arm64: raise default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA

Since commit f101c5644771 ("arm64: Support ARM64_VA_BITS=52 when
setting ARCH_MMAP_RND_BITS_MAX"), arm64 supports up to 33, 31, and 29
bits of mmap ASLR entropy on 48-bit and 52-bit virtual address spaces
for 4K, 16K, and 64K pages respectively. However, ARCH_MMAP_RND_BITS
still defaults to ARCH_MMAP_RND_BITS_MIN (18, 16, and 14 bits), which
was set in commit 8f0d3aa9de57 ("arm64: mm: support ARCH_MMAP_RND_BITS")
when 39-bit VA was the 4K default.

Set the default ARCH_MMAP_RND_BITS for 48-bit and 52-bit VA to 28 (4K
pages), 26 (16K pages), and 24 (64K pages), matching x86_64's 1 TiB
randomization range (5 bits below ARCH_MMAP_RND_BITS_MAX) while keeping
ARCH_MMAP_RND_BITS_MIN unchanged for smaller VA configurations.

Closes: https://github.com/KSPP/linux/issues/371
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Iurii Trukhin <yuri@trukhin.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

0 files changed, 0 insertions, 0 deletions