Revert "mm: mmap: allow for the maximum number of bits for randomizing mmap_base...

This reverts commit 3afb76a66b5559a7b595155803ce23801558a7a9.

This was a wrongheaded workaround for an issue that had already been
fixed much better by commit 4ef9ad19e176 ("mm: huge_memory: don't force
huge page alignment on 32 bit").

Asking users questions at kernel compile time that they can't make sense
of is not a viable strategy.  And the fact that even the kernel VM
maintainers apparently didn't catch that this "fix" is not a fix any
more pretty much proves the point that people can't be expected to
understand the implications of the question.

It may well be the case that we could improve things further, and that
__thp_get_unmapped_area() should take the mapping randomization into
account even for 64-bit kernels.  Maybe we should not be so eager to use
THP mappings.

But in no case should this be a kernel config option.

Cc: Rafael Aquini <aquini@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/Kconfig b/arch/Kconfig
index 3e2a63772b3db1d78a554de88e5655471b6f0e63..975dd22a2dbd22dc1fa7ef727149d99e5ebcbe0a 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1046,21 +1046,10 @@ 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
@@ -1095,7 +1084,6 @@ 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