• Clemens Backes's avatar
    [wasm] Reset PKRU before spawning new threads · 8218c061
    Clemens Backes authored
    We sometimes hit the DCHECK in the wasm code manager:
      DCHECK_IMPLIES(writable, !MemoryProtectionKeyWritable());
    
    This is because we spawn new threads while having a
    {CodeSpaceWriteScope} open. In the case of PKU, this changes the PKRU
    register to allow writes to the code space, and the value of that
    register is inherited by any new thread. If this thread then tries to
    switch to writable code spaces, it hits the DCHECK. It would hit a
    similar DCHECK when trying to execute code.
    
    We fix this issue by temporarily resetting the PKRU register to
    non-writable while we call the {NotifyConcurrencyIncrease} method. This
    is not a very robust solution, as any new call that potentially happens
    inside a {CodeSpaceWriteScope} needs to do the same, but refactoring the
    code to avoid spawning new threads while being in writable state would
    be a lot of work with other downsides.
    
    R=jkummerow@chromium.org
    
    Bug: v8:13075
    Change-Id: Ibc7270aa597902dc6d9649cb6bcdfce8b1a9bafc
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3762579
    Commit-Queue: Clemens Backes <clemensb@chromium.org>
    Reviewed-by: 's avatarJakob Kummerow <jkummerow@chromium.org>
    Cr-Commit-Position: refs/heads/main@{#81729}
    8218c061
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