From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 450C9C433EF for ; Thu, 21 Apr 2022 03:03:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:CC:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=/e5t6Adx/pE1xWkZxDW59Pn66hNgp7DxdJJdDs9T0j0=; b=dXeOcoj4L1Jogx c5jSvujksjHZU3/bLobZd91xxxWf7AXpp57HXKvupVsgJl1smzmittwXKbNA3apt7+hmzXZE9Km7H ujTkWl/4Ua7LlPNn1jyMNgTRIiu91PXgsnuOAP90Wv9fKcItcgTxOjHfGrwVPOv9gdY3r9YFPdLDo 62BgW7zBfCW4nEI2PeFGQ7LfFKjWCvsjN7dhDv9ORV/cBlbahphGccJHcEaFabetgCywK8pIE5rYi uzijKmyBHYfO+mWv/tDJxfFDdqhI0XkY/lu/92dHJ8wt6wCk52BOH43PXuvt76aQuOFfIjEQ3csUG s7AXoiRCcjRQwaUoVVcQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nhN5A-00BGvC-TK; Thu, 21 Apr 2022 03:02:12 +0000 Received: from szxga03-in.huawei.com ([45.249.212.189]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nhN56-00BGrY-Gb for linux-arm-kernel@lists.infradead.org; Thu, 21 Apr 2022 03:02:10 +0000 Received: from kwepemi500013.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KkMdx2TDrzCrcc; Thu, 21 Apr 2022 10:57:25 +0800 (CST) Received: from [10.67.111.192] (10.67.111.192) by kwepemi500013.china.huawei.com (7.221.188.120) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 21 Apr 2022 11:01:50 +0800 Message-ID: <0c8976f2-c2d9-8f32-3d2a-725c060fc7e9@huawei.com> Date: Thu, 21 Apr 2022 11:01:49 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH bpf-next v2 2/6] ftrace: Fix deadloop caused by direct call in ftrace selftest Content-Language: en-US To: Steven Rostedt CC: , , , , , Catalin Marinas , Will Deacon , Ingo Molnar , Daniel Borkmann , Alexei Starovoitov , Zi Shen Lim , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , "David S . Miller" , Hideaki YOSHIFUJI , David Ahern , Thomas Gleixner , Borislav Petkov , Dave Hansen , , , Shuah Khan , Mark Rutland , Ard Biesheuvel , Pasha Tatashin , Peter Collingbourne , Daniel Kiss , Sudeep Holla , Steven Price , Marc Zyngier , Mark Brown , Kumar Kartikeya Dwivedi , Delyan Kratunov References: <20220414162220.1985095-1-xukuohai@huawei.com> <20220414162220.1985095-3-xukuohai@huawei.com> <20220420192405.4e43a966@gandalf.local.home> From: Xu Kuohai In-Reply-To: <20220420192405.4e43a966@gandalf.local.home> X-Originating-IP: [10.67.111.192] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemi500013.china.huawei.com (7.221.188.120) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220420_200208_911953_07370B04 X-CRM114-Status: GOOD ( 18.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 4/21/2022 7:24 AM, Steven Rostedt wrote: > On Thu, 14 Apr 2022 12:22:16 -0400 > Xu Kuohai wrote: > >> After direct call is enabled for arm64, ftrace selftest enters a >> dead loop: >> >> : >> 00 bti c >> 01 mov x9, x30 : >> 02 bl ----------> 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 make trace_direct_tramp() a weak symbol and rewrite it for >> arm64. >> >> To detect this issue directly, call DYN_FTRACE_TEST_NAME() before >> register_ftrace_graph(). >> >> Reported-by: Li Huafei >> Signed-off-by: Xu Kuohai >> --- >> arch/arm64/kernel/entry-ftrace.S | 10 ++++++++++ >> kernel/trace/trace_selftest.c | 4 +++- >> 2 files changed, 13 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S >> index dfe62c55e3a2..e58eb06ec9b2 100644 >> --- a/arch/arm64/kernel/entry-ftrace.S >> +++ b/arch/arm64/kernel/entry-ftrace.S >> @@ -357,3 +357,13 @@ SYM_CODE_START(return_to_handler) >> ret >> SYM_CODE_END(return_to_handler) >> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ >> + >> +#ifdef CONFIG_FTRACE_SELFTEST >> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS >> +SYM_FUNC_START(trace_direct_tramp) >> + mov x10, x30 >> + mov x30, x9 >> + ret x10 >> +SYM_FUNC_END(trace_direct_tramp) >> +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */ >> +#endif /* CONFIG_FTRACE_SELFTEST */ >> diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c >> index abcadbe933bb..38b0d5c9a1e0 100644 >> --- a/kernel/trace/trace_selftest.c >> +++ b/kernel/trace/trace_selftest.c >> @@ -785,7 +785,7 @@ static struct fgraph_ops fgraph_ops __initdata = { >> }; >> >> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS >> -noinline __noclone static void trace_direct_tramp(void) { } >> +void __weak trace_direct_tramp(void) { } >> #endif >> >> /* > > >> @@ -868,6 +868,8 @@ trace_selftest_startup_function_graph(struct tracer *trace, >> if (ret) >> goto out; >> >> + DYN_FTRACE_TEST_NAME(); > > This doesn't look like it belongs in this patch. > > -- Steve This was added to run trace_direct_tramp() separately before registering function graph, so the dead loop can be caught accurately. However, the dead loop can also be caught when running function graph test, so this is somewhat unnecessary and will be removed in v3. > >> + >> ret = register_ftrace_graph(&fgraph_ops); >> if (ret) { >> warn_failed_init_tracer(trace, ret); > > . _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel