3.16.55-rc1 review patch. If anyone has any objections, please let me know.
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From: Linus Torvalds torvalds@linux-foundation.org
commit 3ce120b16cc548472f80cf8644f90eda958cf1b6 upstream.
It appears that hardened gentoo enables "-fstack-check" by default for gcc.
That doesn't work _at_all_ for the kernel, because the kernel stack doesn't act like a user stack at all: it's much smaller, and it doesn't auto-expand on use. So the extra "probe one page below the stack" code generated by -fstack-check just breaks the kernel in horrible ways, causing infinite double faults etc.
[ I have to say, that the particular code gcc generates looks very stupid even for user space where it works, but that's a separate issue. ]
Reported-and-tested-by: Alexander Tsoy alexander@tsoy.me Reported-and-tested-by: Toralf Förster toralf.foerster@gmx.de Cc: Dave Hansen dave.hansen@intel.com Cc: Jiri Kosina jikos@kernel.org Cc: Andy Lutomirski luto@amacapital.net Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- Makefile | 3 +++ 1 file changed, 3 insertions(+)
--- a/Makefile +++ b/Makefile @@ -736,6 +736,9 @@ KBUILD_CFLAGS += $(call cc-disable-warni # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow)
+# Make sure -fstack-check isn't enabled (like gentoo apparently did) +KBUILD_CFLAGS += $(call cc-option,-fno-stack-check,) + # conserve stack if available KBUILD_CFLAGS += $(call cc-option,-fconserve-stack)