Re: [PATCH v2 bpf-next 02/17] bpf: Add bpf_arch_text_poke() helper

On Thu, Nov 7, 2019 at 9:20 AM Song Liu [off-list ref] wrote:

quoted

On Nov 6, 2019, at 9:46 PM, Alexei Starovoitov [off-list ref] 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@kernel.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?

quoted

+             prog = new_insn;
+             ret = emit_call(&prog, old_addr, (void *)ip);

                                        ^^^ and here?

quoted

+             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.