alloc_tag: fix module allocation tags populated area calculation

alloc_tag: fix module allocation tags populated area calculation

vm_module_tags_populate() calculation of the populated area assumes that
area starts at a page boundary and therefore when new pages are allocation,
the end of the area is page-aligned as well. If the start of the area is
not page-aligned then allocating a page and incrementing the end of the
area by PAGE_SIZE leads to an area at the end but within the area boundary
which is not populated. Accessing this are will lead to a kernel panic.
Fix the calculation by down-aligning the start of the area and using that
as the location allocated pages are mapped to.

[gehao@kylinos.cn: fix vm_module_tags_populate's KASAN poisoning logic]
Link: https://lkml.kernel.org/r/20241205170528.81000-1-hao.ge@linux.dev
[gehao@kylinos.cn: fix panic when CONFIG_KASAN enabled and CONFIG_KASAN_VMALLOC not enabled]
Link: https://lkml.kernel.org/r/20241212072126.134572-1-hao.ge@linux.dev
Link: https://lkml.kernel.org/r/20241130001423.1114965-1-surenb@google.com
Fixes: 0f9b685626da ("alloc_tag: populate memory for module tags as needed")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202411132111.6a221562-lkp@intel.com
Acked-by: Yu Zhao <yuzhao@google.com>
Tested-by: Adrian Huang <ahuang12@lenovo.com>
Cc: David Wang <00107082@163.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Sourav Panda <souravpanda@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>