Exclude guard page from stack bounds check in initialize#13704
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cfallin merged 1 commit intoJun 22, 2026
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Fix the bounds check in VMContinuationStack::initialize to compare against usable stack space rather than total allocation size. Prior to bytecodealliance#13662, initialize() had no bounds check at all, so a high-arity function type (e.g. 600 params on an 8192-byte stack) would unconditionally write control data into the guard page and segfault. PR bytecodealliance#13662 added a bounds check, but compared against self.len which for Mmap allocations includes the guard page. This meant the 600-param case still slipped through: 9664 <= 12288 passed the check, but the write still landed in the non-writable guard page. This fix subtracts the guard page size for Mmap allocations so the check reflects the actual usable stack space. Custom allocations are unaffected since their len does not include a guard page. Adds a regression test matching the exact scenario from bytecodealliance#13703 (600 params on an 8192-byte stack). Closes bytecodealliance#13703 Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>
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Fix the bounds check in
VMContinuationStack::initializeto compareagainst usable stack space rather than total allocation size.
Prior to #13662,
initialize()had no bounds check at all, so ahigh-arity function type (e.g. 600 params on an 8192-byte stack)
would unconditionally write control data into the guard page and
segfault. PR #13662 added a bounds check, but compared against
self.lenwhich for Mmap allocations includes the guard page. Thismeant the 600-param case still slipped through:
9664 <= 12288passed the check, but the write still landed in the non-writable
guard page.
This fix subtracts the guard page size for Mmap allocations so
the check reflects the actual usable stack space. Custom
allocations are unaffected since their
lendoes not include aguard page.
Adds a regression test matching the exact scenario from #13703
(600 params on an 8192-byte stack).
Closes #13703