From: Ingo Molnar <mingo@kernel•org>
To: Eric Dumazet <edumazet@google•com>
Cc: Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Heiko Carstens <heiko.carstens@de•ibm.com>,
Paul Mackerras <paulus@samba•org>,
"H. Peter Anvin" <hpa@zytor•com>,
sparclinux@vger•kernel.org,
Nicolas Dichtel <nicolas.dichtel@6wind•com>,
Alexei Starovoitov <ast@plumgrid•com>,
linux-s390@vger•kernel.org, Russell King <linux@arm•linux.org.uk>,
x86@kernel•org, James Morris <jmorris@namei•org>,
Ingo Molnar <mingo@redhat•com>,
Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>,
"Paul E. McKenney" <paulmck@linux•vnet.ibm.com>,
Xi Wang <xi.wang@gmail•com>, Matt Evans <matt@ozlabs•org>,
Thomas Gleixner <tglx@linutronix•de>,
linux-arm-kernel@lists•infradead.org,
Stelian Nirlu <steliannirlu@gmail•com>,
Nicolas Schichan <nschichan@freebox•fr>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>,
netdev <netdev@vger•kernel.org>,
linux-kernel@vger•kernel.org,
"David S. Miller" <davem@davemloft•net>,
Mi
Subject: Re: [PATCH v3 net-next] fix unsafe set_memory_rw from softirq
Date: Fri, 4 Oct 2013 19:35:40 +0200 [thread overview]
Message-ID: <20131004173540.GB15689@gmail.com> (raw)
In-Reply-To: <CANn89iKkbR0_HaofvC_OVvqRv_Hqj3rATx-Z_4xXeusOasa56g@mail.gmail.com>
* Eric Dumazet <edumazet@google•com> wrote:
> 1)
> >
> > I took a brief look at arch/x86/net/bpf_jit_comp.c while reviewing this
> > patch.
> >
> > You need to split up bpf_jit_compile(), it's an obscenely large, ~600
> > lines long function. We don't do that in modern, maintainable kernel code.
> >
> > 2)
> >
> > This 128 bytes extra padding:
> >
> > /* Most of BPF filters are really small,
> > * but if some of them fill a page, allow at least
> > * 128 extra bytes to insert a random section of int3
> > */
> > sz = round_up(proglen + sizeof(*header) + 128, PAGE_SIZE);
> >
> > why is it done? It's not clear to me from the comment.
> >
>
> commit 314beb9bcabfd6b4542ccbced2402af2c6f6142a
> Author: Eric Dumazet <edumazet@google•com>
> Date: Fri May 17 16:37:03 2013 +0000
>
> x86: bpf_jit_comp: secure bpf jit against spraying attacks
>
> hpa bringed into my attention some security related issues
> with BPF JIT on x86.
>
> This patch makes sure the bpf generated code is marked read only,
> as other kernel text sections.
>
> It also splits the unused space (we vmalloc() and only use a fraction of
> the page) in two parts, so that the generated bpf code not starts at a
> known offset in the page, but a pseudo random one.
Thanks for the explanation - that makes sense.
Ingo
next prev parent reply other threads:[~2013-10-04 17:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-04 2:24 [PATCH v3 net-next] fix unsafe set_memory_rw from softirq Alexei Starovoitov
2013-10-04 6:47 ` Heiko Carstens
2013-10-04 7:51 ` Ingo Molnar
2013-10-04 13:56 ` Eric Dumazet
2013-10-04 17:35 ` Ingo Molnar [this message]
2013-10-04 17:49 ` Alexei Starovoitov
2013-10-04 18:00 ` Ingo Molnar
-- strict thread matches above, loose matches on Subject: below --
2013-10-04 4:11 Alexei Starovoitov
2013-10-04 5:16 ` Eric Dumazet
2013-10-04 6:30 ` Alexei Starovoitov
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