From: Daniel Borkmann <daniel@iogearbox•net>
To: David Miller <davem@davemloft•net>, ast@fb•com
Cc: borkmann@iogearbox•net, netdev@vger•kernel.org
Subject: Re: more on FP operations
Date: Thu, 20 Apr 2017 23:52:44 +0200 [thread overview]
Message-ID: <58F92DAC.3010706@iogearbox.net> (raw)
In-Reply-To: <20170420.140617.91794616324352770.davem@davemloft.net>
On 04/20/2017 08:06 PM, David Miller wrote:
>
> I'm running test_verifier for testing, and I notice in my JIT that a
> 32-bit move from the frame pointer (BPF_REG_10) ends up in the JIT.
>
> It is from this test:
>
> "unpriv: partial copy of pointer",
> .insns = {
> BPF_MOV32_REG(BPF_REG_1, BPF_REG_10),
> BPF_MOV64_IMM(BPF_REG_0, 0),
> BPF_EXIT_INSN(),
> },
> .errstr_unpriv = "R10 partial copy",
> .result_unpriv = REJECT,
> .result = ACCEPT,
>
> It seems to suggest that privileged code is allowed to do this, but I
> can't think of a legitimate usage.
One thing I could think of right now would be for use in 32 bit
archs, but that would still need to be taught to the verifier
first. Other patterns f.e. like ...
{
"unpriv: adding of fp",
.insns = {
BPF_MOV64_IMM(BPF_REG_1, 0),
BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_10),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.errstr_unpriv = "pointer arithmetic prohibited",
.result_unpriv = REJECT,
.result = ACCEPT,
},
... are currently also possible, but in the above and the partial
copy r1 is always considered as UNKNOWN_VALUE from that point onward
and there's not really much we could do with it anymore, except
perhaps passing to bpf_probe_read() for inspection in tracing for
some reason. Since there are also various other pointers, it is
really only the FP that needs to be special cased for sparc JIT,
right?
> I really want to be able to JIT anything the verifier accepts, but I
> have a hard time justifying adding 32-bit FP register move support,
> adjusting for the stack bias, etc.
>
> Thanks.
next prev parent reply other threads:[~2017-04-20 21:52 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-20 18:06 more on FP operations David Miller
2017-04-20 21:52 ` Daniel Borkmann [this message]
2017-04-20 23:13 ` Alexei Starovoitov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=58F92DAC.3010706@iogearbox.net \
--to=daniel@iogearbox$(echo .)net \
--cc=ast@fb$(echo .)com \
--cc=borkmann@iogearbox$(echo .)net \
--cc=davem@davemloft$(echo .)net \
--cc=netdev@vger$(echo .)kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox