Disable use of Linux memory protection keys #53
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
V8's default thread-isolated allocator has a bug on x64 Linux. It uses memory protection keys (see `man 7 pkeys`) to write-protect JIT code memory but in a way that is currently incompatible with how we use threads. Specifically, pkey permissions are inherited by child threads. Threads that are not descendants of the thread that allocates the pkey default to "no permissions" for that pkey. Concretely, if thread A creates the v8::Platform (and the pkey) and write-protects memory, then later thread B tries to access that memory, it segfaults due to the lack of permissions. The fix on V8's side is conceptually easy - call pkey_set(PKEY_DISABLE_WRITE) before accessing the memory, to flip the permissions from "none" to "can read" - but until it's actually fixed, disable thread-isolation. Fixes: rubyjs/mini_racer#300 Refs: https://issues.chromium.org/issues/360909072
|
Thanks Ben, I'll approve as soon as I get back in front of a computer!
|
SamSaffron
approved these changes
Aug 22, 2024
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
V8's default thread-isolated allocator has a bug on x64 Linux.
It uses memory protection keys (see
man 7 pkeys) to write-protect JIT code memory but in a way that is currently incompatible with how we use threads.Specifically, pkey permissions are inherited by child threads. Threads that are not descendants of the thread that allocates the pkey default to "no permissions" for that pkey.
Concretely, if thread A creates the v8::Platform (and the pkey) and write-protects memory, then later thread B tries to access that memory, it segfaults due to the lack of permissions.
The fix on V8's side is conceptually easy - call
pkey_set(PKEY_DISABLE_WRITE) before accessing the memory, to flip the permissions from "none" to "can read" - but until it's actually fixed, disable thread-isolation.
Fixes: rubyjs/mini_racer#300
Refs: https://issues.chromium.org/issues/360909072