The quilt patch titled Subject: mm: mmap: allow for the maximum number of bits for randomizing mmap_base by default has been removed from the -mm tree. Its filename was mm-mmap-allow-for-the-maximum-number-of-bits-for-randomizing-mmap_base-by-default.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------ From: Rafael Aquini aquini@redhat.com Subject: mm: mmap: allow for the maximum number of bits for randomizing mmap_base by default Date: Thu, 6 Jun 2024 14:06:22 -0400
An ASLR regression was noticed [1] and tracked down to file-mapped areas being backed by THP in recent kernels. The 21-bit alignment constraint for such mappings reduces the entropy for randomizing the placement of 64-bit library mappings and breaks ASLR completely for 32-bit libraries.
The reported issue is easily addressed by increasing vm.mmap_rnd_bits and vm.mmap_rnd_compat_bits. This patch just provides a simple way to set ARCH_MMAP_RND_BITS and ARCH_MMAP_RND_COMPAT_BITS to their maximum values allowed by the architecture at build time.
[1] https://zolutal.github.io/aslrnt/
[akpm@linux-foundation.org: default to `y' if 32-bit, per Rafael] Link: https://lkml.kernel.org/r/20240606180622.102099-1-aquini@redhat.com Fixes: 1854bc6e2420 ("mm/readahead: Align file mappings for non-DAX") Signed-off-by: Rafael Aquini aquini@redhat.com Cc: Arnd Bergmann arnd@arndb.de Cc: Heiko Carstens hca@linux.ibm.com Cc: Mike Rapoport (IBM) rppt@kernel.org Cc: Paul E. McKenney paulmck@kernel.org Cc: Petr Mladek pmladek@suse.com Cc: Samuel Holland samuel.holland@sifive.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
arch/Kconfig | 12 ++++++++++++ 1 file changed, 12 insertions(+)
--- a/arch/Kconfig~mm-mmap-allow-for-the-maximum-number-of-bits-for-randomizing-mmap_base-by-default +++ a/arch/Kconfig @@ -1046,10 +1046,21 @@ config ARCH_MMAP_RND_BITS_MAX config ARCH_MMAP_RND_BITS_DEFAULT int
+config FORCE_MAX_MMAP_RND_BITS + bool "Force maximum number of bits to use for ASLR of mmap base address" + default y if !64BIT + help + ARCH_MMAP_RND_BITS and ARCH_MMAP_RND_COMPAT_BITS represent the number + of bits to use for ASLR and if no custom value is assigned (EXPERT) + then the architecture's lower bound (minimum) value is assumed. + This toggle changes that default assumption to assume the arch upper + bound (maximum) value instead. + config ARCH_MMAP_RND_BITS int "Number of bits to use for ASLR of mmap base address" if EXPERT range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT + default ARCH_MMAP_RND_BITS_MAX if FORCE_MAX_MMAP_RND_BITS default ARCH_MMAP_RND_BITS_MIN depends on HAVE_ARCH_MMAP_RND_BITS help @@ -1084,6 +1095,7 @@ config ARCH_MMAP_RND_COMPAT_BITS int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT + default ARCH_MMAP_RND_COMPAT_BITS_MAX if FORCE_MAX_MMAP_RND_BITS default ARCH_MMAP_RND_COMPAT_BITS_MIN depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS help _
Patches currently in -mm which might be from aquini@redhat.com are