[PATCH] ARM: highmem: avoid clobbering non-page aligned memory reservations

[Ard Biesheuvel]

On Thu, 29 Oct 2020 at 12:03, Ard Biesheuvel <ardb at kernel.org> wrote:
>
> free_highpages() iterates over the free memblock regions in high
> memory, and marks each page as available for the memory management
> system. However, as it rounds the end of each region downwards, we
> may end up freeing a page that is memblock_reserve()d, resulting
> in memory corruption. So align the end of the range to the next
> page instead.
>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  arch/arm/mm/init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index a391804c7ce3..d41781cb5496 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -354,7 +354,7 @@ static void __init free_highpages(void)
>         for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE,
>                                 &range_start, &range_end, NULL) {
>                 unsigned long start = PHYS_PFN(range_start);
> -               unsigned long end = PHYS_PFN(range_end);
> +               unsigned long end = PHYS_PFN(PAGE_ALIGN(range_end));
>

Apologies, this should be

-               unsigned long start = PHYS_PFN(range_start);
+               unsigned long start = PHYS_PFN(PAGE_ALIGN(range_start));
                unsigned long end = PHYS_PFN(range_end);


Strangely enough, the wrong version above also fixed the issue I was
seeing, but it is start that needs rounding up, not end.

>                 /* Ignore complete lowmem entries */
>                 if (end <= max_low)
> --
> 2.17.1
>