Jiong Wang wrote:
Naveen N. Rao writes:
Since BPF constant blinding is performed after the verifier pass, the
ALU32 instructions inserted for doubleword immediate loads don't have a
corresponding zext instruction. 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>
Thanks for the fix.
Reviewed-by: Jiong Wang <jiong.wang@xxxxxxxxxxxxx>
Just two other comments during review in case I am wrong on somewhere.
- Use verifier_zext instead of bpf_jit_needs_zext() seems better, even
though the latter could avoid extending function argument.
Because JIT back-ends look at verifier_zext, true means zext inserted
by verifier so JITs won't do the code-gen.
Use verifier_zext is sort of keeping JIT blinding the same behaviour
has verifier even though blinding doesn't belong to verifier, but for
such insn patching, it could be seen as a extension of verifier,
therefore use verifier_zext seems better than bpf_jit_needs_zext() to
me.
- JIT blinding is also escaping the HI32 randomization which happens
inside verifier, otherwise x86-64 regression should have caught this issue.
Jiong,
Thanks for the review.
Alexei, Daniel,
Can you please pick this up for v5.3. This is a regression and is
causing a crash on powerpc.
- Naveen
