On Tue, Jun 21, 2016 at 09:15:48PM +1000, Michael Ellerman wrote: > On Tue, 2016-06-21 at 14:28 +0530, Naveen N. Rao wrote: > > On 2016/06/20 03:56PM, Thadeu Lima de Souza Cascardo wrote: > > > On Sun, Jun 19, 2016 at 11:19:14PM +0530, Naveen N. Rao wrote: > > > > On 2016/06/17 10:00AM, Thadeu Lima de Souza Cascardo wrote: > > > > > > > > > > Hi, Michael and Naveen. > > > > > > > > > > I noticed independently that there is a problem with BPF JIT and > > > > > ABIv2, and > > > > > worked out the patch below before I noticed Naveen's patchset and the > > > > > latest > > > > > changes in ppc tree for a better way to check for ABI versions. > > > > > > > > > > However, since the issue described below affect mainline and stable > > > > > kernels, > > > > > would you consider applying it before merging your two patchsets, so > > > > > that we can > > > > > more easily backport the fix? > > > > > > > > Hi Cascardo, > > > > Given that this has been broken on ABIv2 since forever, I didn't bother > > > > fixing it. But, I can see why this would be a good thing to have for > > > > -stable and existing distros. However, while your patch below may fix > > > > the crash you're seeing on ppc64le, it is not sufficient -- you'll need > > > > changes in bpf_jit_asm.S as well. > > > > > > Hi, Naveen. > > > > > > Any tips on how to exercise possible issues there? Or what changes you > > > think > > > would be sufficient? > > > > The calling convention is different with ABIv2 and so we'll need changes > > in bpf_slow_path_common() and sk_negative_common(). > > How big would those changes be? Do we know? > > How come no one reported this was broken previously? This is the first I've > heard of it being broken. >
I just heard of it less than two weeks ago, and only could investigate it last week, when I realized mainline was also affected. It looks like the little-endian support for classic JIT were done before the conversion to ABIv2. And as JIT is disabled by default, no one seems to have exercised it. > > However, rather than enabling classic JIT for ppc64le, are we better off > > just disabling it? > > > > --- a/arch/powerpc/Kconfig > > +++ b/arch/powerpc/Kconfig > > @@ -128,7 +128,7 @@ config PPC > > select IRQ_FORCED_THREADING > > select HAVE_RCU_TABLE_FREE if SMP > > select HAVE_SYSCALL_TRACEPOINTS > > - select HAVE_CBPF_JIT > > + select HAVE_CBPF_JIT if CPU_BIG_ENDIAN > > select HAVE_ARCH_JUMP_LABEL > > select ARCH_HAVE_NMI_SAFE_CMPXCHG > > select ARCH_HAS_GCOV_PROFILE_ALL > > > > > > Michael, > > Let me know your thoughts on whether you intend to take this patch or > > Cascardo's patch for -stable before the eBPF patches. I can redo my > > patches accordingly. > > This patch sounds like the best option at the moment for something we can > backport. Unless the changes to fix it are minimal. > > cheers > With my patch only, I can run a minimal tcpdump tcp port 22 with success. It correctly filter packets. But as pointed out, slow paths may not be taken. I don't have strong opinions on what to apply to stable, just that it would be nice to have something for the crash before applying all the nice changes by Naveen. Cascardo.
