else if (arg >= nr_args) { } else if (arg >= nr_args) {
bpf_log(log, "func '%s' doesn't have %d-th argument\n", bpf_log(log, "func '%s' doesn't have %d-th argument\n",
tname, arg + 1); tname, arg + 1);
......
...@@ -19,6 +19,7 @@ ...@@ -19,6 +19,7 @@
#include <linux/sort.h> #include <linux/sort.h>
#include <linux/perf_event.h> #include <linux/perf_event.h>
#include <linux/ctype.h> #include <linux/ctype.h>
#include <linux/error-injection.h>
#include "disasm.h" #include "disasm.h"
...@@ -9800,6 +9801,33 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env) ...@@ -9800,6 +9801,33 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
return 0; return 0;
} }
#define SECURITY_PREFIX "security_"
static int check_attach_modify_return(struct bpf_verifier_env *env)
{
struct bpf_prog *prog = env->prog;
unsigned long addr = (unsigned long) prog->aux->trampoline->func.addr;
if (within_error_injection_list(addr))
return 0;
/* This is expected to be cleaned up in the future with the KRSI effort
* introducing the LSM_HOOK macro for cleaning up lsm_hooks.h.
*/
if (!strncmp(SECURITY_PREFIX, prog->aux->attach_func_name,
sizeof(SECURITY_PREFIX) - 1)) {
if (!capable(CAP_MAC_ADMIN))
return -EPERM;
return 0;
}
verbose(env, "fmod_ret attach_btf_id %u (%s) is not modifiable\n",
prog->aux->attach_btf_id, prog->aux->attach_func_name);
return -EINVAL;
}
static int check_attach_btf_id(struct bpf_verifier_env *env) static int check_attach_btf_id(struct bpf_verifier_env *env)
{ {
...@@ -10000,6 +10028,9 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) ...@@ -10000,6 +10028,9 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
} }
tr->func.addr = (void *)addr; tr->func.addr = (void *)addr;
prog->aux->trampoline = tr; prog->aux->trampoline = tr;
if (prog->expected_attach_type == BPF_MODIFY_RETURN)
ret = check_attach_modify_return(env);
out: out:
mutex_unlock(&tr->mutex); mutex_unlock(&tr->mutex);
if (ret) if (ret)
......
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