From: Steven Rostedt <rostedt@goodmis.org>
To: Xu Kuohai <xukuohai@huawei.com>
Cc: <bpf@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
<linux-kselftest@vger.kernel.org>,
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Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
Zi Shen Lim <zlim.lnx@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>,
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Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
"David S . Miller" <davem@davemloft.net>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
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Sudeep Holla <sudeep.holla@arm.com>,
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Peter Collingbourne <pcc@google.com>,
Mark Brown <broonie@kernel.org>, Delyan Kratunov <delyank@fb.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>
Subject: Re: [PATCH bpf-next v4 2/6] ftrace: Fix deadloop caused by direct call in ftrace selftest
Date: Wed, 18 May 2022 15:57:59 -0400 [thread overview]
Message-ID: <20220518155759.4054d9a2@gandalf.local.home> (raw)
In-Reply-To: <20220517071838.3366093-3-xukuohai@huawei.com>
On Tue, 17 May 2022 03:18:34 -0400
Xu Kuohai <xukuohai@huawei.com> wrote:
> After direct call is enabled for arm64, ftrace selftest enters a
> dead loop:
>
> <trace_selftest_dynamic_test_func>:
> 00 bti c
> 01 mov x9, x30 <trace_direct_tramp>:
> 02 bl <trace_direct_tramp> ----------> ret
> |
> lr/x30 is 03, return to 03
> |
> 03 mov w0, #0x0 <-----------------------------|
> | |
> | dead loop! |
> | |
> 04 ret ---- lr/x30 is still 03, go back to 03 ----|
>
> The reason is that when the direct caller trace_direct_tramp() returns
> to the patched function trace_selftest_dynamic_test_func(), lr is still
> the address after the instrumented instruction in the patched function,
> so when the patched function exits, it returns to itself!
>
> To fix this issue, we need to restore lr before trace_direct_tramp()
> exits, so rewrite a dedicated trace_direct_tramp() for arm64.
>
> Reported-by: Li Huafei <lihuafei1@huawei.com>
> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
> ---
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
-- Steve
next prev parent reply other threads:[~2022-05-18 19:58 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-17 7:18 [PATCH bpf-next v4 0/6] bpf trampoline for arm64 Xu Kuohai
2022-05-17 7:18 ` [PATCH bpf-next v4 1/6] arm64: ftrace: Add ftrace direct call support Xu Kuohai
2022-05-17 7:18 ` [PATCH bpf-next v4 2/6] ftrace: Fix deadloop caused by direct call in ftrace selftest Xu Kuohai
2022-05-18 19:57 ` Steven Rostedt [this message]
2022-05-17 7:18 ` [PATCH bpf-next v4 3/6] bpf: Move is_valid_bpf_tramp_flags() to the public trampoline code Xu Kuohai
2022-05-17 15:53 ` Alexei Starovoitov
2022-05-18 3:35 ` Xu Kuohai
2022-05-17 7:18 ` [PATCH bpf-next v4 4/6] bpf, arm64: Impelment bpf_arch_text_poke() for arm64 Xu Kuohai
2022-05-17 7:18 ` [PATCH bpf-next v4 5/6] bpf, arm64: bpf trampoline " Xu Kuohai
2022-05-17 7:18 ` [PATCH bpf-next v4 6/6] selftests/bpf: Fix trivial typo in fentry_fexit.c Xu Kuohai
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