CVE-2024-26712

What it actually does

The flaw in kasan_init_region performs incorrect page masking on a non-aligned k_start, causing va = block + k_cur - k_start to compute an address before the memblock-allocated block and write outside the reserved region.

Why it matters to the business

PowerPC Linux systems using KASAN may suffer memory corruption during early boot, resulting in kernel instability, data loss, or crashes that affect availability of affected servers and embedded devices.

How an attack unfolds

An attacker with the ability to influence or observe kernel initialization on a vulnerable powerpc build triggers kasan_init_region with a misaligned start address; the resulting out-of-bounds write occurs silently during memblock setup before any later reserve or use of the region.

How to fix it

Update the Linux kernel to a revision containing commit 230e89b5ad0a33f530a2a976b3e5e4385cb27882, which performs page alignment on k_start before memblock_alloc.

How to confirm the fix worked

Inspect the kasan_init_region function in the powerpc KASAN source to confirm k_start is aligned to PAGE_SIZE prior to the memblock_alloc call and that va calculations remain within the allocated block.

Typical attack path

1. Obtain code execution or control sufficient to reach kasan_init_region on powerpc
2. Supply or arrange a k_start value not aligned to PAGE_SIZE
3. Allow the miscalculated va pointer to perform the invalid write during the loop
4. Observe or exploit resulting memory corruption

How to detect it

Review early kernel boot logs on powerpc systems for KASAN or memblock allocation anomalies; no post-boot artifacts are produced by this initialization flaw.

What your security team should do

• Prioritize kernel updates on all powerpc systems that enable KASAN
• Rebuild and redeploy custom kernels with the alignment fix applied
• Include powerpc KASAN boot paths in regression testing after updates