Merge 216da0b7 (automated)

1 files changed, 129 insertions, 0 deletions

diff --git a/pkg/bpf/bpf.go b/pkg/bpf/bpf.go
new file mode 100644
index 000000000..eb546f48f
--- /dev/null
+++ b/pkg/bpf/bpf.go
@@ -0,0 +1,129 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package bpf provides tools for working with Berkeley Packet Filter (BPF)
+// programs. More information on BPF can be found at
+// https://www.freebsd.org/cgi/man.cgi?bpf(4)
+package bpf
+
+import "gvisor.googlesource.com/gvisor/pkg/abi/linux"
+
+const (
+	// MaxInstructions is the maximum number of instructions in a BPF program,
+	// and is equal to Linux's BPF_MAXINSNS.
+	MaxInstructions = 4096
+
+	// ScratchMemRegisters is the number of M registers in a BPF virtual machine,
+	// and is equal to Linux's BPF_MEMWORDS.
+	ScratchMemRegisters = 16
+)
+
+// Parts of a linux.BPFInstruction.OpCode. Compare to the Linux kernel's
+// include/uapi/linux/filter.h.
+//
+// In the comments below:
+//
+// - A, X, and M[] are BPF virtual machine registers.
+//
+// - K refers to the instruction field linux.BPFInstruction.K.
+//
+// - Bits are counted from the LSB position.
+const (
+	// Instruction class, stored in bits 0-2.
+	Ld                   = 0x00 // load into A
+	Ldx                  = 0x01 // load into X
+	St                   = 0x02 // store from A
+	Stx                  = 0x03 // store from X
+	Alu                  = 0x04 // arithmetic
+	Jmp                  = 0x05 // jump
+	Ret                  = 0x06 // return
+	Misc                 = 0x07
+	instructionClassMask = 0x07
+
+	// Size of a load, stored in bits 3-4.
+	W            = 0x00 // 32 bits
+	H            = 0x08 // 16 bits
+	B            = 0x10 // 8 bits
+	loadSizeMask = 0x18
+
+	// Source operand for a load, stored in bits 5-7.
+	// Address mode numbers in the comments come from Linux's
+	// Documentation/networking/filter.txt.
+	Imm          = 0x00 // immediate value K (mode 4)
+	Abs          = 0x20 // data in input at byte offset K (mode 1)
+	Ind          = 0x40 // data in input at byte offset X+K (mode 2)
+	Mem          = 0x60 // M[K] (mode 3)
+	Len          = 0x80 // length of the input in bytes ("BPF extension len")
+	Msh          = 0xa0 // 4 * lower nibble of input at byte offset K (mode 5)
+	loadModeMask = 0xe0
+
+	// Source operands for arithmetic, jump, and return instructions.
+	// Arithmetic and jump instructions can use K or X as source operands.
+	// Return instructions can use K or A as source operands.
+	K             = 0x00 // still mode 4
+	X             = 0x08 // mode 0
+	A             = 0x10 // mode 9
+	srcAluJmpMask = 0x08
+	srcRetMask    = 0x18
+
+	// Arithmetic instructions, stored in bits 4-7.
+	Add     = 0x00
+	Sub     = 0x10 // A - src
+	Mul     = 0x20
+	Div     = 0x30 // A / src
+	Or      = 0x40
+	And     = 0x50
+	Lsh     = 0x60 // A << src
+	Rsh     = 0x70 // A >> src
+	Neg     = 0x80 // -A (src ignored)
+	Mod     = 0x90 // A % src
+	Xor     = 0xa0
+	aluMask = 0xf0
+
+	// Jump instructions, stored in bits 4-7.
+	Ja      = 0x00 // unconditional (uses K for jump offset)
+	Jeq     = 0x10 // if A == src
+	Jgt     = 0x20 // if A > src
+	Jge     = 0x30 // if A >= src
+	Jset    = 0x40 // if (A & src) != 0
+	jmpMask = 0xf0
+
+	// Miscellaneous instructions, stored in bits 3-7.
+	Tax      = 0x00 // A = X
+	Txa      = 0x80 // X = A
+	miscMask = 0xf8
+
+	// Masks for bits that should be zero.
+	unusedBitsMask      = 0xff00 // all valid instructions use only bits 0-7
+	storeUnusedBitsMask = 0xf8   // stores only use instruction class
+	retUnusedBitsMask   = 0xe0   // returns only use instruction class and source operand
+)
+
+// Stmt returns a linux.BPFInstruction representing a BPF non-jump instruction.
+func Stmt(code uint16, k uint32) linux.BPFInstruction {
+	return linux.BPFInstruction{
+		OpCode: code,
+		K:      k,
+	}
+}
+
+// Jump returns a linux.BPFInstruction representing a BPF jump instruction.
+func Jump(code uint16, k uint32, jt, jf uint8) linux.BPFInstruction {
+	return linux.BPFInstruction{
+		OpCode:      code,
+		JumpIfTrue:  jt,
+		JumpIfFalse: jf,
+		K:           k,
+	}
+}