Re: [PATCHv4 bpf 1/2] bpf: Fix prog_array_map_poke_run map poke update

[Lee Jones <lee@kernel.org>]

On Thu, 21 Dec 2023, Greg KH wrote:

> On Thu, Dec 21, 2023 at 09:07:45AM +0000, Lee Jones wrote:
> > Dear Stable,
> > 
> > > Lee pointed out issue found by syscaller [0] hitting BUG in prog array
> > > map poke update in prog_array_map_poke_run function due to error value
> > > returned from bpf_arch_text_poke function.
> > > 
> > > There's race window where bpf_arch_text_poke can fail due to missing
> > > bpf program kallsym symbols, which is accounted for with check for
> > > -EINVAL in that BUG_ON call.
> > > 
> > > The problem is that in such case we won't update the tail call jump
> > > and cause imbalance for the next tail call update check which will
> > > fail with -EBUSY in bpf_arch_text_poke.
> > > 
> > > I'm hitting following race during the program load:
> > > 
> > >   CPU 0                             CPU 1
> > > 
> > >   bpf_prog_load
> > >     bpf_check
> > >       do_misc_fixups
> > >         prog_array_map_poke_track
> > > 
> > >                                     map_update_elem
> > >                                       bpf_fd_array_map_update_elem
> > >                                         prog_array_map_poke_run
> > > 
> > >                                           bpf_arch_text_poke returns -EINVAL
> > > 
> > >     bpf_prog_kallsyms_add
> > > 
> > > After bpf_arch_text_poke (CPU 1) fails to update the tail call jump, the next
> > > poke update fails on expected jump instruction check in bpf_arch_text_poke
> > > with -EBUSY and triggers the BUG_ON in prog_array_map_poke_run.
> > > 
> > > Similar race exists on the program unload.
> > > 
> > > Fixing this by moving the update to bpf_arch_poke_desc_update function which
> > > makes sure we call __bpf_arch_text_poke that skips the bpf address check.
> > > 
> > > Each architecture has slightly different approach wrt looking up bpf address
> > > in bpf_arch_text_poke, so instead of splitting the function or adding new
> > > 'checkip' argument in previous version, it seems best to move the whole
> > > map_poke_run update as arch specific code.
> > > 
> > > [0] https://syzkaller.appspot.com/bug?extid=97a4fe20470e9bc30810
> > > 
> > > Cc: Lee Jones <lee@kernel.org>
> > > Cc: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> > > Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
> > > Reported-by: syzbot+97a4fe20470e9bc30810@syzkaller.appspotmail.com
> > > Acked-by: Yonghong Song <yonghong.song@linux.dev>
> > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > > ---
> > >  arch/x86/net/bpf_jit_comp.c | 46 +++++++++++++++++++++++++++++
> > >  include/linux/bpf.h         |  3 ++
> > >  kernel/bpf/arraymap.c       | 58 +++++++------------------------------
> > >  3 files changed, 59 insertions(+), 48 deletions(-)
> > 
> > Please could we have this backported?
> > 
> > Guided by the Fixes: tag.
> 
> <formletter>
> 
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
> 
> </formletter>

Apologies.

Commit ID: 4b7de801606e504e69689df71475d27e35336fb3
Subject:   bpf: Fix prog_array_map_poke_run map poke update
Reason:    Fixes a race condition in BPF.
Versions:  linux-5.10.y+, as specified by the Fixes: tag above

Thanks.

-- 
Lee Jones [李琼斯]