Commit 161ce69c2c89 for kernel

commit 161ce69c2c89781784b945d8e281ff2da9dede9c
Author: Denis M. Karpov <komlomal@gmail.com>
Date:   Thu Apr 9 13:33:45 2026 +0300

    userfaultfd: allow registration of ranges below mmap_min_addr

    The current implementation of validate_range() in fs/userfaultfd.c
    performs a hard check against mmap_min_addr.  This is redundant because
    UFFDIO_REGISTER operates on memory ranges that must already be backed by a
    VMA.

    Enforcing mmap_min_addr or capability checks again in userfaultfd is
    unnecessary and prevents applications like binary compilers from using
    UFFD for valid memory regions mapped by application.

    Remove the redundant check for mmap_min_addr.

    We started using UFFD instead of the classic mprotect approach in the
    binary translator to track application writes.  During development, we
    encountered this bug.  The translator cannot control where the translated
    application chooses to map its memory and if the app requires a
    low-address area, UFFD fails, whereas mprotect would work just fine.  I
    believe this is a genuine logic bug rather than an improvement, and I
    would appreciate including the fix in stable.

    Link: https://lore.kernel.org/20260409103345.15044-1-komlomal@gmail.com
    Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization")
    Signed-off-by: Denis M. Karpov <komlomal@gmail.com>
    Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
    Acked-by: Harry Yoo (Oracle) <harry@kernel.org>
    Reviewed-by: Pedro Falcato <pfalcato@suse.de>
    Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
    Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Christian Brauner <brauner@kernel.org>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Jann Horn <jannh@google.com>
    Cc: Peter Xu <peterx@redhat.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index bdc84e5219cd..4b53dc4a3266 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1238,8 +1238,6 @@ static __always_inline int validate_unaligned_range(
 		return -EINVAL;
 	if (!len)
 		return -EINVAL;
-	if (start < mmap_min_addr)
-		return -EINVAL;
 	if (start >= task_size)
 		return -EINVAL;
 	if (len > task_size - start)