From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yonghong Song Subject: [PATCH bpf] tools/bpftool: fix a percpu_array map dump problem Date: Fri, 27 Jul 2018 16:11:38 -0700 Message-ID: <20180727231138.3318561-1-yhs@fb.com> Mime-Version: 1.0 Content-Type: text/plain Cc: To: , , Return-path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:32872 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730636AbeG1Afx (ORCPT ); Fri, 27 Jul 2018 20:35:53 -0400 Received: from pps.filterd (m0001303.ppops.net [127.0.0.1]) by m0001303.ppops.net (8.16.0.22/8.16.0.22) with SMTP id w6RN7PE0019333 for ; Fri, 27 Jul 2018 16:11:47 -0700 Received: from mail.thefacebook.com ([199.201.64.23]) by m0001303.ppops.net with ESMTP id 2kgb4j08ee-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Fri, 27 Jul 2018 16:11:47 -0700 Sender: netdev-owner@vger.kernel.org List-ID: I hit the following problem when I tried to use bpftool to dump a percpu array. $ sudo ./bpftool map show 61: percpu_array name stub flags 0x0 key 4B value 4B max_entries 1 memlock 4096B ... $ sudo ./bpftool map dump id 61 bpftool: malloc.c:2406: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || \ ((unsigned long) (old_size) >= MINSIZE && \ prev_inuse (old_top) && \ ((unsigned long) old_end & (pagesize - 1)) == 0)' failed. Aborted Further debugging revealed that this is due to miscommunication between bpftool and kernel. For example, for the above percpu_array with value size of 4B. The map info returned to user space has value size of 4B. In bpftool, the values array for lookup is allocated like: info->value_size * get_possible_cpus() = 4 * get_possible_cpus() In kernel (kernel/bpf/syscall.c), the values array size is rounded up to multiple of 8. round_up(map->value_size, 8) * num_possible_cpus() = 8 * num_possible_cpus() So when kernel copies the values to user buffer, the kernel will overwrite beyond user buffer boundary. This patch fixed the issue by allocating and stepping through percpu map value array properly in bpftool. Fixes: 71bb428fe2c19 ("tools: bpf: add bpftool") Signed-off-by: Yonghong Song --- tools/bpf/bpftool/map.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c index 0ee3ba479d87..92bc55f98c4c 100644 --- a/tools/bpf/bpftool/map.c +++ b/tools/bpf/bpftool/map.c @@ -35,6 +35,7 @@ #include #include #include +#include #include #include #include @@ -91,7 +92,8 @@ static bool map_is_map_of_progs(__u32 type) static void *alloc_value(struct bpf_map_info *info) { if (map_is_per_cpu(info->type)) - return malloc(info->value_size * get_possible_cpus()); + return malloc(round_up(info->value_size, 8) * + get_possible_cpus()); else return malloc(info->value_size); } @@ -273,9 +275,10 @@ static void print_entry_json(struct bpf_map_info *info, unsigned char *key, do_dump_btf(&d, info, key, value); } } else { - unsigned int i, n; + unsigned int i, n, step; n = get_possible_cpus(); + step = round_up(info->value_size, 8); jsonw_name(json_wtr, "key"); print_hex_data_json(key, info->key_size); @@ -288,7 +291,7 @@ static void print_entry_json(struct bpf_map_info *info, unsigned char *key, jsonw_int_field(json_wtr, "cpu", i); jsonw_name(json_wtr, "value"); - print_hex_data_json(value + i * info->value_size, + print_hex_data_json(value + i * step, info->value_size); jsonw_end_object(json_wtr); -- 2.14.3