On 04/03/2020 04:28, Anshuman Khandual wrote:
> The arm64 page table dump code can race with concurrent modification of the
> kernel page tables. When a leaf entries are modified concurrently, the dump
> code may log stale or inconsistent information for a VA range, but this is
> otherwise not harmful.
>
> When intermediate levels of table are freed, the dump code will continue to
> use memory which has been freed and potentially reallocated for another
> purpose. In such cases, the dump code may dereference bogus addresses,
> leading to a number of potential problems.
>
> Intermediate levels of table may by freed during memory hot-remove,
> which will be enabled by a subsequent patch. To avoid racing with
> this, take the memory hotplug lock when walking the kernel page table.
>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
Thanks,
Steve
> ---
> arch/arm64/mm/ptdump_debugfs.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c
> index 1f2eae3e988b..d29d722ec3ec 100644
> --- a/arch/arm64/mm/ptdump_debugfs.c
> +++ b/arch/arm64/mm/ptdump_debugfs.c
> @@ -1,5 +1,6 @@
> // SPDX-License-Identifier: GPL-2.0
> #include <linux/debugfs.h>
> +#include <linux/memory_hotplug.h>
> #include <linux/seq_file.h>
>
> #include <asm/ptdump.h>
> @@ -7,7 +8,10 @@
> static int ptdump_show(struct seq_file *m, void *v)
> {
> struct ptdump_info *info = m->private;
> +
> + get_online_mems();
> ptdump_walk(m, info);
> + put_online_mems();
> return 0;
> }
> DEFINE_SHOW_ATTRIBUTE(ptdump);
>
