benchmark: zero the ML-KEM key objects before the first wc_MlKemKey_Free

[dgarske]

bench_mlkem() passes its key objects to bench_mlkem_keygen(), which calls wc_MlKemKey_Free(key) at the top of its loop to release the previous iteration's key. On the first iteration there is no previous key and the object has only been allocated - with XMALLOC under WOLFSSL_SMALL_STACK, or left as an uninitialized stack array otherwise - so wc_MlKemKey_Free() disposes of whatever that memory happened to hold, calling XFREE on key->priv, key->pub and the PRF and hash objects. The same applies to key2, which reaches the trailing wc_MlKemKey_Free(key2) uninitialized when the encapsulate and decapsulate benchmarks are both compiled out. On a host allocator this usually goes unnoticed; on a bare-metal target it frees a wild pointer and faults. Zero both objects before use, which is what bench_frodokem() already does immediately above for the same reason.

Validated on an NXP i.MX95 Cortex-M7 running the benchmark under Zephyr, where the fault was reproducible, and with a host build of the benchmark.

[Copilot]

Copilot review overview

🟢 Approval recommended

The change is narrowly scoped, aligns with existing benchmark patterns (e.g., FrodoKEM), and directly prevents a confirmed invalid-free fault without introducing new control-flow or API behavior changes.

Review effort: Lite
Findings: None

What changed in this PR

This PR fixes a correctness issue in the ML-KEM benchmark where MlKemKey objects could be freed while still uninitialized (especially on the first iteration of bench_mlkem_keygen() and when encapsulate/decapsulate benchmarks are compiled out), which can trigger invalid frees on bare-metal/RTOS targets.

Changes:

• Zero-initialize key1 and key2 in bench_mlkem() before any benchmark helpers/free calls, ensuring wc_MlKemKey_Free() is safe even if a key was never initialized.

File	Description
wolfcrypt/​benchmark/​benchmark.c	Zeroes ML-KEM key objects before first free to prevent freeing garbage pointers in constrained/embedded environments.

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[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• gcc-arm-cortex-m0plus
• gcc-arm-cortex-m3
• gcc-arm-cortex-m4
• gcc-arm-cortex-m4-baremetal
• gcc-arm-cortex-m4-crypto-only
• gcc-arm-cortex-m4-dtls13
• gcc-arm-cortex-m4-min-ecc
• gcc-arm-cortex-m4-openssl-compat
• gcc-arm-cortex-m4-pkcs7
• gcc-arm-cortex-m4-pq
• gcc-arm-cortex-m4-rsa-only
• gcc-arm-cortex-m4-sp-math
• gcc-arm-cortex-m4-tls12
• gcc-arm-cortex-m4-tls13
• gcc-arm-cortex-m7
• gcc-arm-cortex-m7-pq
• gcc-arm-cortex-m7-tls13
• linuxkm-pie
• linuxkm-standard
• stm32-sim-stm32h753