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authorKees Cook <keescook@chromium.org>2014-08-06 16:03:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-06 18:01:12 -0700
commit1332429b305044aa75163399ae960c6535828ce6 (patch)
tree22efa40e700b98b423bdc2145f9581a611ea101f /Makefile
parent5838d4442bd5971687b72221736222637e03140d (diff)
downloadlinux-linaro-stable-1332429b305044aa75163399ae960c6535828ce6.tar.gz
./Makefile: explain stack-protector-strong CONFIG logic
This adds a hopefully helpful comment above the (seemingly weird) compiler flag selection logic. Signed-off-by: Kees Cook <keescook@chromium.org> Suggested-by: Andrew Morton <akpm@linux-foundation.org> Cc: Andi Kleen <ak@linux.intel.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Michal Marek <mmarek@suse.cz> Cc: Michal Hocko <mhocko@suse.cz> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile16
1 files changed, 16 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index d0901b46b4bf..af2f2fcfe01c 100644
--- a/Makefile
+++ b/Makefile
@@ -636,6 +636,22 @@ KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
endif
# Handle stack protector mode.
+#
+# Since kbuild can potentially perform two passes (first with the old
+# .config values and then with updated .config values), we cannot error out
+# if a desired compiler option is unsupported. If we were to error, kbuild
+# could never get to the second pass and actually notice that we changed
+# the option to something that was supported.
+#
+# Additionally, we don't want to fallback and/or silently change which compiler
+# flags will be used, since that leads to producing kernels with different
+# security feature characteristics depending on the compiler used. ("But I
+# selected CC_STACKPROTECTOR_STRONG! Why did it build with _REGULAR?!")
+#
+# The middle ground is to warn here so that the failed option is obvious, but
+# to let the build fail with bad compiler flags so that we can't produce a
+# kernel when there is a CONFIG and compiler mismatch.
+#
ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
stackp-flag := -fstack-protector
ifeq ($(call cc-option, $(stackp-flag)),)