1 /* 2 * Copyright 2016, The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 // A brief overview of APF: 18 // 19 // APF machine is composed of: 20 // 1. A read-only program consisting of bytecodes as described below. 21 // 2. Two 32-bit registers, called R0 and R1. 22 // 3. Sixteen 32-bit memory slots. 23 // 4. A read-only packet. 24 // The program is executed by the interpreter below and parses the packet 25 // to determine if the application processor (AP) should be woken up to 26 // handle the packet or if can be dropped. 27 // 28 // APF bytecode description: 29 // 30 // The APF interpreter uses big-endian byte order for loads from the packet 31 // and for storing immediates in instructions. 32 // 33 // Each instruction starts with a byte composed of: 34 // Top 5 bits form "opcode" field, see *_OPCODE defines below. 35 // Next 2 bits form "size field", which indicate the length of an immediate 36 // value which follows the first byte. Values in this field: 37 // 0 => immediate value is 0 and no bytes follow. 38 // 1 => immediate value is 1 byte big. 39 // 2 => immediate value is 2 bytes big. 40 // 3 => immediate value is 4 bytes big. 41 // Bottom bit forms "register" field, which indicates which register this 42 // instruction operates on. 43 // 44 // There are three main categories of instructions: 45 // Load instructions 46 // These instructions load byte(s) of the packet into a register. 47 // They load either 1, 2 or 4 bytes, as determined by the "opcode" field. 48 // They load into the register specified by the "register" field. 49 // The immediate value that follows the first byte of the instruction is 50 // the byte offset from the begining of the packet to load from. 51 // There are "indexing" loads which add the value in R1 to the byte offset 52 // to load from. The "opcode" field determines which loads are "indexing". 53 // Arithmetic instructions 54 // These instructions perform simple operations, like addition, on register 55 // values. The result of these instructions is always written into R0. One 56 // argument of the arithmetic operation is R0's value. The other argument 57 // of the arithmetic operation is determined by the "register" field: 58 // If the "register" field is 0 then the immediate value following 59 // the first byte of the instruction is used as the other argument 60 // to the arithmetic operation. 61 // If the "register" field is 1 then R1's value is used as the other 62 // argument to the arithmetic operation. 63 // Conditional jump instructions 64 // These instructions compare register R0's value with another value, and if 65 // the comparison succeeds, jump (i.e. adjust the program counter). The 66 // immediate value that follows the first byte of the instruction 67 // represents the jump target offset, i.e. the value added to the program 68 // counter if the comparison succeeds. The other value compared is 69 // determined by the "register" field: 70 // If the "register" field is 0 then another immediate value 71 // follows the jump target offset. This immediate value is of the 72 // same size as the jump target offset, and represents the value 73 // to compare against. 74 // If the "register" field is 1 then register R1's value is 75 // compared against. 76 // The type of comparison (e.g. equal to, greater than etc) is determined 77 // by the "opcode" field. The comparison interprets both values being 78 // compared as unsigned values. 79 // 80 // Miscellaneous details: 81 // 82 // Pre-filled memory slot values 83 // When the APF program begins execution, three of the sixteen memory slots 84 // are pre-filled by the interpreter with values that may be useful for 85 // programs: 86 // Slot #13 is filled with the IPv4 header length. This value is calculated 87 // by loading the first byte of the IPv4 header and taking the 88 // bottom 4 bits and multiplying their value by 4. This value is 89 // set to zero if the first 4 bits after the link layer header are 90 // not 4, indicating not IPv4. 91 // Slot #14 is filled with size of the packet in bytes, including the 92 // link-layer header if any. 93 // Slot #15 is filled with the filter age in seconds. This is the number of 94 // seconds since the AP send the program to the chipset. This may 95 // be used by filters that should have a particular lifetime. For 96 // example, it can be used to rate-limit particular packets to one 97 // every N seconds. 98 // Special jump targets: 99 // When an APF program executes a jump to the byte immediately after the last 100 // byte of the progam (i.e., one byte past the end of the program), this 101 // signals the program has completed and determined the packet should be 102 // passed to the AP. 103 // When an APF program executes a jump two bytes past the end of the program, 104 // this signals the program has completed and determined the packet should 105 // be dropped. 106 // Jump if byte sequence doesn't match: 107 // This is a special instruction to facilitate matching long sequences of 108 // bytes in the packet. Initially it is encoded like a conditional jump 109 // instruction with two exceptions: 110 // The first byte of the instruction is always followed by two immediate 111 // fields: The first immediate field is the jump target offset like other 112 // conditional jump instructions. The second immediate field specifies the 113 // number of bytes to compare. 114 // These two immediate fields are followed by a sequence of bytes. These 115 // bytes are compared with the bytes in the packet starting from the 116 // position specified by the value of the register specified by the 117 // "register" field of the instruction. 118 119 // Number of memory slots, see ldm/stm instructions. 120 #define MEMORY_ITEMS 16 121 // Upon program execution starting some memory slots are prefilled: 122 #define MEMORY_OFFSET_IPV4_HEADER_SIZE 13 // 4*([APF_FRAME_HEADER_SIZE]&15) 123 #define MEMORY_OFFSET_PACKET_SIZE 14 // Size of packet in bytes. 124 #define MEMORY_OFFSET_FILTER_AGE 15 // Age since filter installed in seconds. 125 126 // Leave 0 opcode unused as it's a good indicator of accidental incorrect execution (e.g. data). 127 #define LDB_OPCODE 1 // Load 1 byte from immediate offset, e.g. "ldb R0, [5]" 128 #define LDH_OPCODE 2 // Load 2 bytes from immediate offset, e.g. "ldh R0, [5]" 129 #define LDW_OPCODE 3 // Load 4 bytes from immediate offset, e.g. "ldw R0, [5]" 130 #define LDBX_OPCODE 4 // Load 1 byte from immediate offset plus register, e.g. "ldbx R0, [5]R0" 131 #define LDHX_OPCODE 5 // Load 2 byte from immediate offset plus register, e.g. "ldhx R0, [5]R0" 132 #define LDWX_OPCODE 6 // Load 4 byte from immediate offset plus register, e.g. "ldwx R0, [5]R0" 133 #define ADD_OPCODE 7 // Add, e.g. "add R0,5" 134 #define MUL_OPCODE 8 // Multiply, e.g. "mul R0,5" 135 #define DIV_OPCODE 9 // Divide, e.g. "div R0,5" 136 #define AND_OPCODE 10 // And, e.g. "and R0,5" 137 #define OR_OPCODE 11 // Or, e.g. "or R0,5" 138 #define SH_OPCODE 12 // Left shift, e.g, "sh R0, 5" or "sh R0, -5" (shifts right) 139 #define LI_OPCODE 13 // Load immediate, e.g. "li R0,5" (immediate encoded as signed value) 140 #define JMP_OPCODE 14 // Unconditional jump, e.g. "jmp label" 141 #define JEQ_OPCODE 15 // Compare equal and branch, e.g. "jeq R0,5,label" 142 #define JNE_OPCODE 16 // Compare not equal and branch, e.g. "jne R0,5,label" 143 #define JGT_OPCODE 17 // Compare greater than and branch, e.g. "jgt R0,5,label" 144 #define JLT_OPCODE 18 // Compare less than and branch, e.g. "jlt R0,5,label" 145 #define JSET_OPCODE 19 // Compare any bits set and branch, e.g. "jset R0,5,label" 146 #define JNEBS_OPCODE 20 // Compare not equal byte sequence, e.g. "jnebs R0,5,label,0x1122334455" 147 #define EXT_OPCODE 21 // Immediate value is one of *_EXT_OPCODE 148 // Extended opcodes. These all have an opcode of EXT_OPCODE 149 // and specify the actual opcode in the immediate field. 150 #define LDM_EXT_OPCODE 0 // Load from memory, e.g. "ldm R0,5" 151 // Values 0-15 represent loading the different memory slots. 152 #define STM_EXT_OPCODE 16 // Store to memory, e.g. "stm R0,5" 153 // Values 16-31 represent storing to the different memory slots. 154 #define NOT_EXT_OPCODE 32 // Not, e.g. "not R0" 155 #define NEG_EXT_OPCODE 33 // Negate, e.g. "neg R0" 156 #define SWAP_EXT_OPCODE 34 // Swap, e.g. "swap R0,R1" 157 #define MOV_EXT_OPCODE 35 // Move, e.g. "move R0,R1" 158 159 #define EXTRACT_OPCODE(i) (((i) >> 3) & 31) 160 #define EXTRACT_REGISTER(i) ((i) & 1) 161 #define EXTRACT_IMM_LENGTH(i) (((i) >> 1) & 3) 162
