Messages in this thread | | | Date | Thu, 22 Aug 2019 00:42:12 +0530 | From | "Naveen N. Rao" <> | Subject | Re: Regression fix for bpf in v5.3 (was Re: [RFC PATCH] bpf: handle 32-bit zext during constant blinding) |
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Jiong Wang wrote: > > Michael Ellerman writes: > >> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes: >>> Since BPF constant blinding is performed after the verifier pass, there >>> are certain ALU32 instructions inserted which don't have a corresponding >>> zext instruction inserted after. This is causing a kernel oops on >>> powerpc and can be reproduced by running 'test_cgroup_storage' with >>> bpf_jit_harden=2. >>> >>> Fix this by emitting BPF_ZEXT during constant blinding if >>> prog->aux->verifier_zext is set. >>> >>> Fixes: a4b1d3c1ddf6cb ("bpf: verifier: insert zero extension according to analysis result") >>> Reported-by: Michael Ellerman <mpe@ellerman.id.au> >>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> >>> --- >>> This approach (the location where zext is being introduced below, in >>> particular) works for powerpc, but I am not entirely sure if this is >>> sufficient for other architectures as well. This is broken on v5.3-rc4. >> >> Any comment on this? > > Have commented on https://marc.info/?l=linux-netdev&m=156637836024743&w=2 > > The fix looks correct to me on "BPF_LD | BPF_IMM | BPF_DW", but looks > unnecessary on two other places. It would be great if you or Naveen could > confirm it.
Jiong, Thanks for the review. I can now see why the other two changes are not necessary. I will post a follow-on patch.
Thanks! - Naveen
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