CVE-2026-98176 — drm/amdkfd: Avoid integer underflow with ffs in EOP ring size calc

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

drm/amdkfd: Avoid integer underflow with ffs in EOP ring size calc

The low 6 bits of cp_hqd_eop_control store the base-2 logarithm of the EOP ring size. This was calculated as

ffs(q->eop_ring_buffer_size / sizeof(unsigned int)) - 1 - 1

But ffs can in theory return 1 or 0, so this could underflow (although in practice the ring buffer size cannot be less than 4096).

Change this to

ffs(q->eop_ring_buffer_size / sizeof(unsigned int) / 4)

using properties of logarithms.

(cherry picked from commit 4f18c56630383c14bfc6b2d65f88f2f895d2121a)

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