On Mon, Aug 25, 2014 at 6:35 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote: > On Mon, Aug 25, 2014 at 6:06 PM, David Miller <davem@xxxxxxxxxxxxx> wrote: >> From: Alexei Starovoitov <ast@xxxxxxxxxxxx> >> Date: Mon, 25 Aug 2014 18:00:53 -0700 >> >>> add BPF_LD_IMM64 instruction to load 64-bit immediate value into a register. >> >> I think you need to rethink this. >> >> I understand that you want to be able to compile arbitrary C code into >> eBPF, but you have to restrict strongly what data the eBPF code can get >> to. > > I believe verifier already does restrict it. I don't see any holes in > the architecture. I'm probably not explaining it clearly though :( > >> Arbitrary pointer loads is asking for trouble. > > Of course. > There is no arbitrary pointer from user space. > Verifier checks all pointers. > I guess this commit log description is confusing. > It says: > BPF_LD_IMM64(R1, const_imm_map_ptr) > that's what appears in the program _after_ it goes through verifier. > User space cannot pass a pointer into the kernel. If you don't intend for userspace to load a program that contains this instruction, then why does it need to be an instruction that the verifier rewrites? Why not have an instruction "load immediate relocated pointer" that contains a reference to a relocation table and have the JIT do it? That might be easier to understand than having the verifier do it, and it'll avoid committing to ABIs before we need them. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
