releases/4.14.11/kbuild-add-fno-stack-check-to-kernel-build-options.patch

   1 From 3ce120b16cc548472f80cf8644f90eda958cf1b6 Mon Sep 17 00:00:00 2001
   2 From: Linus Torvalds <torvalds@linux-foundation.org>
   3 Date: Fri, 29 Dec 2017 17:34:43 -0800
   4 Subject: kbuild: add '-fno-stack-check' to kernel build options
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   8
   9 From: Linus Torvalds <torvalds@linux-foundation.org>
  10
  11 commit 3ce120b16cc548472f80cf8644f90eda958cf1b6 upstream.
  12
  13 It appears that hardened gentoo enables "-fstack-check" by default for
  14 gcc.
  15
  16 That doesn't work _at_all_ for the kernel, because the kernel stack
  17 doesn't act like a user stack at all: it's much smaller, and it doesn't
  18 auto-expand on use.  So the extra "probe one page below the stack" code
  19 generated by -fstack-check just breaks the kernel in horrible ways,
  20 causing infinite double faults etc.
  21
  22 [ I have to say, that the particular code gcc generates looks very
  23   stupid even for user space where it works, but that's a separate
  24   issue.  ]
  25
  26 Reported-and-tested-by: Alexander Tsoy <alexander@tsoy.me>
  27 Reported-and-tested-by: Toralf Förster <toralf.foerster@gmx.de>
  28 Cc: Dave Hansen <dave.hansen@intel.com>
  29 Cc: Jiri Kosina <jikos@kernel.org>
  30 Cc: Andy Lutomirski <luto@amacapital.net>
  31 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  32 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  33
  34 ---
  35  Makefile |    3 +++
  36  1 file changed, 3 insertions(+)
  37
  38 --- a/Makefile
  39 +++ b/Makefile
  40 @@ -802,6 +802,9 @@ KBUILD_CFLAGS += $(call cc-disable-warni
  41  # disable invalid "can't wrap" optimizations for signed / pointers
  42  KBUILD_CFLAGS  += $(call cc-option,-fno-strict-overflow)
  43
  44 +# Make sure -fstack-check isn't enabled (like gentoo apparently did)
  45 +KBUILD_CFLAGS  += $(call cc-option,-fno-stack-check,)
  46 +
  47  # conserve stack if available
  48  KBUILD_CFLAGS   += $(call cc-option,-fconserve-stack)
  49