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Message-ID: <CAEyhmHQOeKmQZnq9RvaPANdLfcsAJX=xU+nL+p4=sPwcYPOfGw@mail.gmail.com>
Date: Mon, 4 Aug 2025 10:24:43 +0800
From: Hengqi Chen <hengqi.chen@...il.com>
To: Chenghao Duan <duanchenghao@...inos.cn>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
yangtiezhu@...ngson.cn, chenhuacai@...nel.org, martin.lau@...ux.dev,
eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
haoluo@...gle.com, jolsa@...nel.org, kernel@...0n.name,
linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev, bpf@...r.kernel.org,
guodongtai@...inos.cn, youling.tang@...ux.dev, jianghaoran@...inos.cn,
vincent.mc.li@...il.com, geliang@...nel.org
Subject: Re: [PATCH v5 3/5] LoongArch: BPF: Implement dynamic code
modification support
On Wed, Jul 30, 2025 at 9:13 PM Chenghao Duan <duanchenghao@...inos.cn> wrote:
>
> This commit adds support for BPF dynamic code modification on the
> LoongArch architecture.:
> 1. Implement bpf_arch_text_poke() for runtime instruction patching.
> 2. Add bpf_arch_text_copy() for instruction block copying.
> 3. Create bpf_arch_text_invalidate() for code invalidation.
>
> 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.
>
> larch_insn_text_copy is solely used for BPF. The use of
> larch_insn_text_copy() requires page_size alignment. Currently, only
> the size of the trampoline is page-aligned.
>
> Co-developed-by: George Guo <guodongtai@...inos.cn>
> Signed-off-by: George Guo <guodongtai@...inos.cn>
> Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
> ---
> arch/loongarch/include/asm/inst.h | 1 +
> arch/loongarch/kernel/inst.c | 27 ++++++++
> arch/loongarch/net/bpf_jit.c | 104 ++++++++++++++++++++++++++++++
> 3 files changed, 132 insertions(+)
>
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index 2ae96a35d..88bb73e46 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -497,6 +497,7 @@ void arch_simulate_insn(union loongarch_instruction insn, struct pt_regs *regs);
> int larch_insn_read(void *addr, u32 *insnp);
> int larch_insn_write(void *addr, u32 insn);
> int larch_insn_patch_text(void *addr, u32 insn);
> +int larch_insn_text_copy(void *dst, void *src, size_t len);
>
> u32 larch_insn_gen_nop(void);
> u32 larch_insn_gen_b(unsigned long pc, unsigned long dest);
> diff --git a/arch/loongarch/kernel/inst.c b/arch/loongarch/kernel/inst.c
> index 674e3b322..7df63a950 100644
> --- a/arch/loongarch/kernel/inst.c
> +++ b/arch/loongarch/kernel/inst.c
> @@ -4,6 +4,7 @@
> */
> #include <linux/sizes.h>
> #include <linux/uaccess.h>
> +#include <linux/set_memory.h>
>
> #include <asm/cacheflush.h>
> #include <asm/inst.h>
> @@ -218,6 +219,32 @@ int larch_insn_patch_text(void *addr, u32 insn)
> return ret;
> }
>
> +int larch_insn_text_copy(void *dst, void *src, size_t len)
> +{
> + int ret;
> + unsigned long flags;
> + unsigned long dst_start, dst_end, dst_len;
> +
> + dst_start = round_down((unsigned long)dst, PAGE_SIZE);
> + dst_end = round_up((unsigned long)dst + len, PAGE_SIZE);
> + dst_len = dst_end - dst_start;
> +
> + set_memory_rw(dst_start, dst_len / PAGE_SIZE);
> + raw_spin_lock_irqsave(&patch_lock, flags);
> +
> + ret = copy_to_kernel_nofault(dst, src, len);
> + if (ret)
> + pr_err("%s: operation failed\n", __func__);
> +
> + raw_spin_unlock_irqrestore(&patch_lock, flags);
> + set_memory_rox(dst_start, dst_len / PAGE_SIZE);
> +
> + if (!ret)
> + flush_icache_range((unsigned long)dst, (unsigned long)dst + len);
> +
> + return ret;
> +}
> +
> u32 larch_insn_gen_nop(void)
> {
> return INSN_NOP;
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index 7032f11d3..5e6ae7e0e 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -4,8 +4,12 @@
> *
> * Copyright (C) 2022 Loongson Technology Corporation Limited
> */
> +#include <linux/memory.h>
> #include "bpf_jit.h"
>
> +#define LOONGARCH_LONG_JUMP_NINSNS 5
> +#define LOONGARCH_LONG_JUMP_NBYTES (LOONGARCH_LONG_JUMP_NINSNS * 4)
> +
> #define REG_TCC LOONGARCH_GPR_A6
> #define TCC_SAVED LOONGARCH_GPR_S5
>
> @@ -88,6 +92,7 @@ static u8 tail_call_reg(struct jit_ctx *ctx)
> */
> static void build_prologue(struct jit_ctx *ctx)
> {
> + int i;
> int stack_adjust = 0, store_offset, bpf_stack_adjust;
>
> bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
> @@ -98,6 +103,10 @@ static void build_prologue(struct jit_ctx *ctx)
> stack_adjust = round_up(stack_adjust, 16);
> stack_adjust += bpf_stack_adjust;
>
> + /* Reserve space for the move_imm + jirl instruction */
> + for (i = 0; i < LOONGARCH_LONG_JUMP_NINSNS; i++)
> + emit_insn(ctx, nop);
> +
> /*
> * First instruction initializes the tail call count (TCC).
> * On tail call we skip this instruction, and the TCC is
> @@ -1367,3 +1376,98 @@ bool bpf_jit_supports_subprog_tailcalls(void)
> {
> return true;
> }
> +
> +static int emit_jump_and_link(struct jit_ctx *ctx, u8 rd, u64 target)
> +{
> + if (!target) {
> + pr_err("bpf_jit: jump target address is error\n");
> + return -EFAULT;
> + }
> +
> + 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)target);
> +}
> +
> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
> + void *old_addr, void *new_addr)
> +{
> + u32 old_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
> + u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[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, LOONGARCH_LONG_JUMP_NBYTES))
> + 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, LOONGARCH_LONG_JUMP_NBYTES))
> + ret = larch_insn_text_copy(ip, new_insns, LOONGARCH_LONG_JUMP_NBYTES);
> + mutex_unlock(&text_mutex);
The text_mutex and patch_lock inside larch_insn_text_copy() ONLY
prevent concurrent modifications.
You may need stop_machine() to prevent concurrent modifications/executions.
> + return ret;
> +}
> +
> +int bpf_arch_text_invalidate(void *dst, size_t len)
> +{
> + int i;
> + int ret = 0;
> + u32 *inst;
> +
> + inst = kvmalloc(len, GFP_KERNEL);
> + if (!inst)
> + return -ENOMEM;
> +
> + for (i = 0; i < (len/sizeof(u32)); i++)
> + inst[i] = INSN_BREAK;
> +
> + mutex_lock(&text_mutex);
> + if (larch_insn_text_copy(dst, inst, len))
> + ret = -EINVAL;
> + mutex_unlock(&text_mutex);
> +
> + kvfree(inst);
> + return ret;
> +}
> +
> +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> +{
> + int ret;
> +
> + mutex_lock(&text_mutex);
> + ret = larch_insn_text_copy(dst, src, len);
> + mutex_unlock(&text_mutex);
> + if (ret)
> + return ERR_PTR(-EINVAL);
> +
> + return dst;
> +}
> --
> 2.25.1
>
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