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Patch "kbuild: add '-fno-stack-check' to kernel build options" has been added to the 3.18-stable tree

PATCH [email protected] 1 participant 1 message Dec 31, 2017

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This is a note to let you know that I've just added the patch titled

kbuild: add '-fno-stack-check' to kernel build options

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kbuild-add-fno-stack-check-to-kernel-build-options.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 3ce120b16cc548472f80cf8644f90eda958cf1b6 Mon Sep 17 00:00:00 2001

From: Linus Torvalds <[email protected]>
Date: Fri, 29 Dec 2017 17:34:43 -0800
Subject: kbuild: add '-fno-stack-check' to kernel build options
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From: Linus Torvalds <[email protected]>

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 <[email protected]>
Reported-and-tested-by Toralf Förster <[email protected]>
Cc Dave Hansen <[email protected]>
Cc Jiri Kosina <[email protected]>
Cc Andy Lutomirski <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 Makefile |    3 +++
 1 file changed, 3 insertions(+)
Makefile +3 -0
@@ -762,6 +762,9 @@ 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)

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/kbuild-add-fno-stack-check-to-kernel-build-options.patch