From: Daniel Borkmann <daniel@iogearbox.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>, davem@davemloft.net
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com,
linux-security-module@vger.kernel.org, acme@redhat.com,
jamorris@linux.microsoft.com, jannh@google.com,
kpsingh@google.com
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: implement CAP_BPF
Date: Tue, 12 May 2020 17:05:12 +0200 [thread overview]
Message-ID: <fcc61b50-16f7-4fc9-5cd4-7def57f37c35@iogearbox.net> (raw)
In-Reply-To: <20200508215340.41921-3-alexei.starovoitov@gmail.com>
On 5/8/20 11:53 PM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
>
> Implement permissions as stated in uapi/linux/capability.h
> In order to do that the verifier allow_ptr_leaks flag is split
> into allow_ptr_leaks and bpf_capable flags and they are set as:
> env->allow_ptr_leaks = perfmon_capable();
> env->bpf_capable = bpf_capable();
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 70ad009577f8..a6893746cd87 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1293,7 +1293,7 @@ static void __mark_reg_unknown(const struct bpf_verifier_env *env,
> reg->type = SCALAR_VALUE;
> reg->var_off = tnum_unknown;
> reg->frameno = 0;
> - reg->precise = env->subprog_cnt > 1 || !env->allow_ptr_leaks;
> + reg->precise = env->subprog_cnt > 1 || !env->bpf_capable;
> __mark_reg_unbounded(reg);
> }
>
> @@ -1425,8 +1425,9 @@ static int check_subprogs(struct bpf_verifier_env *env)
> continue;
> if (insn[i].src_reg != BPF_PSEUDO_CALL)
> continue;
> - if (!env->allow_ptr_leaks) {
> - verbose(env, "function calls to other bpf functions are allowed for root only\n");
> + if (!env->bpf_capable) {
> + verbose(env,
> + "function calls to other bpf functions are allowed for CAP_BPF and CAP_SYS_ADMIN\n");
> return -EPERM;
> }
> ret = add_subprog(env, i + insn[i].imm + 1);
> @@ -1960,7 +1961,7 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno,
> bool new_marks = false;
> int i, err;
>
> - if (!env->allow_ptr_leaks)
> + if (!env->bpf_capable)
> /* backtracking is root only for now */
> return 0;
>
> @@ -2208,7 +2209,7 @@ static int check_stack_write(struct bpf_verifier_env *env,
> reg = &cur->regs[value_regno];
>
> if (reg && size == BPF_REG_SIZE && register_is_const(reg) &&
> - !register_is_null(reg) && env->allow_ptr_leaks) {
> + !register_is_null(reg) && env->bpf_capable) {
> if (dst_reg != BPF_REG_FP) {
> /* The backtracking logic can only recognize explicit
> * stack slot address like [fp - 8]. Other spill of
> @@ -3428,7 +3429,7 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
> * Spectre masking for stack ALU.
> * See also retrieve_ptr_limit().
> */
> - if (!env->allow_ptr_leaks) {
> + if (!env->bpf_capable) {
> char tn_buf[48];
>
> tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
> @@ -7229,7 +7230,7 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env,
> insn_stack[env->cfg.cur_stack++] = w;
> return 1;
> } else if ((insn_state[w] & 0xF0) == DISCOVERED) {
> - if (loop_ok && env->allow_ptr_leaks)
> + if (loop_ok && env->bpf_capable)
> return 0;
> verbose_linfo(env, t, "%d: ", t);
> verbose_linfo(env, w, "%d: ", w);
> @@ -8338,7 +8339,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
> if (env->max_states_per_insn < states_cnt)
> env->max_states_per_insn = states_cnt;
>
> - if (!env->allow_ptr_leaks && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
> + if (!env->bpf_capable && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
> return push_jmp_history(env, cur);
>
> if (!add_new_state)
> @@ -9998,7 +9999,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
> insn->code = BPF_JMP | BPF_TAIL_CALL;
>
> aux = &env->insn_aux_data[i + delta];
> - if (env->allow_ptr_leaks && !expect_blinding &&
> + if (env->bpf_capable && !expect_blinding &&
> prog->jit_requested &&
> !bpf_map_key_poisoned(aux) &&
> !bpf_map_ptr_poisoned(aux) &&
> @@ -10725,7 +10726,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
> env->insn_aux_data[i].orig_idx = i;
> env->prog = *prog;
> env->ops = bpf_verifier_ops[env->prog->type];
> - is_priv = capable(CAP_SYS_ADMIN);
> + is_priv = bpf_capable();
>
> if (!btf_vmlinux && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
> mutex_lock(&bpf_verifier_lock);
> @@ -10766,7 +10767,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
> if (attr->prog_flags & BPF_F_ANY_ALIGNMENT)
> env->strict_alignment = false;
>
> - env->allow_ptr_leaks = is_priv;
> + env->allow_ptr_leaks = perfmon_capable();
> + env->bpf_capable = bpf_capable();
Probably more of a detail, but it feels weird to tie perfmon_capable() into the BPF
core and use it in various places there. I would rather make this a proper bpf_*
prefixed helper and add a more descriptive name (what does it have to do with perf
or monitoring directly?). For example, all the main functionality could be under
`bpf_base_capable()` and everything with potential to leak pointers or mem to user
space as `bpf_leak_capable()`. Then inside include/linux/capability.h this can still
resolve under the hood to something like:
static inline bool bpf_base_capable(void)
{
return capable(CAP_BPF) || capable(CAP_SYS_ADMIN);
}
static inline bool bpf_leak_capable(void)
{
return perfmon_capable();
}
Thanks,
Daniel
next prev parent reply other threads:[~2020-05-12 15:05 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 21:53 [PATCH v5 bpf-next 0/3] Introduce CAP_BPF Alexei Starovoitov
2020-05-08 21:53 ` [PATCH v5 bpf-next 1/3] bpf, capability: " Alexei Starovoitov
2020-05-08 21:53 ` [PATCH v5 bpf-next 2/3] bpf: implement CAP_BPF Alexei Starovoitov
2020-05-12 0:12 ` sdf
2020-05-12 2:36 ` Alexei Starovoitov
2020-05-12 12:50 ` Jordan Glover
2020-05-12 15:46 ` Alexei Starovoitov
2020-05-12 15:54 ` sdf
2020-05-12 18:39 ` Alexei Starovoitov
2020-05-12 14:35 ` Daniel Borkmann
2020-05-12 18:25 ` Alexei Starovoitov
2020-05-12 20:07 ` Daniel Borkmann
2020-05-12 22:56 ` Alexei Starovoitov
2020-05-12 15:05 ` Daniel Borkmann [this message]
2020-05-12 18:29 ` Alexei Starovoitov
2020-05-12 20:09 ` Daniel Borkmann
2020-05-12 20:27 ` Daniel Borkmann
2020-05-12 23:01 ` Alexei Starovoitov
2020-05-08 21:53 ` [PATCH v5 bpf-next 3/3] selftests/bpf: use CAP_BPF and CAP_PERFMON in tests Alexei Starovoitov
2020-05-08 22:45 ` [PATCH v5 bpf-next 0/3] Introduce CAP_BPF Casey Schaufler
2020-05-08 23:00 ` Alexei Starovoitov
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