ebpf vm

[laik]

虚拟机

eBPF 是一个 RISC 寄存器机，共有 11 个 64 位寄存虚拟机器，一个程序计数器和一个 512 字节固定大小的堆栈。九个寄存器是通用读写的，一个是只读堆栈指针，程序计数器是隐式的，即我们只能跳转到计数器的某个偏移量。VM 寄存器始终为 64 位宽（即使在 32 位 ARM 处理器内核中运行！）并且如果最高有效的 32 位为零，则支持 32 位子寄存器寻址 - 这将在第四部分在嵌入式设备上交叉编译和运行 eBPF 程序非常有用。

这些寄存器是：

r0： 存储函数调用和当前程序退出代码的返回值
r1 - r5： 作为函数调用的参数，在程序开始时 r1 包含上下文参数指针
r6 - r9： 这些在内核函数调用之间被保留
r10： 每个 eBPF 程序 512 字节堆栈的只读指针

在加载时提供的 eBPF 程序类型[2]准确地决定了哪些内核函数子集可以调用，以及在程序启动时通过 r1 提供的上下文参数。r0 中存储的程序退出值的含义也是由程序类型决定的。

每个函数调用在寄存器 r1 - r5 中最多可以有 5 个参数；这适用于 eBPF 到 eBPF 和内核函数的调用。寄存器 r1 - r5 只能存储数字或指向堆栈的指针（作为参数传递给函数），从不直接指向任意内存的指针。所有内存访问都必须先将数据加载到 eBPF 堆栈中，然后才能在 eBPF 程序中使用它。此限制有助于 eBPF 验证器，它简化了内存模型以实现更轻松的正确性检查。

BPF 可访问的内核“辅助”函数由内核核心（不可通过模块扩展）通过类似于定义系统调用的 API 定义，使用 BPF_CALL 宏。bpf.h定义试图为所有 BPF 可访问的内核“辅助”函数提供参考。例如 bpf_trace_printk 的定义使用 BPF_CALL_5 和 5 对类型/参数名称。定义参数数据类型很重要，因为在每个 eBPF 程序加载时，eBPF 验证器确保寄存器数据类型与被调用方参数类型匹配。

eBPF 指令也是固定大小的 64 位编码，大约 100 条指令（目前...）分为 8 类。VM 支持来自通用内存（ map 、堆栈、“上下文”如数据包缓冲区等）的 1 - 8 字节加载/存储、向前/向后（非）条件跳转、算术/逻辑运算和函数调用。如需深入了解操作码格式，请参阅 Cilium 项目指令集文档。IOVisor 项目还维护了一个有用的指令规范。

在本系列第一部分研究的示例中，我们使用了一些有用的内核宏来使用以下结构创建 eBPF 字节码指令数组（所有指令都以这种方式编码）：

struct bpf_insn {
 __u8 操作码；/* opcode */
 __u8 dst_reg:4; /* dest register */
 __u8 src_reg:4; /* source register */
 __s16 off; /* signed offset */
 __s32 imm; /* signed immediate constant */
};

msb                                                        lsb
+------------------------+----------------+----+----+--------+
|immediate               |offset          |src |dst |opcode  |
+------------------------+----------------+----+----+--------+
让我们看一下 BPF_JMP_IMM指令，它针对立即值对条件跳转进行编码。下面的宏注释对指令逻辑应该是不言自明的。操作码编码指令类 BPF_JMP 、操作（通过 BPF_OP 位域传递以确保正确性）和表示它是对立即数/常量值 BPF_K 的操作的标志进行编码。

#define BPF_OP(code) ((code) & 0xf0)
#define BPF_K 0x00

/* 针对立即数的条件跳转，if (dst_reg 'op' imm32) goto pc + off16 */

#define BPF_JMP_IMM(OP, DST, IMM, OFF) \
 ((struct bpf_insn) { \
  .code = BPF_JMP | BPF_OP(OP) | BPF_K, \
  .dst_reg = DST, \
  .src_reg = 0
  , \
  .off = OFF, \ .imm = IMM })

如果我们计算值或反汇编包含 BPF_JMP_IMM ( BPF_JEQ , BPF_REG_0 , 0 , 2 ) 的 eBPF 字节码二进制文件，我们会发现它是 0x020015 格式。这个特定的字节码非常频繁地用于测试存储在 r0 中的函数调用的返回值；如果 r0 == 0，它会跳过接下来的 2 条指令。

[laik]

vm 仿真代码

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdarg.h>
#include <inttypes.h>
#include <sys/mman.h>
#include "ubpf_int.h"

#define MAX_EXT_FUNCS 64

const char* ubpf_string_table[1] = {
    "uBPF error: division by zero at PC %u\n",
};

static bool validate(const struct ubpf_vm *vm, const struct ebpf_inst *insts, uint32_t num_insts, char **errmsg);
static bool bounds_check(const struct ubpf_vm *vm, void *addr, int size, const char *type, uint16_t cur_pc, void *mem, size_t mem_len, void *stack);

bool ubpf_toggle_bounds_check(struct ubpf_vm *vm, bool enable)
{
    bool old = vm->bounds_check_enabled;
    vm->bounds_check_enabled = enable;
    return old;
}

void ubpf_set_error_print(struct ubpf_vm *vm, int (*error_printf)(FILE* stream, const char* format, ...))
{
    if (error_printf)
        vm->error_printf = error_printf;
    else
        vm->error_printf = fprintf;
}

struct ubpf_vm *
ubpf_create(void)
{
    struct ubpf_vm *vm = calloc(1, sizeof(*vm));
    if (vm == NULL) {
        return NULL;
    }

    vm->ext_funcs = calloc(MAX_EXT_FUNCS, sizeof(*vm->ext_funcs));
    if (vm->ext_funcs == NULL) {
        ubpf_destroy(vm);
        return NULL;
    }

    vm->ext_func_names = calloc(MAX_EXT_FUNCS, sizeof(*vm->ext_func_names));
    if (vm->ext_func_names == NULL) {
        ubpf_destroy(vm);
        return NULL;
    }

    vm->bounds_check_enabled = true;
    vm->error_printf = fprintf;

    vm->unwind_stack_extension_index = -1;
    return vm;
}

void
ubpf_destroy(struct ubpf_vm *vm)
{
    ubpf_unload_code(vm);
    free(vm->ext_funcs);
    free(vm->ext_func_names);
    free(vm);
}

int
ubpf_register(struct ubpf_vm *vm, unsigned int idx, const char *name, void *fn)
{
    if (idx >= MAX_EXT_FUNCS) {
        return -1;
    }

    vm->ext_funcs[idx] = (ext_func)fn;
    vm->ext_func_names[idx] = name;

    return 0;
}

int ubpf_set_unwind_function_index(struct ubpf_vm *vm, unsigned int idx)
{
    if (vm->unwind_stack_extension_index != -1) {
        return -1;
    }

    vm->unwind_stack_extension_index = idx;
    return 0;
}

unsigned int
ubpf_lookup_registered_function(struct ubpf_vm *vm, const char *name)
{
    int i;
    for (i = 0; i < MAX_EXT_FUNCS; i++) {
        const char *other = vm->ext_func_names[i];
        if (other && !strcmp(other, name)) {
            return i;
        }
    }
    return -1;
}

int
ubpf_load(struct ubpf_vm *vm, const void *code, uint32_t code_len, char **errmsg)
{
    *errmsg = NULL;

    if (vm->insts) {
        *errmsg = ubpf_error("code has already been loaded into this VM. Use ubpf_unload_code() if you need to reuse this VM");
        return -1;
    }

    if (code_len % 8 != 0) {
        *errmsg = ubpf_error("code_len must be a multiple of 8");
        return -1;
    }

    if (!validate(vm, code, code_len/8, errmsg)) {
        return -1;
    }

    vm->insts = malloc(code_len);
    if (vm->insts == NULL) {
        *errmsg = ubpf_error("out of memory");
        return -1;
    }

    memcpy(vm->insts, code, code_len);
    vm->num_insts = code_len/sizeof(vm->insts[0]);

    return 0;
}

void
ubpf_unload_code(struct ubpf_vm *vm)
{
    if (vm->jitted) {
        munmap(vm->jitted, vm->jitted_size);
        vm->jitted = NULL;
        vm->jitted_size = 0;
    }
    if (vm->insts) {
        free(vm->insts);
        vm->insts = NULL;
        vm->num_insts = 0;
    }
}

static uint32_t
u32(uint64_t x)
{
    return x;
}

int 
ubpf_exec(const struct ubpf_vm *vm, void *mem, size_t mem_len, uint64_t* bpf_return_value)
{
    uint16_t pc = 0;
    const struct ebpf_inst *insts = vm->insts;
    uint64_t reg[16];
    uint64_t stack[(UBPF_STACK_SIZE+7)/8];

    if (!insts) {
        /* Code must be loaded before we can execute */
        return -1;
    }

    reg[1] = (uintptr_t)mem;
    reg[2] = (uint64_t)mem_len;
    reg[10] = (uintptr_t)stack + sizeof(stack);

    while (1) {
        const uint16_t cur_pc = pc;
        struct ebpf_inst inst = insts[pc++];

        switch (inst.opcode) {
        case EBPF_OP_ADD_IMM:
            reg[inst.dst] += inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_ADD_REG:
            reg[inst.dst] += reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_SUB_IMM:
            reg[inst.dst] -= inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_SUB_REG:
            reg[inst.dst] -= reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_MUL_IMM:
            reg[inst.dst] *= inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_MUL_REG:
            reg[inst.dst] *= reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_DIV_IMM:
            reg[inst.dst] = u32(reg[inst.dst]) / u32(inst.imm);
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_DIV_REG:
            if (reg[inst.src] == 0) {
                vm->error_printf(stderr, ubpf_string_table[UBPF_STRING_ID_DIVIDE_BY_ZERO], cur_pc);
                return -1;
            }
            reg[inst.dst] = u32(reg[inst.dst]) / u32(reg[inst.src]);
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_OR_IMM:
            reg[inst.dst] |= inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_OR_REG:
            reg[inst.dst] |= reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_AND_IMM:
            reg[inst.dst] &= inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_AND_REG:
            reg[inst.dst] &= reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_LSH_IMM:
            reg[inst.dst] <<= inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_LSH_REG:
            reg[inst.dst] <<= reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_RSH_IMM:
            reg[inst.dst] = u32(reg[inst.dst]) >> inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_RSH_REG:
            reg[inst.dst] = u32(reg[inst.dst]) >> reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_NEG:
            reg[inst.dst] = -(int64_t)reg[inst.dst];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_MOD_IMM:
            reg[inst.dst] = u32(reg[inst.dst]) % u32(inst.imm);
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_MOD_REG:
            if (reg[inst.src] == 0) {
                vm->error_printf(stderr, ubpf_string_table[UBPF_STRING_ID_DIVIDE_BY_ZERO], cur_pc);
                return -1;
            }
            reg[inst.dst] = u32(reg[inst.dst]) % u32(reg[inst.src]);
            break;
        case EBPF_OP_XOR_IMM:
            reg[inst.dst] ^= inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_XOR_REG:
            reg[inst.dst] ^= reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_MOV_IMM:
            reg[inst.dst] = inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_MOV_REG:
            reg[inst.dst] = reg[inst.src];
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_ARSH_IMM:
            reg[inst.dst] = (int32_t)reg[inst.dst] >> inst.imm;
            reg[inst.dst] &= UINT32_MAX;
            break;
        case EBPF_OP_ARSH_REG:
            reg[inst.dst] = (int32_t)reg[inst.dst] >> u32(reg[inst.src]);
            reg[inst.dst] &= UINT32_MAX;
            break;

        case EBPF_OP_LE:
            if (inst.imm == 16) {
                reg[inst.dst] = htole16(reg[inst.dst]);
            } else if (inst.imm == 32) {
                reg[inst.dst] = htole32(reg[inst.dst]);
            } else if (inst.imm == 64) {
                reg[inst.dst] = htole64(reg[inst.dst]);
            }
            break;
        case EBPF_OP_BE:
            if (inst.imm == 16) {
                reg[inst.dst] = htobe16(reg[inst.dst]);
            } else if (inst.imm == 32) {
                reg[inst.dst] = htobe32(reg[inst.dst]);
            } else if (inst.imm == 64) {
                reg[inst.dst] = htobe64(reg[inst.dst]);
            }
            break;

        case EBPF_OP_ADD64_IMM:
            reg[inst.dst] += inst.imm;
            break;
        case EBPF_OP_ADD64_REG:
            reg[inst.dst] += reg[inst.src];
            break;
        case EBPF_OP_SUB64_IMM:
            reg[inst.dst] -= inst.imm;
            break;
        case EBPF_OP_SUB64_REG:
            reg[inst.dst] -= reg[inst.src];
            break;
        case EBPF_OP_MUL64_IMM:
            reg[inst.dst] *= inst.imm;
            break;
        case EBPF_OP_MUL64_REG:
            reg[inst.dst] *= reg[inst.src];
            break;
        case EBPF_OP_DIV64_IMM:
            reg[inst.dst] /= inst.imm;
            break;
        case EBPF_OP_DIV64_REG:
            if (reg[inst.src] == 0) {
                vm->error_printf(stderr, ubpf_string_table[UBPF_STRING_ID_DIVIDE_BY_ZERO], cur_pc);
                return -1;
            }
            reg[inst.dst] /= reg[inst.src];
            break;
        case EBPF_OP_OR64_IMM:
            reg[inst.dst] |= inst.imm;
            break;
        case EBPF_OP_OR64_REG:
            reg[inst.dst] |= reg[inst.src];
            break;
        case EBPF_OP_AND64_IMM:
            reg[inst.dst] &= inst.imm;
            break;
        case EBPF_OP_AND64_REG:
            reg[inst.dst] &= reg[inst.src];
            break;
        case EBPF_OP_LSH64_IMM:
            reg[inst.dst] <<= inst.imm;
            break;
        case EBPF_OP_LSH64_REG:
            reg[inst.dst] <<= reg[inst.src];
            break;
        case EBPF_OP_RSH64_IMM:
            reg[inst.dst] >>= inst.imm;
            break;
        case EBPF_OP_RSH64_REG:
            reg[inst.dst] >>= reg[inst.src];
            break;
        case EBPF_OP_NEG64:
            reg[inst.dst] = -reg[inst.dst];
            break;
        case EBPF_OP_MOD64_IMM:
            reg[inst.dst] %= inst.imm;
            break;
        case EBPF_OP_MOD64_REG:
            if (reg[inst.src] == 0) {
                vm->error_printf(stderr, ubpf_string_table[UBPF_STRING_ID_DIVIDE_BY_ZERO], cur_pc);
                return -1;
            }
            reg[inst.dst] %= reg[inst.src];
            break;
        case EBPF_OP_XOR64_IMM:
            reg[inst.dst] ^= inst.imm;
            break;
        case EBPF_OP_XOR64_REG:
            reg[inst.dst] ^= reg[inst.src];
            break;
        case EBPF_OP_MOV64_IMM:
            reg[inst.dst] = inst.imm;
            break;
        case EBPF_OP_MOV64_REG:
            reg[inst.dst] = reg[inst.src];
            break;
        case EBPF_OP_ARSH64_IMM:
            reg[inst.dst] = (int64_t)reg[inst.dst] >> inst.imm;
            break;
        case EBPF_OP_ARSH64_REG:
            reg[inst.dst] = (int64_t)reg[inst.dst] >> reg[inst.src];
            break;

        /*
         * HACK runtime bounds check
         *
         * Needed since we don't have a verifier yet.
         */
#define BOUNDS_CHECK_LOAD(size) \
    do { \
        if (!bounds_check(vm, (char *)reg[inst.src] + inst.offset, size, "load", cur_pc, mem, mem_len, stack)) { \
            return -1; \
        } \
    } while (0)
#define BOUNDS_CHECK_STORE(size) \
    do { \
        if (!bounds_check(vm, (char *)reg[inst.dst] + inst.offset, size, "store", cur_pc, mem, mem_len, stack)) { \
            return -1; \
        } \
    } while (0)

        case EBPF_OP_LDXW:
            BOUNDS_CHECK_LOAD(4);
            reg[inst.dst] = *(uint32_t *)(uintptr_t)(reg[inst.src] + inst.offset);
            break;
        case EBPF_OP_LDXH:
            BOUNDS_CHECK_LOAD(2);
            reg[inst.dst] = *(uint16_t *)(uintptr_t)(reg[inst.src] + inst.offset);
            break;
        case EBPF_OP_LDXB:
            BOUNDS_CHECK_LOAD(1);
            reg[inst.dst] = *(uint8_t *)(uintptr_t)(reg[inst.src] + inst.offset);
            break;
        case EBPF_OP_LDXDW:
            BOUNDS_CHECK_LOAD(8);
            reg[inst.dst] = *(uint64_t *)(uintptr_t)(reg[inst.src] + inst.offset);
            break;

        case EBPF_OP_STW:
            BOUNDS_CHECK_STORE(4);
            *(uint32_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = inst.imm;
            break;
        case EBPF_OP_STH:
            BOUNDS_CHECK_STORE(2);
            *(uint16_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = inst.imm;
            break;
        case EBPF_OP_STB:
            BOUNDS_CHECK_STORE(1);
            *(uint8_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = inst.imm;
            break;
        case EBPF_OP_STDW:
            BOUNDS_CHECK_STORE(8);
            *(uint64_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = inst.imm;
            break;

        case EBPF_OP_STXW:
            BOUNDS_CHECK_STORE(4);
            *(uint32_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = reg[inst.src];
            break;
        case EBPF_OP_STXH:
            BOUNDS_CHECK_STORE(2);
            *(uint16_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = reg[inst.src];
            break;
        case EBPF_OP_STXB:
            BOUNDS_CHECK_STORE(1);
            *(uint8_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = reg[inst.src];
            break;
        case EBPF_OP_STXDW:
            BOUNDS_CHECK_STORE(8);
            *(uint64_t *)(uintptr_t)(reg[inst.dst] + inst.offset) = reg[inst.src];
            break;

        case EBPF_OP_LDDW:
            reg[inst.dst] = (uint32_t)inst.imm | ((uint64_t)insts[pc++].imm << 32);
            break;

        case EBPF_OP_JA:
            pc += inst.offset;
            break;
        case EBPF_OP_JEQ_IMM:
            if (reg[inst.dst] == inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JEQ_REG:
            if (reg[inst.dst] == reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JGT_IMM:
            if (reg[inst.dst] > (uint32_t)inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JGT_REG:
            if (reg[inst.dst] > reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JGE_IMM:
            if (reg[inst.dst] >= (uint32_t)inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JGE_REG:
            if (reg[inst.dst] >= reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JLT_IMM:
            if (reg[inst.dst] < (uint32_t)inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JLT_REG:
            if (reg[inst.dst] < reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JLE_IMM:
            if (reg[inst.dst] <= (uint32_t)inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JLE_REG:
            if (reg[inst.dst] <= reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSET_IMM:
            if (reg[inst.dst] & inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSET_REG:
            if (reg[inst.dst] & reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JNE_IMM:
            if (reg[inst.dst] != inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JNE_REG:
            if (reg[inst.dst] != reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSGT_IMM:
            if ((int64_t)reg[inst.dst] > inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSGT_REG:
            if ((int64_t)reg[inst.dst] > (int64_t)reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSGE_IMM:
            if ((int64_t)reg[inst.dst] >= inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSGE_REG:
            if ((int64_t)reg[inst.dst] >= (int64_t)reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSLT_IMM:
            if ((int64_t)reg[inst.dst] < inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSLT_REG:
            if ((int64_t)reg[inst.dst] < (int64_t)reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSLE_IMM:
            if ((int64_t)reg[inst.dst] <= inst.imm) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_JSLE_REG:
            if ((int64_t)reg[inst.dst] <= (int64_t)reg[inst.src]) {
                pc += inst.offset;
            }
            break;
        case EBPF_OP_EXIT:
            *bpf_return_value = reg[0];
            return 0;
        case EBPF_OP_CALL:
            reg[0] = vm->ext_funcs[inst.imm](reg[1], reg[2], reg[3], reg[4], reg[5]);
            // Unwind the stack if unwind extension returns success.
            if (inst.imm == vm->unwind_stack_extension_index && reg[0] == 0) {
                *bpf_return_value = reg[0];
                return 0;
            }
            break;
        }
    }
}

static bool
validate(const struct ubpf_vm *vm, const struct ebpf_inst *insts, uint32_t num_insts, char **errmsg)
{
    if (num_insts >= UBPF_MAX_INSTS) {
        *errmsg = ubpf_error("too many instructions (max %u)", UBPF_MAX_INSTS);
        return false;
    }

    int i;
    for (i = 0; i < num_insts; i++) {
        struct ebpf_inst inst = insts[i];
        bool store = false;

        switch (inst.opcode) {
        case EBPF_OP_ADD_IMM:
        case EBPF_OP_ADD_REG:
        case EBPF_OP_SUB_IMM:
        case EBPF_OP_SUB_REG:
        case EBPF_OP_MUL_IMM:
        case EBPF_OP_MUL_REG:
        case EBPF_OP_DIV_REG:
        case EBPF_OP_OR_IMM:
        case EBPF_OP_OR_REG:
        case EBPF_OP_AND_IMM:
        case EBPF_OP_AND_REG:
        case EBPF_OP_LSH_IMM:
        case EBPF_OP_LSH_REG:
        case EBPF_OP_RSH_IMM:
        case EBPF_OP_RSH_REG:
        case EBPF_OP_NEG:
        case EBPF_OP_MOD_REG:
        case EBPF_OP_XOR_IMM:
        case EBPF_OP_XOR_REG:
        case EBPF_OP_MOV_IMM:
        case EBPF_OP_MOV_REG:
        case EBPF_OP_ARSH_IMM:
        case EBPF_OP_ARSH_REG:
            break;

        case EBPF_OP_LE:
        case EBPF_OP_BE:
            if (inst.imm != 16 && inst.imm != 32 && inst.imm != 64) {
                *errmsg = ubpf_error("invalid endian immediate at PC %d", i);
                return false;
            }
            break;

        case EBPF_OP_ADD64_IMM:
        case EBPF_OP_ADD64_REG:
        case EBPF_OP_SUB64_IMM:
        case EBPF_OP_SUB64_REG:
        case EBPF_OP_MUL64_IMM:
        case EBPF_OP_MUL64_REG:
        case EBPF_OP_DIV64_REG:
        case EBPF_OP_OR64_IMM:
        case EBPF_OP_OR64_REG:
        case EBPF_OP_AND64_IMM:
        case EBPF_OP_AND64_REG:
        case EBPF_OP_LSH64_IMM:
        case EBPF_OP_LSH64_REG:
        case EBPF_OP_RSH64_IMM:
        case EBPF_OP_RSH64_REG:
        case EBPF_OP_NEG64:
        case EBPF_OP_MOD64_REG:
        case EBPF_OP_XOR64_IMM:
        case EBPF_OP_XOR64_REG:
        case EBPF_OP_MOV64_IMM:
        case EBPF_OP_MOV64_REG:
        case EBPF_OP_ARSH64_IMM:
        case EBPF_OP_ARSH64_REG:
            break;

        case EBPF_OP_LDXW:
        case EBPF_OP_LDXH:
        case EBPF_OP_LDXB:
        case EBPF_OP_LDXDW:
            break;

        case EBPF_OP_STW:
        case EBPF_OP_STH:
        case EBPF_OP_STB:
        case EBPF_OP_STDW:
        case EBPF_OP_STXW:
        case EBPF_OP_STXH:
        case EBPF_OP_STXB:
        case EBPF_OP_STXDW:
            store = true;
            break;

        case EBPF_OP_LDDW:
            if (i + 1 >= num_insts || insts[i+1].opcode != 0) {
                *errmsg = ubpf_error("incomplete lddw at PC %d", i);
                return false;
            }
            i++; /* Skip next instruction */
            break;

        case EBPF_OP_JA:
        case EBPF_OP_JEQ_REG:
        case EBPF_OP_JEQ_IMM:
        case EBPF_OP_JGT_REG:
        case EBPF_OP_JGT_IMM:
        case EBPF_OP_JGE_REG:
        case EBPF_OP_JGE_IMM:
        case EBPF_OP_JLT_REG:
        case EBPF_OP_JLT_IMM:
        case EBPF_OP_JLE_REG:
        case EBPF_OP_JLE_IMM:
        case EBPF_OP_JSET_REG:
        case EBPF_OP_JSET_IMM:
        case EBPF_OP_JNE_REG:
        case EBPF_OP_JNE_IMM:
        case EBPF_OP_JSGT_IMM:
        case EBPF_OP_JSGT_REG:
        case EBPF_OP_JSGE_IMM:
        case EBPF_OP_JSGE_REG:
        case EBPF_OP_JSLT_IMM:
        case EBPF_OP_JSLT_REG:
        case EBPF_OP_JSLE_IMM:
        case EBPF_OP_JSLE_REG:
            if (inst.offset == -1) {
                *errmsg = ubpf_error("infinite loop at PC %d", i);
                return false;
            }
            int new_pc = i + 1 + inst.offset;
            if (new_pc < 0 || new_pc >= num_insts) {
                *errmsg = ubpf_error("jump out of bounds at PC %d", i);
                return false;
            } else if (insts[new_pc].opcode == 0) {
                *errmsg = ubpf_error("jump to middle of lddw at PC %d", i);
                return false;
            }
            break;

        case EBPF_OP_CALL:
            if (inst.imm < 0 || inst.imm >= MAX_EXT_FUNCS) {
                *errmsg = ubpf_error("invalid call immediate at PC %d", i);
                return false;
            }
            if (!vm->ext_funcs[inst.imm]) {
                *errmsg = ubpf_error("call to nonexistent function %u at PC %d", inst.imm, i);
                return false;
            }
            break;

        case EBPF_OP_EXIT:
            break;

        case EBPF_OP_DIV_IMM:
        case EBPF_OP_MOD_IMM:
        case EBPF_OP_DIV64_IMM:
        case EBPF_OP_MOD64_IMM:
            if (inst.imm == 0) {
                *errmsg = ubpf_error("division by zero at PC %d", i);
                return false;
            }
            break;

        default:
            *errmsg = ubpf_error("unknown opcode 0x%02x at PC %d", inst.opcode, i);
            return false;
        }

        if (inst.src > 10) {
            *errmsg = ubpf_error("invalid source register at PC %d", i);
            return false;
        }

        if (inst.dst > 9 && !(store && inst.dst == 10)) {
            *errmsg = ubpf_error("invalid destination register at PC %d", i);
            return false;
        }
    }

    return true;
}

static bool
bounds_check(const struct ubpf_vm *vm, void *addr, int size, const char *type, uint16_t cur_pc, void *mem, size_t mem_len, void *stack)
{
    if (!vm->bounds_check_enabled)
        return true;
    if (mem && (addr >= mem && ((char*)addr + size) <= ((char*)mem + mem_len))) {
        /* Context access */
        return true;
    } else if (addr >= stack && ((char*)addr + size) <= ((char*)stack + UBPF_STACK_SIZE)) {
        /* Stack access */
        return true;
    } else {
        vm->error_printf(stderr, "uBPF error: out of bounds memory %s at PC %u, addr %p, size %d\nmem %p/%zd stack %p/%d\n", type, cur_pc, addr, size, mem, mem_len, stack, UBPF_STACK_SIZE);
        return false;
    }
}

char *
ubpf_error(const char *fmt, ...)
{
    char *msg;
    va_list ap;
    va_start(ap, fmt);
    if (vasprintf(&msg, fmt, ap) < 0) {
        msg = NULL;
    }
    va_end(ap);
    return msg;
}