From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>,
bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org,
daniel@iogearbox.net, andrii@kernel.org, davem@davemloft.net,
kuba@kernel.org, edumazet@google.com, pabeni@redhat.com,
pablo@netfilter.org, fw@strlen.de,
netfilter-devel@vger.kernel.org, lorenzo.bianconi@redhat.com,
brouer@redhat.com, toke@redhat.com
Subject: Re: [PATCH v3 bpf-next 1/5] bpf: Add support for forcing kfunc args to be referenced
Date: Wed, 18 May 2022 23:36:13 +0530 [thread overview]
Message-ID: <20220518180613.su37c23ckgc5irmu@apollo.legion> (raw)
In-Reply-To: <8912c7c2-9396-f7d8-74e2-a2560fbaad56@fb.com>
On Wed, May 18, 2022 at 11:28:12PM IST, Yonghong Song wrote:
>
>
> On 5/18/22 3:43 AM, Lorenzo Bianconi wrote:
> > From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> >
> > Similar to how we detect mem, size pairs in kfunc, teach verifier to
> > treat __ref suffix on argument name to imply that it must be a
> > referenced pointer when passed to kfunc. This is required to ensure that
> > kfunc that operate on some object only work on acquired pointers and not
> > normal PTR_TO_BTF_ID with same type which can be obtained by pointer
> > walking. Release functions need not specify such suffix on release
> > arguments as they are already expected to receive one referenced
> > argument.
> >
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > ---
> > kernel/bpf/btf.c | 40 ++++++++++++++++++++++++++++++----------
> > net/bpf/test_run.c | 5 +++++
> > 2 files changed, 35 insertions(+), 10 deletions(-)
> >
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 2f0b0440131c..83a354732d96 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -6021,18 +6021,13 @@ static bool __btf_type_is_scalar_struct(struct bpf_verifier_log *log,
> > return true;
> > }
> > -static bool is_kfunc_arg_mem_size(const struct btf *btf,
> > - const struct btf_param *arg,
> > - const struct bpf_reg_state *reg)
> > +static bool btf_param_match_suffix(const struct btf *btf,
> > + const struct btf_param *arg,
> > + const char *suffix)
> > {
> > - int len, sfx_len = sizeof("__sz") - 1;
> > - const struct btf_type *t;
> > + int len, sfx_len = strlen(suffix);
> > const char *param_name;
> > - t = btf_type_skip_modifiers(btf, arg->type, NULL);
> > - if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
> > - return false;
> > -
> > /* In the future, this can be ported to use BTF tagging */
> > param_name = btf_name_by_offset(btf, arg->name_off);
> > if (str_is_empty(param_name))
> > @@ -6041,12 +6036,31 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
> > if (len < sfx_len)
> > return false;
> > param_name += len - sfx_len;
> > - if (strncmp(param_name, "__sz", sfx_len))
> > + if (strncmp(param_name, suffix, sfx_len))
> > return false;
> > return true;
> > }
> > +static bool is_kfunc_arg_ref(const struct btf *btf,
> > + const struct btf_param *arg)
> > +{
> > + return btf_param_match_suffix(btf, arg, "__ref");
>
> Do we also need to do btf_type_skip_modifiers and to ensure
> the type after skipping modifiers are a pointer type?
> The current implementation should work for
> bpf_kfunc_call_test_ref(), but with additional checking
> we may avoid some accidental mistakes.
>
The point where this check happens, arg[i].type is already known to be a pointer
type, after skipping modifiers.
> > +}
> > +
> > +static bool is_kfunc_arg_mem_size(const struct btf *btf,
> > + const struct btf_param *arg,
> > + const struct bpf_reg_state *reg)
> > +{
> > + const struct btf_type *t;
> > +
> > + t = btf_type_skip_modifiers(btf, arg->type, NULL);
> > + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
> > + return false;
> > +
> > + return btf_param_match_suffix(btf, arg, "__sz");
> > +}
> > +
> > static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > const struct btf *btf, u32 func_id,
> > struct bpf_reg_state *regs,
> > @@ -6115,6 +6129,12 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > return -EINVAL;
> > }
> > + /* Check if argument must be a referenced pointer */
> > + if (is_kfunc && is_kfunc_arg_ref(btf, args + i) && !reg->ref_obj_id) {
> > + bpf_log(log, "R%d must be referenced\n", regno);
> > + return -EINVAL;
> > + }
> > +
> > ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
> > ref_tname = btf_name_by_offset(btf, ref_t->name_off);
> > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> > index 4d08cca771c7..adbc7dd18511 100644
> > --- a/net/bpf/test_run.c
> > +++ b/net/bpf/test_run.c
> > @@ -690,6 +690,10 @@ noinline void bpf_kfunc_call_test_mem_len_fail2(u64 *mem, int len)
> > {
> > }
> > +noinline void bpf_kfunc_call_test_ref(struct prog_test_ref_kfunc *p__ref)
> > +{
> > +}
> > +
> > __diag_pop();
> [...]
--
Kartikeya
next prev parent reply other threads:[~2022-05-18 18:05 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-18 10:43 [PATCH v3 bpf-next 0/5] net: netfilter: add kfunc helper to update ct timeout Lorenzo Bianconi
2022-05-18 10:43 ` [PATCH v3 bpf-next 1/5] bpf: Add support for forcing kfunc args to be referenced Lorenzo Bianconi
2022-05-18 17:58 ` Yonghong Song
2022-05-18 18:06 ` Kumar Kartikeya Dwivedi [this message]
2022-05-18 18:23 ` Yonghong Song
2022-05-18 10:43 ` [PATCH v3 bpf-next 2/5] selftests/bpf: Add verifier selftests for forced kfunc ref args Lorenzo Bianconi
2022-05-18 18:25 ` Yonghong Song
2022-05-18 10:43 ` [PATCH v3 bpf-next 3/5] net: netfilter: add kfunc helper to update ct timeout Lorenzo Bianconi
2022-05-18 20:42 ` Toke Høiland-Jørgensen
2022-05-18 10:43 ` [PATCH v3 bpf-next 4/5] net: netfilter: add kfunc helper to add a new ct entry Lorenzo Bianconi
2022-05-18 20:47 ` Toke Høiland-Jørgensen
2022-05-18 21:08 ` Lorenzo Bianconi
2022-05-18 22:14 ` Alexei Starovoitov
2022-05-18 22:43 ` Kumar Kartikeya Dwivedi
2022-05-19 10:45 ` Toke Høiland-Jørgensen
2022-05-19 11:23 ` Kumar Kartikeya Dwivedi
2022-05-19 17:00 ` Yonghong Song
2022-05-19 17:10 ` Kumar Kartikeya Dwivedi
2022-05-19 2:06 ` kernel test robot
2022-05-18 10:43 ` [PATCH v3 bpf-next 5/5] selftests/bpf: add selftest for bpf_xdp_ct_add and bpf_ct_refresh_timeout kfunc Lorenzo Bianconi
2022-05-18 18:55 ` Yonghong Song
2022-05-18 20:38 ` Lorenzo Bianconi
2022-05-20 22:04 ` Andrii Nakryiko
2022-05-21 9:56 ` Lorenzo Bianconi
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