powerpc/powernv/memtrace: Fix out of bounds issue in memtrace mmap

powerpc/powernv/memtrace: Fix out of bounds issue in memtrace mmap

[ Upstream commit cd097df4596f3a1e9d75eb8520162de1eb8485b2 ]

memtrace mmap issue has an out of bounds issue. This patch fixes the by
checking that the requested mapping region size should stay within the
allocated region size.

Reported-by: Jonathan Greental <yonatan02greental@gmail.com>
Fixes: 08a022ad3dfa ("powerpc/powernv/memtrace: Allow mmaping trace buffers")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250610021227.361980-1-maddy@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>