[RFC PATCH] bpf: handle 32-bit zext during constant blinding

[Naveen N. Rao]

Naveen N. Rao wrote:
> 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 at ellerman.id.au>
> Signed-off-by: Naveen N. Rao <naveen.n.rao at 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.

Alexie, Daniel, Jiong,
Any feedback on this?

- Naveen