6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rafael Aquini <aquini@xxxxxxxxxx> commit 3afb76a66b5559a7b595155803ce23801558a7a9 upstream. 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@xxxxxxxxxxxxxxxxxxxx: default to `y' if 32-bit, per Rafael] Link: https://lkml.kernel.org/r/20240606180622.102099-1-aquini@xxxxxxxxxx Fixes: 1854bc6e2420 ("mm/readahead: Align file mappings for non-DAX") Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Petr Mladek <pmladek@xxxxxxxx> Cc: Samuel Holland <samuel.holland@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/Kconfig | 12 ++++++++++++ 1 file changed, 12 insertions(+) --- a/arch/Kconfig +++ b/arch/Kconfig @@ -1037,10 +1037,21 @@ 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 @@ -1075,6 +1086,7 @@ 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
