Re: [PATCH bpf 3/9] bpf: enable access to ax register also from verifier rewrite

[David Miller]

From: Daniel Borkmann <dan...@iogearbox.net>
Date: Tue,  1 Jan 2019 21:49:19 +0100

> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index a34312a..4e6f29a 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -858,6 +858,26 @@ static int bpf_jit_blind_insn(const struct bpf_insn 
> *from,
>       BUILD_BUG_ON(BPF_REG_AX  + 1 != MAX_BPF_JIT_REG);
>       BUILD_BUG_ON(MAX_BPF_REG + 1 != MAX_BPF_JIT_REG);
>  
> +     /* Constraints on AX register:
> +      *
> +      * AX register is inaccessible from user space. It is mapped in
> +      * all JITs, and used here for constant blinding rewrites. It is
> +      * typically "stateless" meaning its contents are only valid within
> +      * the executed instruction, but not across several instructions.
> +      * There are a few exceptions however which are further detailled
                                                                ^^^^^^^^^

Typo, should be "detailed".