[PATCH] arm64: mm: Fix lockless walks with static and dynamic page-table folding

[Will Deacon]

On Thu, 25 Jul 2024 10:03:45 +0100, Will Deacon wrote:
> Lina reports random oopsen originating from the fast GUP code when
> 16K pages are used with 4-level page-tables, the fourth level being
> folded at runtime due to lack of LPA2.
> 
> In this configuration, the generic implementation of
> p4d_offset_lockless() will return a 'p4d_t *' corresponding to the
> 'pgd_t' allocated on the stack of the caller, gup_fast_pgd_range().
> This is normally fine, but when the fourth level of page-table is folded
> at runtime, pud_offset_lockless() will offset from the address of the
> 'p4d_t' to calculate the address of the PUD in the same page-table page.
> This results in a stray stack read when the 'p4d_t' has been allocated
> on the stack and can send the walker into the weeds.
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64: mm: Fix lockless walks with static and dynamic page-table folding
      https://git.kernel.org/arm64/c/36639013b346

Cheers,
-- 
Will

https://fixes.arm64.dev
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