From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Ellerman Subject: Re: [PATCH] bpf: fix overflow of bpf_jit_limit when PAGE_SIZE >= 64K Date: Fri, 07 Dec 2018 23:31:13 +1100 Message-ID: <87pnudjz72.fsf@concordia.ellerman.id.au> References: <20181206170646.3736-1-mdroth@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Cc: linuxppc-dev@ozlabs.org, Sandipan Das , Daniel Borkmann , Alexei Starovoitov To: Michael Roth , netdev@vger.kernel.org Return-path: Received: from ozlabs.org ([203.11.71.1]:47315 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725997AbeLGMbQ (ORCPT ); Fri, 7 Dec 2018 07:31:16 -0500 In-Reply-To: <20181206170646.3736-1-mdroth@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: Michael Roth writes: > Commit ede95a63b5 introduced a bpf_jit_limit tuneable to limit BPF > JIT allocations. At compile time it defaults to PAGE_SIZE * 40000, > and is adjusted again at init time if MODULES_VADDR is defined. > > For ppc64 kernels, MODULES_VADDR isn't defined, so we're stuck with But maybe it should be, I don't know why we don't define it. > the compile-time default at boot-time, which is 0x9c400000 when > using 64K page size. This overflows the signed 32-bit bpf_jit_limit > value: > > root@ubuntu:/tmp# cat /proc/sys/net/core/bpf_jit_limit > -1673527296 > > and can cause various unexpected failures throughout the network > stack. In one case `strace dhclient eth0` reported: > > setsockopt(5, SOL_SOCKET, SO_ATTACH_FILTER, {len=11, filter=0x105dd27f8}, 16) = -1 ENOTSUPP (Unknown error 524) > > and similar failures can be seen with tools like tcpdump. This doesn't > always reproduce however, and I'm not sure why. The more consistent > failure I've seen is an Ubuntu 18.04 KVM guest booted on a POWER9 host > would time out on systemd/netplan configuring a virtio-net NIC with no > noticeable errors in the logs. > > Fix this by limiting the compile-time default for bpf_jit_limit to > INT_MAX. INT_MAX is a lot more than (4k * 40000), so I guess I'm not clear on whether we should be using PAGE_SIZE here at all. I guess each BPF program uses at least one page is the thinking? Thanks for tracking this down. For some reason none of my ~10 test boxes have hit this, perhaps I don't have new enough userspace? You don't mention why you needed to add BPF_MIN(), I assume because the kernel version of min() has gotten too complicated to work here? Daniel I assume you'll merge this via your tree? cheers > Fixes: ede95a63b5e8 ("bpf: add bpf_jit_limit knob to restrict unpriv allocations") > Cc: linuxppc-dev@ozlabs.org > Cc: Daniel Borkmann > Cc: Sandipan Das > Cc: Alexei Starovoitov > Signed-off-by: Michael Roth > --- > kernel/bpf/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > index b1a3545d0ec8..55de4746cdfd 100644 > --- a/kernel/bpf/core.c > +++ b/kernel/bpf/core.c > @@ -365,7 +365,8 @@ void bpf_prog_kallsyms_del_all(struct bpf_prog *fp) > } > > #ifdef CONFIG_BPF_JIT > -# define BPF_JIT_LIMIT_DEFAULT (PAGE_SIZE * 40000) > +# define BPF_MIN(x, y) ((x) < (y) ? (x) : (y)) > +# define BPF_JIT_LIMIT_DEFAULT BPF_MIN((PAGE_SIZE * 40000), INT_MAX) > > /* All BPF JIT sysctl knobs here. */ > int bpf_jit_enable __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_ALWAYS_ON); > -- > 2.17.1