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ae6bcc6fed
commit 161ce69c2c89781784b945d8e281ff2da9dede9c upstream.
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: 86039bd3b4 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ulrich Hecht <uli@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.