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   1 From 14d7c92f8df9c0964ae6f8b813c1b3ac38120825 Mon Sep 17 00:00:00 2001
   2 From: Linus Torvalds <torvalds@linux-foundation.org>
   3 Date: Mon, 17 Jun 2024 12:57:03 -0700
   4 Subject: Revert "mm: mmap: allow for the maximum number of bits for randomizing mmap_base by default"
   5
   6 From: Linus Torvalds <torvalds@linux-foundation.org>
   7
   8 commit 14d7c92f8df9c0964ae6f8b813c1b3ac38120825 upstream.
   9
  10 This reverts commit 3afb76a66b5559a7b595155803ce23801558a7a9.
  11
  12 This was a wrongheaded workaround for an issue that had already been
  13 fixed much better by commit 4ef9ad19e176 ("mm: huge_memory: don't force
  14 huge page alignment on 32 bit").
  15
  16 Asking users questions at kernel compile time that they can't make sense
  17 of is not a viable strategy.  And the fact that even the kernel VM
  18 maintainers apparently didn't catch that this "fix" is not a fix any
  19 more pretty much proves the point that people can't be expected to
  20 understand the implications of the question.
  21
  22 It may well be the case that we could improve things further, and that
  23 __thp_get_unmapped_area() should take the mapping randomization into
  24 account even for 64-bit kernels.  Maybe we should not be so eager to use
  25 THP mappings.
  26
  27 But in no case should this be a kernel config option.
  28
  29 Cc: Rafael Aquini <aquini@redhat.com>
  30 Cc: Andrew Morton <akpm@linux-foundation.org>
  31 Cc: Jiri Slaby <jirislaby@kernel.org>
  32 Cc: Suren Baghdasaryan <surenb@google.com>
  33 Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
  34 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  35 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  36 ---
  37  arch/Kconfig |   12 ------------
  38  1 file changed, 12 deletions(-)
  39
  40 --- a/arch/Kconfig
  41 +++ b/arch/Kconfig
  42 @@ -1029,21 +1029,10 @@ config ARCH_MMAP_RND_BITS_MAX
  43  config ARCH_MMAP_RND_BITS_DEFAULT
  44         int
  45
  46 -config FORCE_MAX_MMAP_RND_BITS
  47 -       bool "Force maximum number of bits to use for ASLR of mmap base address"
  48 -       default y if !64BIT
  49 -       help
  50 -         ARCH_MMAP_RND_BITS and ARCH_MMAP_RND_COMPAT_BITS represent the number
  51 -         of bits to use for ASLR and if no custom value is assigned (EXPERT)
  52 -         then the architecture's lower bound (minimum) value is assumed.
  53 -         This toggle changes that default assumption to assume the arch upper
  54 -         bound (maximum) value instead.
  55 -
  56  config ARCH_MMAP_RND_BITS
  57         int "Number of bits to use for ASLR of mmap base address" if EXPERT
  58         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
  59         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
  60 -       default ARCH_MMAP_RND_BITS_MAX if FORCE_MAX_MMAP_RND_BITS
  61         default ARCH_MMAP_RND_BITS_MIN
  62         depends on HAVE_ARCH_MMAP_RND_BITS
  63         help
  64 @@ -1078,7 +1067,6 @@ config ARCH_MMAP_RND_COMPAT_BITS
  65         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
  66         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
  67         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
  68 -       default ARCH_MMAP_RND_COMPAT_BITS_MAX if FORCE_MAX_MMAP_RND_BITS
  69         default ARCH_MMAP_RND_COMPAT_BITS_MIN
  70         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
  71         help