[Webkit-unassigned] [Bug 209632] New: Clear the entropy bits in the encodedStructureBits when deallocating a structureID.

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Mar 26 17:14:20 PDT 2020


https://bugs.webkit.org/show_bug.cgi?id=209632

            Bug ID: 209632
           Summary: Clear the entropy bits in the encodedStructureBits
                    when deallocating a structureID.
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mark.lam at apple.com

We currently only use a 32-bit offset in the StructureIDTable's StructureOrOffset.  Though we will never store an offset value that is near 32-bit in size, let alone 64-bit, there's no reason why we can't just use all 64-bits for the offset.  Doing so will also have the benefit of zero'ing out the entropy bits in the old encodedStructureBits.  This guarantees there's no chance of coalition between a "freed" structureID's entropy bits and the entropy bits in a dead cell due to GC bugs.

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