security.go

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Checking of compiler and linker flags.
     6  // We must avoid flags like -fplugin=, which can allow
     7  // arbitrary code execution during the build.
     8  // Do not make changes here without carefully
     9  // considering the implications.
    10  // (That's why the code is isolated in a file named security.go.)
    11  //
    12  // Note that -Wl,foo means split foo on commas and pass to
    13  // the linker, so that -Wl,-foo,bar means pass -foo bar to
    14  // the linker. Similarly -Wa,foo for the assembler and so on.
    15  // If any of these are permitted, the wildcard portion must
    16  // disallow commas.
    17  //
    18  // Note also that GNU binutils accept any argument @foo
    19  // as meaning "read more flags from the file foo", so we must
    20  // guard against any command-line argument beginning with @,
    21  // even things like "-I @foo".
    22  // We use load.SafeArg (which is even more conservative)
    23  // to reject these.
    24  //
    25  // Even worse, gcc -I@foo (one arg) turns into cc1 -I @foo (two args),
    26  // so although gcc doesn't expand the @foo, cc1 will.
    27  // So out of paranoia, we reject @ at the beginning of every
    28  // flag argument that might be split into its own argument.
    29  
    30  package work
    31  
    32  import (
    33  	"fmt"
    34  	"internal/lazyregexp"
    35  	"regexp"
    36  	"strings"
    37  
    38  	"cmd/go/internal/cfg"
    39  	"cmd/go/internal/load"
    40  )
    41  
    42  var re = lazyregexp.New
    43  
    44  var validCompilerFlags = []*lazyregexp.Regexp{
    45  	re(`-D([A-Za-z_][A-Za-z0-9_]*)(=[^@\-]*)?`),
    46  	re(`-U([A-Za-z_][A-Za-z0-9_]*)`),
    47  	re(`-F([^@\-].*)`),
    48  	re(`-I([^@\-].*)`),
    49  	re(`-O`),
    50  	re(`-O([^@\-].*)`),
    51  	re(`-W`),
    52  	re(`-W([^@,]+)`), // -Wall but not -Wa,-foo.
    53  	re(`-Wa,-mbig-obj`),
    54  	re(`-Wp,-D([A-Za-z_][A-Za-z0-9_]*)(=[^@,\-]*)?`),
    55  	re(`-Wp,-U([A-Za-z_][A-Za-z0-9_]*)`),
    56  	re(`-ansi`),
    57  	re(`-f(no-)?asynchronous-unwind-tables`),
    58  	re(`-f(no-)?blocks`),
    59  	re(`-f(no-)builtin-[a-zA-Z0-9_]*`),
    60  	re(`-f(no-)?common`),
    61  	re(`-f(no-)?constant-cfstrings`),
    62  	re(`-fdebug-prefix-map=([^@]+)=([^@]+)`),
    63  	re(`-fdiagnostics-show-note-include-stack`),
    64  	re(`-ffile-prefix-map=([^@]+)=([^@]+)`),
    65  	re(`-fno-canonical-system-headers`),
    66  	re(`-f(no-)?eliminate-unused-debug-types`),
    67  	re(`-f(no-)?exceptions`),
    68  	re(`-f(no-)?fast-math`),
    69  	re(`-f(no-)?inline-functions`),
    70  	re(`-finput-charset=([^@\-].*)`),
    71  	re(`-f(no-)?fat-lto-objects`),
    72  	re(`-f(no-)?keep-inline-dllexport`),
    73  	re(`-f(no-)?lto`),
    74  	re(`-fmacro-backtrace-limit=(.+)`),
    75  	re(`-fmessage-length=(.+)`),
    76  	re(`-f(no-)?modules`),
    77  	re(`-f(no-)?objc-arc`),
    78  	re(`-f(no-)?objc-nonfragile-abi`),
    79  	re(`-f(no-)?objc-legacy-dispatch`),
    80  	re(`-f(no-)?omit-frame-pointer`),
    81  	re(`-f(no-)?openmp(-simd)?`),
    82  	re(`-f(no-)?permissive`),
    83  	re(`-f(no-)?(pic|PIC|pie|PIE)`),
    84  	re(`-f(no-)?plt`),
    85  	re(`-f(no-)?rtti`),
    86  	re(`-f(no-)?split-stack`),
    87  	re(`-f(no-)?stack-(.+)`),
    88  	re(`-f(no-)?strict-aliasing`),
    89  	re(`-f(un)signed-char`),
    90  	re(`-f(no-)?use-linker-plugin`), // safe if -B is not used; we don't permit -B
    91  	re(`-f(no-)?visibility-inlines-hidden`),
    92  	re(`-fsanitize=(.+)`),
    93  	re(`-ftemplate-depth-(.+)`),
    94  	re(`-fvisibility=(.+)`),
    95  	re(`-g([^@\-].*)?`),
    96  	re(`-m32`),
    97  	re(`-m64`),
    98  	re(`-m(abi|arch|cpu|fpu|tune)=([^@\-].*)`),
    99  	re(`-m(no-)?v?aes`),
   100  	re(`-marm`),
   101  	re(`-m(no-)?avx[0-9a-z]*`),
   102  	re(`-mcmodel=[0-9a-z-]+`),
   103  	re(`-mfloat-abi=([^@\-].*)`),
   104  	re(`-mfpmath=[0-9a-z,+]*`),
   105  	re(`-m(no-)?avx[0-9a-z.]*`),
   106  	re(`-m(no-)?ms-bitfields`),
   107  	re(`-m(no-)?stack-(.+)`),
   108  	re(`-mmacosx-(.+)`),
   109  	re(`-mios-simulator-version-min=(.+)`),
   110  	re(`-miphoneos-version-min=(.+)`),
   111  	re(`-mlarge-data-threshold=[0-9]+`),
   112  	re(`-mtvos-simulator-version-min=(.+)`),
   113  	re(`-mtvos-version-min=(.+)`),
   114  	re(`-mwatchos-simulator-version-min=(.+)`),
   115  	re(`-mwatchos-version-min=(.+)`),
   116  	re(`-mnop-fun-dllimport`),
   117  	re(`-m(no-)?sse[0-9.]*`),
   118  	re(`-m(no-)?ssse3`),
   119  	re(`-mthumb(-interwork)?`),
   120  	re(`-mthreads`),
   121  	re(`-mwindows`),
   122  	re(`-no-canonical-prefixes`),
   123  	re(`--param=ssp-buffer-size=[0-9]*`),
   124  	re(`-pedantic(-errors)?`),
   125  	re(`-pipe`),
   126  	re(`-pthread`),
   127  	re(`-?-std=([^@\-].*)`),
   128  	re(`-?-stdlib=([^@\-].*)`),
   129  	re(`--sysroot=([^@\-].*)`),
   130  	re(`-w`),
   131  	re(`-x([^@\-].*)`),
   132  	re(`-v`),
   133  }
   134  
   135  var validCompilerFlagsWithNextArg = []string{
   136  	"-arch",
   137  	"-D",
   138  	"-U",
   139  	"-I",
   140  	"-F",
   141  	"-framework",
   142  	"-include",
   143  	"-isysroot",
   144  	"-isystem",
   145  	"--sysroot",
   146  	"-target",
   147  	"-x",
   148  }
   149  
   150  var invalidLinkerFlags = []*lazyregexp.Regexp{
   151  	// On macOS this means the linker loads and executes the next argument.
   152  	// Have to exclude separately because -lfoo is allowed in general.
   153  	re(`-lto_library`),
   154  }
   155  
   156  var validLinkerFlags = []*lazyregexp.Regexp{
   157  	re(`-F([^@\-].*)`),
   158  	re(`-l([^@\-].*)`),
   159  	re(`-L([^@\-].*)`),
   160  	re(`-O`),
   161  	re(`-O([^@\-].*)`),
   162  	re(`-f(no-)?(pic|PIC|pie|PIE)`),
   163  	re(`-f(no-)?openmp(-simd)?`),
   164  	re(`-fsanitize=([^@\-].*)`),
   165  	re(`-flat_namespace`),
   166  	re(`-g([^@\-].*)?`),
   167  	re(`-headerpad_max_install_names`),
   168  	re(`-m(abi|arch|cpu|fpu|tune)=([^@\-].*)`),
   169  	re(`-mfloat-abi=([^@\-].*)`),
   170  	re(`-mmacosx-(.+)`),
   171  	re(`-mios-simulator-version-min=(.+)`),
   172  	re(`-miphoneos-version-min=(.+)`),
   173  	re(`-mthreads`),
   174  	re(`-mwindows`),
   175  	re(`-(pic|PIC|pie|PIE)`),
   176  	re(`-pthread`),
   177  	re(`-rdynamic`),
   178  	re(`-shared`),
   179  	re(`-?-static([-a-z0-9+]*)`),
   180  	re(`-?-stdlib=([^@\-].*)`),
   181  	re(`-v`),
   182  
   183  	// Note that any wildcards in -Wl need to exclude comma,
   184  	// since -Wl splits its argument at commas and passes
   185  	// them all to the linker uninterpreted. Allowing comma
   186  	// in a wildcard would allow tunneling arbitrary additional
   187  	// linker arguments through one of these.
   188  	re(`-Wl,--(no-)?allow-multiple-definition`),
   189  	re(`-Wl,--(no-)?allow-shlib-undefined`),
   190  	re(`-Wl,--(no-)?as-needed`),
   191  	re(`-Wl,-Bdynamic`),
   192  	re(`-Wl,-berok`),
   193  	re(`-Wl,-Bstatic`),
   194  	re(`-Wl,-Bsymbolic-functions`),
   195  	re(`-Wl,-O[0-9]+`),
   196  	re(`-Wl,-d[ny]`),
   197  	re(`-Wl,--disable-new-dtags`),
   198  	re(`-Wl,-e[=,][a-zA-Z0-9]+`),
   199  	re(`-Wl,--enable-new-dtags`),
   200  	re(`-Wl,--end-group`),
   201  	re(`-Wl,--(no-)?export-dynamic`),
   202  	re(`-Wl,-E`),
   203  	re(`-Wl,-framework,[^,@\-][^,]+`),
   204  	re(`-Wl,--hash-style=(sysv|gnu|both)`),
   205  	re(`-Wl,-headerpad_max_install_names`),
   206  	re(`-Wl,--no-undefined`),
   207  	re(`-Wl,-R,?([^@\-,][^,@]*$)`),
   208  	re(`-Wl,--just-symbols[=,]([^,@\-][^,@]+)`),
   209  	re(`-Wl,-rpath(-link)?[=,]([^,@\-][^,]+)`),
   210  	re(`-Wl,-s`),
   211  	re(`-Wl,-search_paths_first`),
   212  	re(`-Wl,-sectcreate,([^,@\-][^,]+),([^,@\-][^,]+),([^,@\-][^,]+)`),
   213  	re(`-Wl,--start-group`),
   214  	re(`-Wl,-?-static`),
   215  	re(`-Wl,-?-subsystem,(native|windows|console|posix|xbox)`),
   216  	re(`-Wl,-syslibroot[=,]([^,@\-][^,]+)`),
   217  	re(`-Wl,-undefined[=,]([^,@\-][^,]+)`),
   218  	re(`-Wl,-?-unresolved-symbols=[^,]+`),
   219  	re(`-Wl,--(no-)?warn-([^,]+)`),
   220  	re(`-Wl,-?-wrap[=,][^,@\-][^,]*`),
   221  	re(`-Wl(,-z,(relro|now|(no)?execstack))+`),
   222  
   223  	re(`[a-zA-Z0-9_/].*\.(a|o|obj|dll|dylib|so|tbd)`), // direct linker inputs: x.o or libfoo.so (but not -foo.o or @foo.o)
   224  	re(`\./.*\.(a|o|obj|dll|dylib|so|tbd)`),
   225  }
   226  
   227  var validLinkerFlagsWithNextArg = []string{
   228  	"-arch",
   229  	"-F",
   230  	"-l",
   231  	"-L",
   232  	"-framework",
   233  	"-isysroot",
   234  	"--sysroot",
   235  	"-target",
   236  	"-Wl,-framework",
   237  	"-Wl,-rpath",
   238  	"-Wl,-R",
   239  	"-Wl,--just-symbols",
   240  	"-Wl,-undefined",
   241  }
   242  
   243  func checkCompilerFlags(name, source string, list []string) error {
   244  	checkOverrides := true
   245  	return checkFlags(name, source, list, nil, validCompilerFlags, validCompilerFlagsWithNextArg, checkOverrides)
   246  }
   247  
   248  func checkLinkerFlags(name, source string, list []string) error {
   249  	checkOverrides := true
   250  	return checkFlags(name, source, list, invalidLinkerFlags, validLinkerFlags, validLinkerFlagsWithNextArg, checkOverrides)
   251  }
   252  
   253  // checkCompilerFlagsForInternalLink returns an error if 'list'
   254  // contains a flag or flags that may not be fully supported by
   255  // internal linking (meaning that we should punt the link to the
   256  // external linker).
   257  func checkCompilerFlagsForInternalLink(name, source string, list []string) error {
   258  	checkOverrides := false
   259  	if err := checkFlags(name, source, list, nil, validCompilerFlags, validCompilerFlagsWithNextArg, checkOverrides); err != nil {
   260  		return err
   261  	}
   262  	// Currently the only flag on the allow list that causes problems
   263  	// for the linker is "-flto"; check for it manually here.
   264  	for _, fl := range list {
   265  		if strings.HasPrefix(fl, "-flto") {
   266  			return fmt.Errorf("flag %q triggers external linking", fl)
   267  		}
   268  	}
   269  	return nil
   270  }
   271  
   272  func checkFlags(name, source string, list []string, invalid, valid []*lazyregexp.Regexp, validNext []string, checkOverrides bool) error {
   273  	// Let users override rules with $CGO_CFLAGS_ALLOW, $CGO_CFLAGS_DISALLOW, etc.
   274  	var (
   275  		allow    *regexp.Regexp
   276  		disallow *regexp.Regexp
   277  	)
   278  	if checkOverrides {
   279  		if env := cfg.Getenv("CGO_" + name + "_ALLOW"); env != "" {
   280  			r, err := regexp.Compile(env)
   281  			if err != nil {
   282  				return fmt.Errorf("parsing $CGO_%s_ALLOW: %v", name, err)
   283  			}
   284  			allow = r
   285  		}
   286  		if env := cfg.Getenv("CGO_" + name + "_DISALLOW"); env != "" {
   287  			r, err := regexp.Compile(env)
   288  			if err != nil {
   289  				return fmt.Errorf("parsing $CGO_%s_DISALLOW: %v", name, err)
   290  			}
   291  			disallow = r
   292  		}
   293  	}
   294  
   295  Args:
   296  	for i := 0; i < len(list); i++ {
   297  		arg := list[i]
   298  		if disallow != nil && disallow.FindString(arg) == arg {
   299  			goto Bad
   300  		}
   301  		if allow != nil && allow.FindString(arg) == arg {
   302  			continue Args
   303  		}
   304  		for _, re := range invalid {
   305  			if re.FindString(arg) == arg { // must be complete match
   306  				goto Bad
   307  			}
   308  		}
   309  		for _, re := range valid {
   310  			if re.FindString(arg) == arg { // must be complete match
   311  				continue Args
   312  			}
   313  		}
   314  		for _, x := range validNext {
   315  			if arg == x {
   316  				if i+1 < len(list) && load.SafeArg(list[i+1]) {
   317  					i++
   318  					continue Args
   319  				}
   320  
   321  				// Permit -Wl,-framework -Wl,name.
   322  				if i+1 < len(list) &&
   323  					strings.HasPrefix(arg, "-Wl,") &&
   324  					strings.HasPrefix(list[i+1], "-Wl,") &&
   325  					load.SafeArg(list[i+1][4:]) &&
   326  					!strings.Contains(list[i+1][4:], ",") {
   327  					i++
   328  					continue Args
   329  				}
   330  
   331  				// Permit -I= /path, -I $SYSROOT.
   332  				if i+1 < len(list) && arg == "-I" {
   333  					if (strings.HasPrefix(list[i+1], "=") || strings.HasPrefix(list[i+1], "$SYSROOT")) &&
   334  						load.SafeArg(list[i+1][1:]) {
   335  						i++
   336  						continue Args
   337  					}
   338  				}
   339  
   340  				if i+1 < len(list) {
   341  					return fmt.Errorf("invalid flag in %s: %s %s (see https://golang.org/s/invalidflag)", source, arg, list[i+1])
   342  				}
   343  				return fmt.Errorf("invalid flag in %s: %s without argument (see https://golang.org/s/invalidflag)", source, arg)
   344  			}
   345  		}
   346  	Bad:
   347  		return fmt.Errorf("invalid flag in %s: %s", source, arg)
   348  	}
   349  	return nil
   350  }
   351
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