diff options
| author | Rafael Aquini <[email protected]> | 2024-06-06 14:06:22 -0400 |
|---|---|---|
| committer | Andrew Morton <[email protected]> | 2024-06-15 10:43:06 -0700 |
| commit | 3afb76a66b5559a7b595155803ce23801558a7a9 (patch) | |
| tree | a9ad68a96db16bf98cbafb486d001a83b55c0cf9 | |
| parent | c1558bc57b8e5b4da5d821537cd30e2e660861d8 (diff) | |
mm: mmap: allow for the maximum number of bits for randomizing mmap_base by default
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/
[[email protected]: default to `y' if 32-bit, per Rafael]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 1854bc6e2420 ("mm/readahead: Align file mappings for non-DAX")
Signed-off-by: Rafael Aquini <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Mike Rapoport (IBM) <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Samuel Holland <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
| -rw-r--r-- | arch/Kconfig | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index 975dd22a2dbd..3e2a63772b3d 100644 --- a/arch/Kconfig +++ b/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 |