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Fix memory leaks in WASI setjmp handler #12995

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Merged
merged 3 commits into from
Mar 31, 2025
Merged

Fix memory leaks in WASI setjmp handler #12995

merged 3 commits into from
Mar 31, 2025

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white-axe
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This pull request fixes two memory leaks in the implementation of setjmp in WASI (WebAssembly) builds of Ruby:

  • The first commit fixes a problem where the stack pointer is not reset after a longjmp, leading to leaking of parts of the stack. This also causes leaking of Ruby objects since the garbage collector looks for GC roots on the stack.
  • The second commit fixes a problem where the VM jump buffers are not freed after a longjmp. In WASI builds of Ruby, jump buffers are allocated on the heap instead of on the stack, so they need to be manually deallocated. I changed the implementations of rb_vm_tag_jmpbuf_init() and rb_vm_tag_jmpbuf_deinit() to clean up leaked jump buffers before initializing/deinitializing jump buffers.

@white-axe white-axe marked this pull request as draft March 27, 2025 05:20
@white-axe white-axe marked this pull request as ready for review March 27, 2025 06:05
@white-axe
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@kateinoigakukun, since you maintain the WASI builds of Ruby, can you take a look at this?

@kateinoigakukun
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Let me execute ruby.wasm test suite with this change: ruby/ruby.wasm#586

@white-axe
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Here's a test to see if a WASI build is affected by these two memory leaks. This script causes all of the current WASI builds from https://github.com/ruby/ruby.wasm to rapidly consume around 800 mebibytes of memory due to the jump buffer leak and then crash from what I believe is stack buffer overflow caused by the stack pointer leak:

loop do
  array = [0]
  for item in array
    break
  end
end

To test it out, save it as test.rb in the current working directory, and then:

curl -Lo ruby.tar.gz https://github.com/ruby/ruby.wasm/releases/download/2.7.1/ruby-3.4-wasm32-unknown-wasip1-full.tar.gz
tar xzf ruby.tar.gz --strip-components=1
wasmtime --dir .::/ usr/local/bin/ruby test.rb

kateinoigakukun
kateinoigakukun approved these changes Mar 31, 2025
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Really good catch, the patch looks good to me.

@kateinoigakukun kateinoigakukun merged commit 372515f into ruby:master Mar 31, 2025
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@white-axe white-axe deleted the wasi-leak branch March 31, 2025 15:54
white-axe added a commit to white-axe/mkxp-z that referenced this pull request Mar 31, 2025
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Apply patch from ruby/ruby#12995 in libretro builds
12f12d9
@kateinoigakukun
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kateinoigakukun commented Apr 1, 2025 •
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Hi @white-axe, the change seems causing OOM on ruby.wasm test suite, so I'm reverting this for now #13026

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I'll find some other way to fix the second memory leak then

@white-axe white-axe mentioned this pull request Apr 3, 2025
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@white-axe white-axe mentioned this pull request Apr 20, 2025
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@kateinoigakukun kateinoigakukun kateinoigakukun approved these changes

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