126 lines
3.4 KiB
Go
126 lines
3.4 KiB
Go
// Copyright 2017-2018 DigitalOcean.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package smbios
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import (
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"bytes"
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"errors"
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"io"
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"io/ioutil"
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"os"
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)
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const (
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// devMem is the UNIX-like system memory device location used to
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// find SMBIOS information.
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devMem = "/dev/mem"
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// SMBIOS specification indicates that the entry point should exist
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// between these two memory addresses.
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startAddr = 0x000f0000
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endAddr = 0x000fffff
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)
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// memoryStream reads the SMBIOS entry point and structure stream from
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// an io.ReadSeeker (usually system memory).
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//
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// memoryStream is an entry point for tests.
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func memoryStream(rs io.ReadSeeker, startAddr, endAddr int) (io.ReadCloser, EntryPoint, error) {
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// Try to find the entry point.
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addr, err := findEntryPoint(rs, startAddr, endAddr)
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if err != nil {
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return nil, nil, err
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}
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// Found it; seek to the location of the entry point.
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if _, err := rs.Seek(int64(addr), io.SeekStart); err != nil {
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return nil, nil, err
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}
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// Read the entry point and determine where the SMBIOS table is.
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ep, err := ParseEntryPoint(rs)
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if err != nil {
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return nil, nil, err
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}
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// Seek to the start of the SMBIOS table.
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tableAddr, tableSize := ep.Table()
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if _, err := rs.Seek(int64(tableAddr), io.SeekStart); err != nil {
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return nil, nil, err
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}
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// Make a copy of the memory so we don't return a handle to system memory
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// to the caller.
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out := make([]byte, tableSize)
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if _, err := io.ReadFull(rs, out); err != nil {
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return nil, nil, err
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}
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return ioutil.NopCloser(bytes.NewReader(out)), ep, nil
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}
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// findEntryPoint attempts to locate the entry point structure in the io.ReadSeeker
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// using the start and end bound as hints for its location.
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func findEntryPoint(rs io.ReadSeeker, start, end int) (int, error) {
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// Begin searching at the start bound.
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if _, err := rs.Seek(int64(start), io.SeekStart); err != nil {
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return 0, err
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}
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// Iterate one "paragraph" of memory at a time until we either find the entry point
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// or reach the end bound.
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const paragraph = 16
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b := make([]byte, paragraph)
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var (
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addr int
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found bool
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)
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for addr = start; addr < end; addr += paragraph {
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if _, err := io.ReadFull(rs, b); err != nil {
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return 0, err
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}
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// Both the 32-bit and 64-bit entry point have a similar prefix.
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if bytes.HasPrefix(b, magicPrefix) {
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found = true
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break
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}
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}
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if !found {
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return 0, errors.New("no SMBIOS entry point found in memory")
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}
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// Return the exact memory location of the entry point.
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return addr, nil
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}
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// devMemStream reads the SMBIOS entry point and structure stream from
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// the UNIX-like system /dev/mem device.
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//
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// This is UNIX-like system specific, but since it doesn't employ any system
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// calls or OS-dependent constants, it remains in this file for simplicity.
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func devMemStream() (io.ReadCloser, EntryPoint, error) {
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mem, err := os.Open(devMem)
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if err != nil {
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return nil, nil, err
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}
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defer mem.Close()
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return memoryStream(mem, startAddr, endAddr)
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}
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