[PATCH v2 2/4] LoongArch: BPF: Add bpf_arch_text_poke support for Loongarch

[Chenghao Duan <duanchenghao@xxxxxxxxxx>]

Implement the bpf_arch_text_poke function for the LoongArch
architecture. On LoongArch, since symbol addresses in the direct mapping
region cannot be reached via relative jump instructions from the paged
mapping region, we use the move_imm+jirl instruction pair as absolute
jump instructions. These require 2-5 instructions, so we reserve 5 NOP
instructions in the program as placeholders for function jumps.

Co-developed-by: George Guo <guodongtai@xxxxxxxxxx>
Signed-off-by: George Guo <guodongtai@xxxxxxxxxx>
Signed-off-by: Chenghao Duan <duanchenghao@xxxxxxxxxx>
---
 arch/loongarch/net/bpf_jit.c | 62 ++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index fa1500d4a..24332c596 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -4,6 +4,7 @@
  *
  * Copyright (C) 2022 Loongson Technology Corporation Limited
  */
+#include <linux/memory.h>
 #include "bpf_jit.h"
 
 #define REG_TCC		LOONGARCH_GPR_A6
@@ -1359,3 +1360,64 @@ bool bpf_jit_supports_subprog_tailcalls(void)
 {
 	return true;
 }
+
+static int emit_jump_and_link(struct jit_ctx *ctx, u8 rd, u64 ip, u64 target)
+{
+	s64 offset = (s64)(target - ip);
+
+	if (offset && (offset >= -SZ_128M && offset < SZ_128M)) {
+		emit_insn(ctx, bl, offset >> 2);
+	} else {
+		move_imm(ctx, LOONGARCH_GPR_T1, target, false);
+		emit_insn(ctx, jirl, rd, LOONGARCH_GPR_T1, 0);
+	}
+
+	return 0;
+}
+
+static int gen_jump_or_nops(void *target, void *ip, u32 *insns, bool is_call)
+{
+	struct jit_ctx ctx;
+
+	ctx.idx = 0;
+	ctx.image = (union loongarch_instruction *)insns;
+
+	if (!target) {
+		emit_insn((&ctx), nop);
+		emit_insn((&ctx), nop);
+		return 0;
+	}
+
+	return emit_jump_and_link(&ctx, is_call ? LOONGARCH_GPR_T0 : LOONGARCH_GPR_ZERO,
+				  (unsigned long)ip, (unsigned long)target);
+}
+
+int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
+		       void *old_addr, void *new_addr)
+{
+	u32 old_insns[5] = {[0 ... 4] = INSN_NOP};
+	u32 new_insns[5] = {[0 ... 4] = INSN_NOP};
+	bool is_call = poke_type == BPF_MOD_CALL;
+	int ret;
+
+	if (!is_kernel_text((unsigned long)ip) &&
+		!is_bpf_text_address((unsigned long)ip))
+		return -ENOTSUPP;
+
+	ret = gen_jump_or_nops(old_addr, ip, old_insns, is_call);
+	if (ret)
+		return ret;
+
+	if (memcmp(ip, old_insns, 5 * 4))
+		return -EFAULT;
+
+	ret = gen_jump_or_nops(new_addr, ip, new_insns, is_call);
+	if (ret)
+		return ret;
+
+	mutex_lock(&text_mutex);
+	if (memcmp(ip, new_insns, 5 * 4))
+		ret = larch_insn_text_copy(ip, new_insns, 5 * 4);
+	mutex_unlock(&text_mutex);
+	return ret;
+}
-- 
2.43.0