Jiong Wang wrote:
Michael Ellerman writes:
"Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
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
