chore(cli): build mimalloc in secure mode - #1356
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Moving off musl's mallocng lost a diagnostic property: mallocng validates
a check byte on every allocation, so heap corruption aborted the process
by itself. That is what produced the a_crash/enframe abort we used to
identify the intermittent lint segfault as heap corruption. A default
mimalloc build performs no equivalent check, so the same corruption would
now pass unnoticed and surface later as an unrelated failure.
Build mimalloc with its secure feature (MI_SECURE=4): guard pages around
metadata, encoded free lists, randomized placement, and double-free
detection. Verified the detectors are present in the musl release binary
("corrupted free list entry", "double free detected", "corrupted
meta-data in thread-free list").
Detection is silent unless mimalloc is told to report: show_errors and
abort_on_error are read from the environment at process start, so a run
that wants the diagnostic must be launched with MIMALLOC_SHOW_ERRORS=1
MIMALLOC_ABORT_ON_ERROR=1. Documented on the allocator item; setting them
from inside main does not work, as mimalloc reads its options before main
runs.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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mimalloc has no abort_on_error option — the earlier instruction to set MIMALLOC_ABORT_ON_ERROR was wrong and would have been silently ignored. mimalloc's default handler aborts only on EFAULT (corrupted metadata, corrupted thread-free list, and under the secure build a detected buffer overflow); a double free (EAGAIN) or a free of an invalid pointer (EINVAL) is reported and then execution continues. Register an error handler that aborts on every corruption code, so a detection is fatal at the point it happens rather than letting a corrupted heap run on and fail somewhere unrelated. The SIGABRT is caught by the crash handler, which reports it with a resolvable address. Adds a double-free trigger to the internal crash-test hook and an end-to-end test asserting the allocator reports it and the process dies by SIGABRT — the case that was previously silent. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Follow-up to #1355 (mimalloc). Builds mimalloc with its
securefeature and makes detected heap corruption fatal.Moving off musl's mallocng loses a diagnostic property we were relying on. mallocng validates a check byte on every allocation, so heap corruption aborted the process by itself — that is exactly what produced the
a_crash/enframeabort used to identify the intermittent lint segfault as heap corruption in the first place. A default mimalloc build performs no equivalent check, so the same corruption would now pass unnoticed and resurface later as an unrelated failure.Secure build.
MI_SECURE=4gives guard pages around metadata, encoded free lists, randomized placement, and double-free detection. Verified present in the builtx86_64-unknown-linux-muslrelease binary:corrupted free list entry of size %zub at %p,double free detected of block %p with size %zu, andcorrupted meta-data in thread-free list.Abort on detection. Detection alone is not enough: mimalloc's default handler aborts only on
EFAULT(corrupted metadata, corrupted thread-free list, and — undersecure— a detected buffer overflow), while a double free (EAGAIN) or a free of an invalid pointer (EINVAL) is reported and then execution continues. Continuing on a corrupted heap is what makes this class of bug so hard to trace: the eventual crash lands somewhere unrelated, long after the write that caused it. This registers an error handler viami_register_errorthat aborts on every corruption code, so a detection is fatal where it happens. The SIGABRT is caught by the crash handler, which reports it with a resolvable address.Setting
MIMALLOC_SHOW_ERRORS=1on a diagnostic run additionally prints the message saying what was detected (show_errorsdefaults off in a release build). The abort happens either way.Changes are visible to end-users: yes
Searched for relevant documentation and updated as needed: no (behavior is documented on the allocator item in
main.rs)Breaking change (forces users to change their own code or config): no
Suggested release notes appear below: yes
chore: the allocator is now built in secure mode and aborts when it detects heap corruption (a smashed free list, a double free, corrupted metadata) rather than continuing on a corrupted heap. Set
MIMALLOC_SHOW_ERRORS=1to also print what was detected.Test plan
double free detected) and the process dies by SIGABRT with a crash report — the path that was previously silent.x86_64-unknown-linux-muslrelease target builds via--config=release;mi_register_errorand all three secure detectors are linked into the binary, and it runs normally (aspect --version).Note on cost
MI_SECURE=4adds guard pages and free-list encoding, which is not free. If the perf hit is material we can land this as a diagnostic-only release and revert, the same way #1352 was scoped.