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perf: arm_spe: Make wakeup range check overflow safe

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The current code checks whether the wakeup point is in the current
writable range by comparing it with handle->head + handle->size.

The perf AUX head is a monotonically increasing index, so that addition
can overflow when head is close to ULONG_MAX. In that case, a wakeup
point which is still inside the free space range can be missed.

Use unsigned subtraction to compare the distance from head to wakeup
against the handle->size. This can dismiss the issue when addition
overflow.

This is unlikely to happen in practice, but the change makes the
watermark check logically correct.

Fixes: d5d9696b03 ("drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension")
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Leo Yan
2026-07-02 18:05:21 +01:00
committed by Will Deacon
parent 49f2413f9b
commit fcc5eaea2d
1 changed files with 1 additions and 1 deletions
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drivers/perf/arm_spe_pmu.c
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@@ -577,7 +577,7 @@ static u64 __arm_spe_pmu_next_off(struct perf_output_handle *handle)
* the page boundary following it. Keep the tail boundary if
* that's lower.
*/
if (handle->wakeup < (handle->head + handle->size) && head <= wakeup)
if ((handle->wakeup - handle->head) < handle->size && head <= wakeup)
limit = min(limit, round_up(wakeup, PAGE_SIZE));
if (limit > head)