Re: BUG: unable to handle kernel paging request in bpf_dispatcher_xdp

Jiri Olsa
2022-12-08T18:07:09Z

On Thu, Dec 08, 2022 at 09:48:52AM -0800, Alexei Starovoitov wrote:
> On Wed, Dec 7, 2022 at 11:57 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Tue, Dec 6, 2022 at 7:18 AM Jiri Olsa <olsajiri@gmail.com> wrote:
> > >
> > > On Tue, Dec 06, 2022 at 02:46:43PM +0800, Hao Sun wrote:
> > > > Hao Sun <sunhao.th@gmail.com> 于2022年12月6日周二 11:28写道：
> > > > >
> > > > > Hi,
> > > > >
> > > > > The following crash can be triggered with the BPF prog provided.
> > > > > It seems the verifier passed some invalid progs. I will try to simplify
> > > > > the C reproducer, for now, the following can reproduce this:
> > > > >
> > > > > HEAD commit: ab0350c743d5 selftests/bpf: Fix conflicts with built-in
> > > > > functions in bpf_iter_ksym
> > > > > git tree: bpf-next
> > > > > console log: https://pastebin.com/raw/87RCSnCs
> > > > > kernel config: https://pastebin.com/raw/rZdWLcgK
> > > > > Syz reproducer: https://pastebin.com/raw/4kbwhdEv
> > > > > C reproducer: https://pastebin.com/raw/GFfDn2Gk
> > > > >
> > > >
> > > > Simplified C reproducer: https://pastebin.com/raw/aZgLcPvW
> > > >
> > > > Only two syscalls are required to reproduce this, seems it's an issue
> > > > in XDP test run. Essentially, the reproducer just loads a very simple
> > > > prog and tests run repeatedly and concurrently:
> > > >
> > > > r0 = bpf$PROG_LOAD(0x5, &(0x7f0000000640)=@base={0x6, 0xb,
> > > > &(0x7f0000000500)}, 0x80)
> > > > bpf$BPF_PROG_TEST_RUN(0xa, &(0x7f0000000140)={r0, 0x0, 0x0, 0x0, 0x0,
> > > > 0x0, 0xffffffff, 0x0, 0x0, 0x0, 0x0, 0x0}, 0x48)
> > > >
> > > > Loaded prog:
> > > > 0: (18) r0 = 0x0
> > > > 2: (18) r6 = 0x0
> > > > 4: (18) r7 = 0x0
> > > > 6: (18) r8 = 0x0
> > > > 8: (18) r9 = 0x0
> > > > 10: (95) exit
> > >
> > > hi,
> > > I can reproduce with your config.. it seems related to the
> > > recent static call change:
> > > c86df29d11df bpf: Convert BPF_DISPATCHER to use static_call() (not ftrace)
> > >
> > > I can't reproduce when I revert that commit.. Peter, any idea?
> >
> > Jiri,
> >
> > I see your tested-by tag on Peter's commit c86df29d11df.
> > I assume you're actually tested it, but
> > this syzbot oops shows that even empty bpf prog crashes,
> > so there is something wrong with that commit.
> >
> > What is the difference between this new kconfig and old one that
> > you've tested?
> >
> > I'm trying to understand the severity of the issues and
> > whether we need to revert that commit asap since the merge window
> > is about to start.
>
> Jiri, Peter,
>
> ping.
>
> cc-ing Thorsten, since he's tracking it now.
>
> The config has CONFIG_X86_KERNEL_IBT=y.
> Is it related?

sorry for late reply.. I still did not find the reason,
but I did not try with IBT yet, will test now

jirka