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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72FCDC43334 for ; Mon, 18 Jul 2022 11:10:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234432AbiGRLKQ (ORCPT ); Mon, 18 Jul 2022 07:10:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234408AbiGRLKM (ORCPT ); Mon, 18 Jul 2022 07:10:12 -0400 Received: from wout1-smtp.messagingengine.com (wout1-smtp.messagingengine.com [64.147.123.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C7541F62C; Mon, 18 Jul 2022 04:10:05 -0700 (PDT) Received: from compute2.internal (compute2.nyi.internal [10.202.2.46]) by mailout.west.internal (Postfix) with ESMTP id 1D271320091B; Mon, 18 Jul 2022 07:10:01 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute2.internal (MEProxy); Mon, 18 Jul 2022 07:10:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:date:date:feedback-id:feedback-id:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:sender:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm3; t=1658142600; x= 1658229000; bh=sHwq/Li6q7x+PDGIFv+evLt4wSOyZViEQf7oifqa30k=; b=x OyHFr2Wi6d6DuA/bwQYlXLNiSBUtND0UAReYSPkz6o3yrV1rnFnW3z4NdrweA+8S YfoZe9VDZfuR6iFwGOyyQA42i+PbeNh5pvR6+ZhJ+TJ9+d9X0jFEbaHQMkYKRbU2 CEOwQHIIQ8zS8/U9Cu3kEFN+NsAXk2d+pzU0fNYWjOLETBW7p7vD/XEO7fVjbP35 RHMtwb64Rz1HkMl3c4oW0kAwZPzfS1ZGE94N9dqqpT6fIEA2ra242NgEBMR1ZwAS 24Tv5LKVCELybZjN9o3W0zhAWqSqMWTExXkrQR5qA3Zh6O0NWY+OEel6KD6+9HUP SGcSOotIMw/xpWrTzJZLQ== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvfedrudekkedgfeehucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepkfffgggfuffvvehfhfgjtgfgsehtjeertddtfeejnecuhfhrohhmpeforghr thihnhgrshcurfhumhhpuhhtihhsuceomheslhgrmhgsuggrrdhltheqnecuggftrfgrth htvghrnhepfeekgeeufeeuiedtteffjeetvdfhleelteekheehueethfevudehhedvveek udevnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepmh eslhgrmhgsuggrrdhlth X-ME-Proxy: Feedback-ID: i215944fb:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Mon, 18 Jul 2022 07:09:57 -0400 (EDT) Message-ID: Date: Mon, 18 Jul 2022 14:09:54 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH RFC bpf-next 4/4] selftests/bpf: Fix kprobe get_func_ip tests for CONFIG_X86_KERNEL_IBT Content-Language: en-US To: Jiri Olsa Cc: Andrii Nakryiko , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Networking , bpf , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Masami Hiramatsu , Yutaro Hayakawa References: <20220705190308.1063813-1-jolsa@kernel.org> <20220705190308.1063813-5-jolsa@kernel.org> From: Martynas Pumputis In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 7/18/22 00:43, Jiri Olsa wrote: > On Fri, Jul 08, 2022 at 12:16:35AM +0200, Jiri Olsa wrote: >> On Tue, Jul 05, 2022 at 10:29:17PM -0700, Andrii Nakryiko wrote: >>> On Tue, Jul 5, 2022 at 12:04 PM Jiri Olsa wrote: >>>> >>>> The kprobe can be placed anywhere and user must be aware >>>> of the underlying instructions. Therefore fixing just >>>> the bpf program to 'fix' the address to match the actual >>>> function address when CONFIG_X86_KERNEL_IBT is enabled. >>>> >>>> Signed-off-by: Jiri Olsa >>>> --- >>>> tools/testing/selftests/bpf/progs/get_func_ip_test.c | 7 +++++-- >>>> 1 file changed, 5 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c >>>> index a587aeca5ae0..220d56b7c1dc 100644 >>>> --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c >>>> +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c >>>> @@ -2,6 +2,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> char _license[] SEC("license") = "GPL"; >>>> >>>> @@ -13,6 +14,8 @@ extern const void bpf_modify_return_test __ksym; >>>> extern const void bpf_fentry_test6 __ksym; >>>> extern const void bpf_fentry_test7 __ksym; >>>> >>>> +extern bool CONFIG_X86_KERNEL_IBT __kconfig __weak; >>>> + >>>> __u64 test1_result = 0; >>>> SEC("fentry/bpf_fentry_test1") >>>> int BPF_PROG(test1, int a) >>>> @@ -37,7 +40,7 @@ __u64 test3_result = 0; >>>> SEC("kprobe/bpf_fentry_test3") >>>> int test3(struct pt_regs *ctx) >>>> { >>>> - __u64 addr = bpf_get_func_ip(ctx); >>>> + __u64 addr = bpf_get_func_ip(ctx) - (CONFIG_X86_KERNEL_IBT ? 4 : 0); >>> >>> so for kprobe bpf_get_func_ip() gets an address with 5 byte >>> compensation for `call __fentry__`, but not for endr? Why can't we >>> compensate for endbr inside the kernel code as well? I'd imagine we >>> either do no compensation (and thus we get &bpf_fentry_test3+5 or >>> &bpf_fentry_test3+9, depending on CONFIG_X86_KERNEL_IBT) or full >>> compensation (and thus always get &bpf_fentry_test3), but this >>> in-between solution seems to be the worst of both worlds?... >> >> hm rigth, I guess we should be able to do that in bpf_get_func_ip, >> I'll check > > sorry for late follow up.. > > so the problem is that you can place kprobe anywhere in the function > (on instruction boundary) but the IBT adjustment of kprobe address is > made only if it's at the function entry and there's endbr instruction To add more fun to the issue, not all non-inlined functions get endbr64. For example "skb_release_head_state()" does, while "skb_free_head()" doesn't. > > and that kprobe address is what we return in helper: > > BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs) > { > struct kprobe *kp = kprobe_running(); > > return kp ? (uintptr_t)kp->addr : 0; > } > > so the adjustment would work only for address at function entry, but > would be wrong for address within the function > > perhaps we could add flag to kprobe to indicate the addr adjustment > was done and use it in helper > > but that's why I thought I'd keep bpf_get_func_ip_kprobe as it and > leave it up to user > > kprobe_multi and trampolines are different, because they can be > only at the function entry, so we can adjust the ip properly > > jirka