On 2/16/21 8:33 PM, Pavel Tatashin wrote:
> Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
> linear map range is not checked correctly.
>
> The start physical address that linear map covers can be actually at the
> end of the range because of randomization. Check that and if so reduce it
> to 0.
>
> This can be verified on QEMU with setting kaslr-seed to ~0ul:
>
> memstart_offset_seed = 0xffff
> START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
> END: __pa(PAGE_END - 1) = 1000bfffffff
This would have tripped the check in mhp_get_pluggable_range()
with errors something like here, which is expected.
Hotplug memory [0x680000000-0x688000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x6c0000000-0x6c8000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x700000000-0x708000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x780000000-0x788000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x7c0000000-0x7c8000000] exceeds maximum addressable range [0x0-0x0]
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
> Tested-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ef7698c4e2f0..0d9c115e427f 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1447,6 +1447,22 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
> struct range arch_get_mappable_range(void)
> {
> struct range mhp_range;
> + u64 start_linear_pa = __pa(_PAGE_OFFSET(vabits_actual));
> + u64 end_linear_pa = __pa(PAGE_END - 1);
> +
> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> + /*
> + * Check for a wrap, it is possible because of randomized linear
> + * mapping the start physical address is actually bigger than
> + * the end physical address. In this case set start to zero
> + * because [0, end_linear_pa] range must still be able to cover
> + * all addressable physical addresses.
> + */
> + if (start_linear_pa > end_linear_pa)
> + start_linear_pa = 0;
> + }
> +
> + WARN_ON(start_linear_pa > end_linear_pa);
>
> /*
> * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
> @@ -1454,8 +1470,9 @@ struct range arch_get_mappable_range(void)
> * range which can be mapped inside this linear mapping range, must
> * also be derived from its end points.
> */
> - mhp_range.start = __pa(_PAGE_OFFSET(vabits_actual));
> - mhp_range.end = __pa(PAGE_END - 1);
> + mhp_range.start = start_linear_pa;
> + mhp_range.end = end_linear_pa;
> +
> return mhp_range;
> }
LGTM.
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
