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

On Wed, Jul 2, 2014 at 4:35 PM, Chema Gonzalez [off-list ref] wrote:

On Wed, Jul 2, 2014 at 4:04 PM, Alexei Starovoitov [off-list ref] wrote:

quoted

quoted

quoted

+       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.

yes. good catch. Will fix it.
Too bad C compiler silently casts integers to enums