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Thu, 14 Jan 2021 21:05:36 +0000 Subject: Re: [PATCH bpf-next 2/3] bpf: Add size arg to build_id_parse function To: Jiri Olsa CC: Jiri Olsa , Arnaldo Carvalho de Melo , Alexei Starovoitov , Song Liu , lkml , , Peter Zijlstra , Ingo Molnar , Mark Rutland , Namhyung Kim , Alexander Shishkin , Michael Petlan , Ian Rogers , Stephane Eranian , Alexei Budankov , Andi Kleen , Adrian Hunter References: <20210114134044.1418404-1-jolsa@kernel.org> <20210114134044.1418404-3-jolsa@kernel.org> <19f16729-96d6-cc8e-5bd5-c3f5940365d4@fb.com> <20210114200120.GF1416940@krava> From: Yonghong Song Message-ID: Date: Thu, 14 Jan 2021 13:05:33 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 In-Reply-To: <20210114200120.GF1416940@krava> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:ab59] X-ClientProxiedBy: MWHPR19CA0068.namprd19.prod.outlook.com (2603:10b6:300:94::30) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21e1::13f6] (2620:10d:c090:400::5:ab59) by MWHPR19CA0068.namprd19.prod.outlook.com (2603:10b6:300:94::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3763.9 via Frontend Transport; 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Did you see an issue here? I guess user space can check >> the length of non-zero bits of the build id to decide what kind of >> type it is, right? > > you can have zero bytes in the build id hash, so you need to get the size > > I never saw MD5 being used in practise just SHA1, but we added the > size to be complete and make sure we'll fit with build id, because > there's only limited space in mmap2 event I am asking to check whether we should extend uapi struct bpf_stack_build_id to include build_id_size as well. I guess we can delay this until a real use case. > > jirka > >> >>> >>> Adding size argument to build_id_parse function, that returns (if defined) >>> size of the parsed build id, so we can recognize the build id type. >>> >>> Cc: Alexei Starovoitov >>> Cc: Song Liu >>> Signed-off-by: Jiri Olsa >>> --- >>> include/linux/buildid.h | 3 ++- >>> kernel/bpf/stackmap.c | 2 +- >>> lib/buildid.c | 29 +++++++++++++++++++++-------- >>> 3 files changed, 24 insertions(+), 10 deletions(-) >>> >>> diff --git a/include/linux/buildid.h b/include/linux/buildid.h >>> index 08028a212589..40232f90db6e 100644 >>> --- a/include/linux/buildid.h >>> +++ b/include/linux/buildid.h >>> @@ -6,6 +6,7 @@ >>> #define BUILD_ID_SIZE_MAX 20 >>> -int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id); >>> +int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, >>> + __u32 *size); >>> #endif >>> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c >>> index 55d254a59f07..cabaf7db8efc 100644 >>> --- a/kernel/bpf/stackmap.c >>> +++ b/kernel/bpf/stackmap.c >>> @@ -189,7 +189,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, >>> for (i = 0; i < trace_nr; i++) { >>> vma = find_vma(current->mm, ips[i]); >>> - if (!vma || build_id_parse(vma, id_offs[i].build_id)) { >>> + if (!vma || build_id_parse(vma, id_offs[i].build_id, NULL)) { >>> /* per entry fall back to ips */ >>> id_offs[i].status = BPF_STACK_BUILD_ID_IP; >>> id_offs[i].ip = ips[i]; >>> diff --git a/lib/buildid.c b/lib/buildid.c >>> index 4a4f520c0e29..6156997c3895 100644 >>> --- a/lib/buildid.c >>> +++ b/lib/buildid.c >>> @@ -12,6 +12,7 @@ >>> */ >>> static inline int parse_build_id(void *page_addr, >>> unsigned char *build_id, >>> + __u32 *size, >>> void *note_start, >>> Elf32_Word note_size) >>> { >>> @@ -38,6 +39,8 @@ static inline int parse_build_id(void *page_addr, >>> nhdr->n_descsz); >>> memset(build_id + nhdr->n_descsz, 0, >>> BUILD_ID_SIZE_MAX - nhdr->n_descsz); >>> + if (size) >>> + *size = nhdr->n_descsz; >>> return 0; >>> } >>> new_offs = note_offs + sizeof(Elf32_Nhdr) + >>> @@ -50,7 +53,8 @@ static inline int parse_build_id(void *page_addr, >>> } >> [...] >> >