From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Alan Maguire <alan.maguire@oracle.com>
Cc: ast@kernel.org, daniel@iogearbox.net, yhs@fb.com, andriin@fb.com,
arnaldo.melo@gmail.com, kafai@fb.com, songliubraving@fb.com,
john.fastabend@gmail.com, kpsingh@chromium.org,
linux@rasmusvillemoes.dk, joe@perches.com, pmladek@suse.com,
rostedt@goodmis.org, sergey.senozhatsky@gmail.com,
andriy.shevchenko@linux.intel.com, corbet@lwn.net,
bpf@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v3 bpf-next 0/8] bpf, printk: add BTF-based type printing
Date: Tue, 30 Jun 2020 20:31:37 +0900 [thread overview]
Message-ID: <20200630113137.GA145027@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <1592914031-31049-1-git-send-email-alan.maguire@oracle.com>
On (20/06/23 13:07), Alan Maguire wrote:
> 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,
> },
> },
> }
Hmm. So this can expose the kernel memory layout (IOW do you print out real
%px pointers and so on)? If so, then I'd suggest not to use printk.
Unprivileged /dev/kmsg or /proc/kmsg reads are really OK thing for printk()
log buffer. And if you are going to print pointer hashes instead,
.transport_header = (__u16)65535,
.mac_header = (__u16)65535,
.end = (sk_buff_data_t)192,
.head = (unsigned char *)34897918740, // pointer_hash
.data = (unsigned char *)23942384983, // pointer hash
.truesize = (unsigned int)768,
.users = (refcount_t){
.refs = (atomic_t){
.counter = (int)1,
},
},
then the value of such printouts becomes a bit unclear to me, sorry.
Probably, something like a seq print into a file somewhere in
/sys/kernel/debug/foo, from which only privileged processes can
read, would be a better approach? My 5 cents.
-ss
prev parent reply other threads:[~2020-06-30 11:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 12:07 [PATCH v3 bpf-next 0/8] bpf, printk: add BTF-based type printing Alan Maguire
2020-06-23 12:07 ` [PATCH v3 bpf-next 1/8] bpf: provide function to get vmlinux BTF information Alan Maguire
2020-06-23 12:07 ` [PATCH v3 bpf-next 2/8] bpf: move to generic BTF show support, apply it to seq files/strings Alan Maguire
2020-06-23 12:07 ` [PATCH v3 bpf-next 3/8] checkpatch: add new BTF pointer format specifier Alan Maguire
2020-06-23 12:07 ` [PATCH v3 bpf-next 4/8] printk: add type-printing %pT format specifier which uses BTF Alan Maguire
2020-06-23 12:40 ` Andy Shevchenko
2020-06-23 13:11 ` Rasmus Villemoes
2020-06-26 10:15 ` Petr Mladek
2020-06-26 11:37 ` Alan Maguire
2020-06-29 9:43 ` Petr Mladek
2020-06-23 12:07 ` [PATCH v3 bpf-next 5/8] printk: initialize vmlinux BTF outside of printk in late_initcall() Alan Maguire
2020-06-23 12:07 ` [PATCH v3 bpf-next 6/8] printk: extend test_printf to test %pT BTF-based format specifier Alan Maguire
2020-06-23 13:02 ` Andy Shevchenko
2020-06-23 12:07 ` [PATCH v3 bpf-next 7/8] bpf: add support for %pT format specifier for bpf_trace_printk() helper Alan Maguire
2020-06-23 13:04 ` Andy Shevchenko
2020-06-23 12:07 ` [PATCH v3 bpf-next 8/8] bpf/selftests: add tests for %pT format specifier Alan Maguire
2020-06-23 18:16 ` Andrii Nakryiko
2020-06-30 11:31 ` Sergey Senozhatsky [this message]
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