On Thu, Jun 13, 2024 at 5:39 PM Ilya Leoshkevich [off-list ref] wrote:

x86's alloc_node_data() rounds up node data size to PAGE_SIZE. It's not
explained why it's needed, but it's most likely for performance
reasons, since the padding bytes are not used anywhere. Some other
architectures do it as well, e.g., mips rounds it up to the cache line
size.

kmsan_init_shadow() initializes metadata for each node data and assumes
the x86 rounding, which does not match other architectures. This may
cause the range end to overshoot the end of available memory, in turn
causing virt_to_page_or_null() in kmsan_init_alloc_meta_for_range() to
return NULL, which leads to kernel panic shortly after.

Since the padding bytes are not used, drop the rounding.

Nice catch, thanks!

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>

Reviewed-by: Alexander Potapenko <glider@google.com>