From: Jiri Olsa <jolsa@redhat.com>
To: Yonghong Song <yhs@fb.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andriin@fb.com>,
"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>, Daniel Xu <dxu@dxuuu.xyz>,
Viktor Malik <vmalik@redhat.com>
Subject: Re: [PATCH 09/19] bpf, x64: Allow to use caller address from stack
Date: Mon, 7 Jun 2021 20:13:07 +0200 [thread overview]
Message-ID: <YL5hs/xi3RpbLlKy@krava> (raw)
In-Reply-To: <e590aa58-bdfa-86c1-eaca-79b4e5bff1f3@fb.com>
On Sun, Jun 06, 2021 at 08:07:44PM -0700, Yonghong Song wrote:
>
>
> On 6/5/21 4:10 AM, Jiri Olsa wrote:
> > Currently we call the original function by using the absolute address
> > given at the JIT generation. That's not usable when having trampoline
> > attached to multiple functions. In this case we need to take the
> > return address from the stack.
>
> Here, it is mentioned to take the return address from the stack.
>
> >
> > Adding support to retrieve the original function address from the stack
>
> Here, it is said to take original funciton address from the stack.
sorry if the description is confusing as always, the idea
is to take the function's return address from fentry call:
function
call fentry
xxxx <---- this address
and use it to call the original function body before fexit handler
jirka
>
> > by adding new BPF_TRAMP_F_ORIG_STACK flag for arch_prepare_bpf_trampoline
> > function.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > arch/x86/net/bpf_jit_comp.c | 13 +++++++++----
> > include/linux/bpf.h | 5 +++++
> > 2 files changed, 14 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 2a2e290fa5d8..b77e6bd78354 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -2013,10 +2013,15 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> > if (flags & BPF_TRAMP_F_CALL_ORIG) {
> > restore_regs(m, &prog, nr_args, stack_size);
> > - /* call original function */
> > - if (emit_call(&prog, orig_call, prog)) {
> > - ret = -EINVAL;
> > - goto cleanup;
> > + if (flags & BPF_TRAMP_F_ORIG_STACK) {
> > + emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
>
> This is load double from base_pointer + 8 which should be func return
> address for x86, yet we try to call it.
> I guess I must have missed something
> here. Could you give some explanation?
>
> > + EMIT2(0xff, 0xd0); /* call *rax */
> > + } else {
> > + /* call original function */
> > + if (emit_call(&prog, orig_call, prog)) {
> > + ret = -EINVAL;
> > + goto cleanup;
> > + }
> > }
> > /* remember return value in a stack for bpf prog to access */
> > emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 86dec5001ae2..16fc600503fb 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -554,6 +554,11 @@ struct btf_func_model {
> > */
> > #define BPF_TRAMP_F_SKIP_FRAME BIT(2)
> > +/* Get original function from stack instead of from provided direct address.
> > + * Makes sense for fexit programs only.
> > + */
> > +#define BPF_TRAMP_F_ORIG_STACK BIT(3)
> > +
> > /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
> > * bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2
> > */
> >
>
next prev parent reply other threads:[~2021-06-07 18:13 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-05 11:10 [RFCv3 00/19] x86/ftrace/bpf: Add batch support for direct/tracing attach Jiri Olsa
2021-06-05 11:10 ` [PATCH 01/19] x86/ftrace: Remove extra orig rax move Jiri Olsa
2021-06-05 11:10 ` [PATCH 02/19] x86/ftrace: Remove fault protection code in prepare_ftrace_return Jiri Olsa
2021-06-05 11:10 ` [PATCH 03/19] x86/ftrace: Make function graph use ftrace directly Jiri Olsa
2021-06-08 18:35 ` Andrii Nakryiko
2021-06-08 18:51 ` Jiri Olsa
2021-06-08 19:11 ` Steven Rostedt
2021-06-05 11:10 ` [PATCH 04/19] tracing: Add trampoline/graph selftest Jiri Olsa
2021-06-05 11:10 ` [PATCH 05/19] ftrace: Add ftrace_add_rec_direct function Jiri Olsa
2021-06-05 11:10 ` [PATCH 06/19] ftrace: Add multi direct register/unregister interface Jiri Olsa
2021-06-05 11:10 ` [PATCH 07/19] ftrace: Add multi direct modify interface Jiri Olsa
2021-06-05 11:10 ` [PATCH 08/19] ftrace/samples: Add multi direct interface test module Jiri Olsa
2021-06-05 11:10 ` [PATCH 09/19] bpf, x64: Allow to use caller address from stack Jiri Olsa
2021-06-07 3:07 ` Yonghong Song
2021-06-07 18:13 ` Jiri Olsa [this message]
2021-06-05 11:10 ` [PATCH 10/19] bpf: Allow to store caller's ip as argument Jiri Olsa
2021-06-07 3:21 ` Yonghong Song
2021-06-07 18:15 ` Jiri Olsa
2021-06-08 18:49 ` Andrii Nakryiko
2021-06-08 20:58 ` Jiri Olsa
2021-06-08 21:02 ` Andrii Nakryiko
2021-06-08 21:11 ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 11/19] bpf: Add support to load multi func tracing program Jiri Olsa
2021-06-07 3:56 ` Yonghong Song
2021-06-07 18:18 ` Jiri Olsa
2021-06-07 19:35 ` Yonghong Song
2021-06-05 11:10 ` [PATCH 12/19] bpf: Add bpf_trampoline_alloc function Jiri Olsa
2021-06-05 11:10 ` [PATCH 13/19] bpf: Add support to link multi func tracing program Jiri Olsa
2021-06-07 5:36 ` Yonghong Song
2021-06-07 18:25 ` Jiri Olsa
2021-06-07 19:39 ` Yonghong Song
2021-06-08 15:42 ` Alexei Starovoitov
2021-06-08 18:17 ` Jiri Olsa
2021-06-08 18:49 ` Alexei Starovoitov
2021-06-08 21:07 ` Jiri Olsa
2021-06-08 23:05 ` Alexei Starovoitov
2021-06-09 5:08 ` Andrii Nakryiko
2021-06-09 13:42 ` Jiri Olsa
2021-06-09 13:33 ` Jiri Olsa
2021-06-09 5:18 ` Andrii Nakryiko
2021-06-09 13:53 ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 14/19] libbpf: Add btf__find_by_pattern_kind function Jiri Olsa
2021-06-09 5:29 ` Andrii Nakryiko
2021-06-09 13:59 ` Jiri Olsa
2021-06-09 14:19 ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 15/19] libbpf: Add support to link multi func tracing program Jiri Olsa
2021-06-07 5:49 ` Yonghong Song
2021-06-07 18:28 ` Jiri Olsa
2021-06-07 19:42 ` Yonghong Song
2021-06-07 20:11 ` Jiri Olsa
2021-06-09 5:34 ` Andrii Nakryiko
2021-06-09 14:17 ` Jiri Olsa
2021-06-10 17:05 ` Andrii Nakryiko
2021-06-10 20:35 ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 16/19] selftests/bpf: Add fentry multi func test Jiri Olsa
2021-06-07 6:06 ` Yonghong Song
2021-06-07 18:42 ` Jiri Olsa
2021-06-09 5:40 ` Andrii Nakryiko
2021-06-09 14:29 ` Jiri Olsa
2021-06-10 17:00 ` Andrii Nakryiko
2021-06-10 20:28 ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 17/19] selftests/bpf: Add fexit " Jiri Olsa
2021-06-05 11:10 ` [PATCH 18/19] selftests/bpf: Add fentry/fexit " Jiri Olsa
2021-06-09 5:41 ` Andrii Nakryiko
2021-06-09 14:29 ` Jiri Olsa
2021-06-05 11:10 ` [PATCH 19/19] selftests/bpf: Temporary fix for fentry_fexit_multi_test Jiri Olsa
2021-06-17 20:29 ` [RFCv3 00/19] x86/ftrace/bpf: Add batch support for direct/tracing attach Andrii Nakryiko
2021-06-19 8:33 ` Jiri Olsa
2021-06-19 16:19 ` Yonghong Song
2021-06-19 17:09 ` Jiri Olsa
2021-06-20 16:56 ` Yonghong Song
2021-06-20 17:47 ` Alexei Starovoitov
2021-06-21 6:46 ` Andrii Nakryiko
2021-06-21 6:50 ` Andrii Nakryiko
2021-07-06 20:26 ` Andrii Nakryiko
2021-07-07 15:19 ` Jiri Olsa
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