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Message-ID: <CAADnVQJ_ZCzMmT1aBsNXEBFfYNSVBdBXmLocjR0PPEWtYQrQFw@mail.gmail.com>
Date: Mon, 11 Mar 2024 19:09:25 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: 梦龙董 <dongmenglong.8@...edance.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>,
Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>, "David S. Miller" <davem@...emloft.net>,
David Ahern <dsahern@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>,
X86 ML <x86@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Quentin Monnet <quentin@...valent.com>,
bpf <bpf@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>,
linux-riscv <linux-riscv@...ts.infradead.org>, linux-s390 <linux-s390@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>, linux-trace-kernel@...r.kernel.org,
"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support
to record and check the accessed args
On Mon, Mar 11, 2024 at 7:01 PM 梦龙董 <dongmenglong.8@...edance.com> wrote:
>
> On Tue, Mar 12, 2024 at 9:46 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Mon, Mar 11, 2024 at 2:34 AM Menglong Dong
> > <dongmenglong.8@...edance.com> wrote:
> > >
> > > In this commit, we add the 'accessed_args' field to struct bpf_prog_aux,
> > > which is used to record the accessed index of the function args in
> > > btf_ctx_access().
> > >
> > > Meanwhile, we add the function btf_check_func_part_match() to compare the
> > > accessed function args of two function prototype. This function will be
> > > used in the following commit.
> > >
> > > Signed-off-by: Menglong Dong <dongmenglong.8@...edance.com>
> > > ---
> > > include/linux/bpf.h | 4 ++
> > > kernel/bpf/btf.c | 108 +++++++++++++++++++++++++++++++++++++++++++-
> > > 2 files changed, 110 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 95e07673cdc1..0f677fdcfcc7 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -1461,6 +1461,7 @@ struct bpf_prog_aux {
> > > const struct btf_type *attach_func_proto;
> > > /* function name for valid attach_btf_id */
> > > const char *attach_func_name;
> > > + u64 accessed_args;
> > > struct bpf_prog **func;
> > > void *jit_data; /* JIT specific data. arch dependent */
> > > struct bpf_jit_poke_descriptor *poke_tab;
> > > @@ -2565,6 +2566,9 @@ struct bpf_reg_state;
> > > int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog);
> > > int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
> > > struct btf *btf, const struct btf_type *t);
> > > +int btf_check_func_part_match(struct btf *btf1, const struct btf_type *t1,
> > > + struct btf *btf2, const struct btf_type *t2,
> > > + u64 func_args);
> > > const char *btf_find_decl_tag_value(const struct btf *btf, const struct btf_type *pt,
> > > int comp_idx, const char *tag_key);
> > > int btf_find_next_decl_tag(const struct btf *btf, const struct btf_type *pt,
> > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > index 170d017e8e4a..c2a0299d4358 100644
> > > --- a/kernel/bpf/btf.c
> > > +++ b/kernel/bpf/btf.c
> > > @@ -6125,19 +6125,24 @@ static bool is_int_ptr(struct btf *btf, const struct btf_type *t)
> > > }
> > >
> > > static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,
> > > - int off)
> > > + int off, int *aligned_idx)
> > > {
> > > const struct btf_param *args;
> > > const struct btf_type *t;
> > > u32 offset = 0, nr_args;
> > > int i;
> > >
> > > + if (aligned_idx)
> > > + *aligned_idx = -ENOENT;
> > > +
> > > if (!func_proto)
> > > return off / 8;
> > >
> > > nr_args = btf_type_vlen(func_proto);
> > > args = (const struct btf_param *)(func_proto + 1);
> > > for (i = 0; i < nr_args; i++) {
> > > + if (aligned_idx && offset == off)
> > > + *aligned_idx = i;
> > > t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> > > offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
> > > if (off < offset)
> > > @@ -6207,7 +6212,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> > > tname, off);
> > > return false;
> > > }
> > > - arg = get_ctx_arg_idx(btf, t, off);
> > > + arg = get_ctx_arg_idx(btf, t, off, NULL);
> > > args = (const struct btf_param *)(t + 1);
> > > /* if (t == NULL) Fall back to default BPF prog with
> > > * MAX_BPF_FUNC_REG_ARGS u64 arguments.
> > > @@ -6217,6 +6222,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> > > /* skip first 'void *__data' argument in btf_trace_##name typedef */
> > > args++;
> > > nr_args--;
> > > + prog->aux->accessed_args |= (1 << (arg + 1));
> > > + } else {
> > > + prog->aux->accessed_args |= (1 << arg);
> >
> > What do you need this aligned_idx for ?
> > I'd expect that above "accessed_args |= (1 << arg);" is enough.
> >
>
> Which aligned_idx? No aligned_idx in the btf_ctx_access(), and
> aligned_idx is only used in the btf_check_func_part_match().
>
> In the btf_check_func_part_match(), I need to compare the
> t1->args[i] and t2->args[j], which have the same offset. And
> the aligned_idx is to find the "j" according to the offset of
> t1->args[i].
And that's my question.
Why you don't do the max of accessed_args across all attach
points and do btf_check_func_type_match() to that argno
instead of nargs1.
This 'offset += btf_type_is_ptr(t1) ? 8 : roundup...
is odd.
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