lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 22 Nov 2019 22:18:07 -0800 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, john fastabend <john.fastabend@...il.com>, Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org> Subject: Re: [PATCH bpf-next v2 7/8] bpf, x86: emit patchable direct jump as tail call On Fri, Nov 22, 2019 at 09:00:35PM -0800, Andrii Nakryiko wrote: > On Fri, Nov 22, 2019 at 6:28 PM Alexei Starovoitov > <alexei.starovoitov@...il.com> wrote: > > > > On Fri, Nov 22, 2019 at 3:25 PM Daniel Borkmann <daniel@...earbox.net> wrote: > > > >> + case BPF_MOD_CALL_TO_NOP: > > > >> + case BPF_MOD_JUMP_TO_NOP: > > > >> + if (old_addr && !new_addr) { > > > >> + memcpy(new_insn, nop_insn, X86_PATCH_SIZE); > > > >> + > > > >> + prog = old_insn; > > > >> + ret = emit_patch_fn(&prog, old_addr, ip); > > > >> + if (ret) > > > >> + return ret; > > > >> + break; > > > >> + } > > > >> + return -ENXIO; > > > >> + default: > > > > > > > > There is this redundancy between BPF_MOD_xxx enums and > > > > old_addr+new_addr (both encode what kind of transition it is), which > > > > leads to this cumbersome logic. Would it be simpler to have > > > > old_addr/new_addr determine whether it's X-to-NOP, NOP-to-Y, or X-to-Y > > > > transition, while separate bool or simple BPF_MOD_CALL/BPF_MOD_JUMP > > > > enum determining whether it's a call or a jump that we want to update. > > > > Seems like that should be a simpler interface overall and cleaner > > > > implementation? > > > > > > Right we can probably simplify it further, I kept preserving the original > > > switch from Alexei's code where my assumption was that having the transition > > > explicitly spelled out was preferred in here and then based on that doing > > > the sanity checks to make sure we don't get bad input from any call-site > > > since we're modifying kernel text, e.g. in the bpf_trampoline_update() as > > > one example the BPF_MOD_* is a fixed constant input there. > > > > I guess we can try adding one more argument > > bpf_arch_text_poke(ip, BPF_MOD_NOP, old_addr, BPF_MOD_INTO_CALL, new_addr); > > I was thinking along the lines of: > > bpf_arch_text_poke(ip, BPF_MOD_CALL (or BPF_MOD_JMP), old_addr, new_addr); > > old_addr/new_addr being possibly NULL determine NOP/not-a-NOP. I see. Something like: if (BPF_MOD_CALL) { if (old_addr) memcmp(ip, old_call_insn); else memcmp(ip, nop_insn); } else if (BPF_MOD_JMP) { if (old_addr) memcmp(ip, old_jmp_insn); else memcmp(ip, nop_insn); } I guess that can work.
Powered by blists - more mailing lists