Creates BA3011 check for presence of BIND_NOW flag AKA full RELRO #363
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,111 @@ | ||
| // Copyright (c) Microsoft. All rights reserved. | ||
| // Licensed under the MIT license. See LICENSE file in the project root for full license information. | ||
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| using System; | ||
| using System.Collections.Generic; | ||
| using System.Composition; | ||
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| using ELFSharp.ELF; | ||
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| using Microsoft.CodeAnalysis.BinaryParsers; | ||
| using Microsoft.CodeAnalysis.IL.Sdk; | ||
| using Microsoft.CodeAnalysis.Sarif; | ||
| using Microsoft.CodeAnalysis.Sarif.Driver; | ||
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| namespace Microsoft.CodeAnalysis.IL.Rules | ||
| { | ||
| [Export(typeof(Skimmer<BinaryAnalyzerContext>)), Export(typeof(ReportingDescriptor))] | ||
| public class EnableBindNow : ELFBinarySkimmerBase | ||
| { | ||
| private const uint DF_1_NOW = 0x1; | ||
| private const uint DF_BIND_NOW = 0x8; | ||
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| /// <summary> | ||
| /// BA3011 | ||
| /// </summary> | ||
| public override string Id => RuleIds.EnableBindNow; | ||
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| /// <summary> | ||
| /// This check ensures that some relocation data is marked as read only after | ||
| /// the executable is loaded, and moved below the .data section in memory. | ||
| /// This prevents them from being overwritten, which can redirect control flow. | ||
| /// Use the compiler flags '-Wl,z,now' to enable this. | ||
| /// </summary> | ||
| public override MultiformatMessageString FullDescription => new MultiformatMessageString { Text = RuleResources.BA3011_EnableBindNow_Description }; | ||
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| protected override IEnumerable<string> MessageResourceNames => new string[] { | ||
| nameof(RuleResources.BA3011_Pass), | ||
| nameof(RuleResources.BA3011_Error), | ||
| nameof(RuleResources.NotApplicable_InvalidMetadata) | ||
| }; | ||
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| public override AnalysisApplicability CanAnalyzeElf(ELFBinary target, Sarif.PropertiesDictionary policy, out string reasonForNotAnalyzing) | ||
| { | ||
| IELF elf = target.ELF; | ||
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| if (elf.Type == FileType.Core || elf.Type == FileType.None || elf.Type == FileType.Relocatable) | ||
| { | ||
| reasonForNotAnalyzing = MetadataConditions.ElfIsCoreNoneOrObject; | ||
| return AnalysisApplicability.NotApplicableToSpecifiedTarget; | ||
| } | ||
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| reasonForNotAnalyzing = null; | ||
| return AnalysisApplicability.ApplicableToSpecifiedTarget; | ||
| } | ||
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| public override void Analyze(BinaryAnalyzerContext context) | ||
| { | ||
| IELF elf = context.ELFBinary().ELF; | ||
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| if (HasBindNowFlag(elf)) | ||
| { | ||
| // Pass | ||
| context.Logger.Log(this, | ||
| RuleUtilities.BuildResult(ResultKind.Pass, context, null, | ||
| nameof(RuleResources.BA3011_Pass), | ||
| context.TargetUri.GetFileName())); | ||
| } | ||
| else | ||
| { | ||
| // Fail | ||
| context.Logger.Log(this, | ||
| RuleUtilities.BuildResult(FailureLevel.Error, context, null, | ||
| nameof(RuleResources.BA3011_Error), | ||
| context.TargetUri.GetFileName())); | ||
| } | ||
| } | ||
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| // Pwntools checksec calls out numerous ways an ELF can specify full RELRO to the | ||
| // loader. All have the intended effect of eagerly resolving all plt functions and | ||
| // subsequently marking the entire GOT read-only (at least, when there | ||
| // is also a GNU_RELRO section) | ||
| // https://github.com/Gallopsled/pwntools/blob/ec9dfe108b85ac47983e9a98808fcdbb50cb0cdd/pwnlib/elf/elf.py#L1578 | ||
| private static bool HasBindNowFlag(IELF elf) | ||
| { | ||
| try | ||
| { | ||
| var dynamicSection = (ELFSharp.ELF.Sections.IDynamicSection)elf.GetSection(".dynamic"); | ||
| if (dynamicSection == null) | ||
| { | ||
| return false; | ||
| } | ||
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| foreach (ELFSharp.ELF.Sections.DynamicEntry<ulong> entry in dynamicSection.Entries) | ||
| { | ||
| if ((entry.Tag == ELFSharp.ELF.Sections.DynamicTag.BindNow) || | ||
| (entry.Tag == ELFSharp.ELF.Sections.DynamicTag.Flags && (entry.Value & DF_BIND_NOW) != 0) || | ||
| (entry.Tag == ELFSharp.ELF.Sections.DynamicTag.Flags1 && (entry.Value & DF_1_NOW) != 0)) | ||
| { | ||
| return true; | ||
| } | ||
| } | ||
| } | ||
| catch (InvalidCastException) | ||
| { | ||
| return false; | ||
| } | ||
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| return false; | ||
| } | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -48,8 +48,8 @@ internal static class RuleIds | |
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| // Skipping some check namespace (BA3004-3009) for future checks | ||
| public const string EnableReadOnlyRelocations = "BA3010"; | ||
| public const string EnableBindNow = "BA3011"; | ||
|
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Good names! Let's add test cases for this rule, @eddynaka. #Closed There was a problem hiding this comment. FYI there are some test cases for this already: Spoke offline with Eddy, and it may be helpful to update the no_immediate_binding test to explicitly use RTLD_LAZY binding: |
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| // BA3012-3029 -- saved for future non-compiler/language specific checks. | ||
| // Compiler/Language specific checks follow. | ||
| public const string UseCheckedFunctionsWithGcc = "BA3030"; | ||
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Just curious, what's producing these exceptions? #Closed
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The project I'm working on separates executables into two files like in this post. The .dbg file contains only debug info, and therefore isn't even executable. But since it's an ELF, it gets parsed by
binskim analyze. Since the file contains no executable code, the output of binskim is meaningless, so I was happy to just silence the exception.I haven't seen any other case where this happens. #Closed