netdev - Re: [PATCH v2 bpf-next 02/17] bpf: Add bpf_arch_text

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Date:   Thu, 7 Nov 2019 17:54:37 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Song Liu <songliubraving@...com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "x86@...nel.org" <x86@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 02/17] bpf: Add bpf_arch_text_poke() helper

On 11/7/19 9:50 AM, Alexei Starovoitov wrote:
> On Thu, Nov 7, 2019 at 9:20 AM Song Liu <songliubraving@...com> wrote:
>>
>>
>>
>>> On Nov 6, 2019, at 9:46 PM, Alexei Starovoitov <ast@...nel.org> wrote:
>>>
>>> Add bpf_arch_text_poke() helper that is used by BPF trampoline logic to patch
>>> nops/calls in kernel text into calls into BPF trampoline and to patch
>>> calls/nops inside BPF programs too.
>>>
>>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>>> ---
>>> arch/x86/net/bpf_jit_comp.c | 51 +++++++++++++++++++++++++++++++++++++
>>> include/linux/bpf.h         |  8 ++++++
>>> kernel/bpf/core.c           |  6 +++++
>>> 3 files changed, 65 insertions(+)
>>>
>>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>>> index 0399b1f83c23..8631d3bd637f 100644
>>> --- a/arch/x86/net/bpf_jit_comp.c
>>> +++ b/arch/x86/net/bpf_jit_comp.c
>>> @@ -9,9 +9,11 @@
>>> #include <linux/filter.h>
>>> #include <linux/if_vlan.h>
>>> #include <linux/bpf.h>
>>> +#include <linux/memory.h>
>>> #include <asm/extable.h>
>>> #include <asm/set_memory.h>
>>> #include <asm/nospec-branch.h>
>>> +#include <asm/text-patching.h>
>>>
>>> static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len)
>>> {
>>> @@ -487,6 +489,55 @@ static int emit_call(u8 **pprog, void *func, void *ip)
>>>        return 0;
>>> }
>>>
>>> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
>>> +                    void *old_addr, void *new_addr)
>>> +{
>>> +     u8 old_insn[NOP_ATOMIC5] = {};
>>> +     u8 new_insn[NOP_ATOMIC5] = {};
>>> +     u8 *prog;
>>> +     int ret;
>>> +
>>> +     if (!is_kernel_text((long)ip))
>>> +             /* BPF trampoline in modules is not supported */
>>> +             return -EINVAL;
>>> +
>>> +     if (old_addr) {
>>> +             prog = old_insn;
>>> +             ret = emit_call(&prog, old_addr, (void *)ip);
>>> +             if (ret)
>>> +                     return ret;
>>> +     }
>>> +     if (old_addr) {
>>                  ^ should be new_addr?
>>> +             prog = new_insn;
>>> +             ret = emit_call(&prog, old_addr, (void *)ip);
>>                                          ^^^ and here?
>>> +             if (ret)
>>> +                     return ret;
>>> +     }
>>> +     ret = -EBUSY;
>>> +     mutex_lock(&text_mutex);
>>> +     switch (t) {
>>> +     case BPF_MOD_NOP_TO_CALL:
>>> +             if (memcmp(ip, ideal_nops, 5))
>>
>> Maybe use X86_CALL_SIZE instead of 5? And the five more "5" below?
> 
> ohh. yes. of course. I had it fixed.
> NOP_ATOMIC5 above is incorrect as well. I had it fixed too.
> Looks like I've lost another squash commit last night.
> Sorry about that.

Argh. Now I see what happened.
I squashed it into patch 3 instead of patch 2. sorry.