Re: [PATCH RFC net-next 08/14] bpf: add eBPF verifier

[Chema Gonzalez]

On Wed, Jul 2, 2014 at 4:04 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
>>> +       reg = regs + BPF_REG_1; /* 1st arg to a function */
>>> +       reg->ptr = PTR_TO_CTX;
>> Wait, doesn't this depend on doing "BPF_MOV64_REG(BPF_REG_CTX,
>> BPF_REG_ARG1)" (the bpf-to-ebpf prologue), which is only enforced on
>> filters converted from bpf? In fact, shouldn't this set
>> regs[BPF_REG_CTX] instead of regs[BPF_REG_1] ?
>
> nope. it's REG_1.
> as you said r6=r1 is only emitted by converted classic filters.
> Verifier will see this 'r6=r1' assignment and will copy the r1 type into r6.
You're right. I read BPF_MOV64_REG() AT&T-syntax-style.

BTW, check_stack_write() in kernel/bpf/verifier.c has a couple of
assignments of a slot->ptr to 0 (instead of INVALID_PTR). I assume
this is unintended.

-Chema
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