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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2EA6DC54E8D for ; Tue, 12 May 2020 05:59:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 091B12072B for ; Tue, 12 May 2020 05:59:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="VtznbKbe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728150AbgELF71 (ORCPT ); Tue, 12 May 2020 01:59:27 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:41902 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726028AbgELF70 (ORCPT ); Tue, 12 May 2020 01:59:26 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 04C5wFf3136196; Tue, 12 May 2020 05:59:06 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id; s=corp-2020-01-29; bh=el87G9AX5/V/KBiW2l/xDS9bfY+fmEvCw2blEwfatGE=; b=VtznbKbeeteRyzVv0QWSl2sclFXxFTIWQBsPG6asAj90HOrkSij2Pdi/OxcBnV+ABvKs +t2WIa3+tWfftSxWCyicplUZvBJxlUQhDgH7ZBgtYZ9Sc8SRacUNSwjyET62Uxw65XmZ E47Z8SKIca3b0qu7SMzVYaVz1HBegyr1fgZHp8RB8pGCZehCXzUGxDOD4u/2aiop4ssL JQd/E2AjeA2WZXu9dSE3UCxjSbhsI1rCIMpDGrURb5XCtjea+16kySOrRX6zs9JzYksO nOIQmQog6NC4YXlomlbuGcT46LwAvQiVoMHF0zL8AmG6Ru9hQYbNlYv00usTq87kDe7h Rw== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2130.oracle.com with ESMTP id 30x3gmgwhr-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 12 May 2020 05:59:06 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 04C5rsA8051857; Tue, 12 May 2020 05:57:06 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3030.oracle.com with ESMTP id 30ydspr27r-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 12 May 2020 05:57:06 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 04C5v2Og028243; Tue, 12 May 2020 05:57:02 GMT Received: from localhost.uk.oracle.com (/10.175.210.30) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 11 May 2020 22:57:01 -0700 From: Alan Maguire To: ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org Cc: joe@perches.com, linux@rasmusvillemoes.dk, arnaldo.melo@gmail.com, yhs@fb.com, kafai@fb.com, songliubraving@fb.com, andriin@fb.com, john.fastabend@gmail.com, kpsingh@chromium.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Alan Maguire Subject: [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Date: Tue, 12 May 2020 06:56:38 +0100 Message-Id: <1589263005-7887-1-git-send-email-alan.maguire@oracle.com> X-Mailer: git-send-email 1.8.3.1 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9618 signatures=668687 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 suspectscore=0 mlxscore=0 adultscore=0 mlxlogscore=999 malwarescore=0 bulkscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120052 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9618 signatures=668687 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 mlxlogscore=999 clxscore=1015 spamscore=0 lowpriorityscore=0 phishscore=0 bulkscore=0 malwarescore=0 priorityscore=1501 mlxscore=0 suspectscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120052 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The printk family of functions support printing specific pointer types using %p format specifiers (MAC addresses, IP addresses, etc). For full details see Documentation/core-api/printk-formats.rst. This patchset proposes introducing a "print typed pointer" format specifier "%pT"; the argument associated with the specifier is of form "struct btf_ptr *" which consists of a .ptr value and a .type value specifying a stringified type (e.g. "struct sk_buff") or an .id value specifying a BPF Type Format (BTF) id identifying the appropriate type it points to. There is already support in kernel/bpf/btf.c for "show" functionality; the changes here generalize that support from seq-file specific verifier display to the more generic case and add another specific use case; snprintf()-style rendering of type information to a provided buffer. This support is then used to support printk rendering of types, but the intent is to provide a function that might be useful in other in-kernel scenarios; for example: - ftrace could possibly utilize the function to support typed display of function arguments by cross-referencing BTF function information to derive the types of arguments - oops/panic messaging could extend the information displayed to dig into data structures associated with failing functions The above potential use cases hint at a potential reply to a reasonable objection that such typed display should be solved by tracing programs, where the in kernel tracing records data and the userspace program prints it out. While this is certainly the recommended approach for most cases, I believe having an in-kernel mechanism would be valuable also. The function the printk() family of functions rely on could potentially be used directly for other use cases like ftrace where we might have the BTF ids of the pointers we wish to display; its signature is as follows: int btf_type_snprintf_show(const struct btf *btf, u32 type_id, void *obj, char *buf, int len, u64 flags); So if ftrace say had the BTF ids of the types of arguments, we see that the above would allow us to convert the pointer data into displayable form. To give a flavour for what the printed-out data looks like, here we use pr_info() to display a struct sk_buff *. struct sk_buff *skb = alloc_skb(64, GFP_KERNEL); pr_info("%pT", BTF_PTR_TYPE(skb, "struct sk_buff")); ...gives us: (struct sk_buff){ .transport_header = (__u16)65535, .mac_header = (__u16)65535, .end = (sk_buff_data_t)192, .head = (unsigned char *)000000007524fd8b, .data = (unsigned char *)000000007524fd8b, .truesize = (unsigned int)768, .users = (refcount_t){ .refs = (atomic_t){ .counter = (int)1, }, }, } For bpf_trace_printk() a "struct __btf_ptr *" is used as argument; see tools/testing/selftests/bpf/progs/netif_receive_skb.c for example usage. The hope is that this functionality will be useful for debugging, and possibly help facilitate the cases mentioned above in the future. Changes since v1: - changed format to be more drgn-like, rendering indented type info along with type names by default (Alexei) - zeroed values are omitted (Arnaldo) by default unless the '0' modifier is specified (Alexei) - added an option to print pointer values without obfuscation. The reason to do this is the sysctls controlling pointer display are likely to be irrelevant in many if not most tracing contexts. Some questions on this in the outstanding questions section below... - reworked printk format specifer so that we no longer rely on format %pT but instead use a struct * which contains type information (Rasmus). This simplifies the printk parsing, makes use more dynamic and also allows specification by BTF id as well as name. - ensured that BTF-specific printk code is bracketed by #if ENABLED(CONFIG_BTF_PRINTF) - removed incorrect patch which tried to fix dereferencing of resolved BTF info for vmlinux; instead we skip modifiers for the relevant case (array element type/size determination) (Alexei). - fixed issues with negative snprintf format length (Rasmus) - added test cases for various data structure formats; base types, typedefs, structs, etc. - tests now iterate through all typedef, enum, struct and unions defined for vmlinux BTF and render a version of the target dummy value which is either all zeros or all 0xff values; the idea is this exercises the "skip if zero" and "print everything" cases. - added support in BPF for using the %pT format specifier in bpf_trace_printk() - added BPF tests which ensure %pT format specifier use works (Alexei). Outstanding issues - currently %pT is not allowed in BPF programs when lockdown is active prohibiting BPF_READ; is that sufficient? - do we want to further restrict the non-obfuscated pointer format specifier %pTx; for example blocking unprivileged BPF programs from using it? - likely still need a better answer for vmlinux BTF initialization than the current approach taken; early boot initialization is one way to go here. - may be useful to have a "print integers as hex" format modifier (Joe) Important note: if running test_printf.ko - the version in the bpf-next tree will induce a panic when running the fwnode_pointer() tests due to a kobject issue; applying the patch in https://lkml.org/lkml/2020/4/17/389 ...resolved this issue for me. Alan Maguire (7): bpf: provide function to get vmlinux BTF information bpf: move to generic BTF show support, apply it to seq files/strings checkpatch: add new BTF pointer format specifier printk: add type-printing %pT format specifier which uses BTF printk: extend test_printf to test %pT BTF-based format specifier bpf: add support for %pT format specifier for bpf_trace_printk() helper bpf: add tests for %pT format specifier Documentation/core-api/printk-formats.rst | 15 + include/linux/bpf.h | 2 + include/linux/btf.h | 46 +- include/linux/printk.h | 16 + include/uapi/linux/bpf.h | 27 +- kernel/bpf/btf.c | 794 ++++++++++++++++++--- kernel/bpf/verifier.c | 18 +- kernel/trace/bpf_trace.c | 21 +- lib/Kconfig | 16 + lib/test_printf.c | 301 ++++++++ lib/vsprintf.c | 113 +++ scripts/checkpatch.pl | 2 +- tools/include/uapi/linux/bpf.h | 27 +- .../selftests/bpf/prog_tests/trace_printk_btf.c | 83 +++ .../selftests/bpf/progs/netif_receive_skb.c | 81 +++ 15 files changed, 1439 insertions(+), 123 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_printk_btf.c create mode 100644 tools/testing/selftests/bpf/progs/netif_receive_skb.c -- 1.8.3.1