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

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This reverts commit 3afb76a66b.

This was a wrongheaded workaround for an issue that had already been
fixed much better by commit 4ef9ad19e1 ("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>
This commit is contained in:
Linus Torvalds 2024-06-17 12:57:03 -07:00
parent e6b324fbf2
commit 14d7c92f8d
1 changed files with 0 additions and 12 deletions
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12
arch/Kconfig
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@ -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