From: Kees Cook <keescook@chromium•org>
To: Andrew Morton <akpm@linux-foundation•org>
Cc: Andi Kleen <ak@linux•intel.com>,
Randy Dunlap <rdunlap@infradead•org>,
linux-next@vger•kernel.org, sfr@canb•auug.org.au, mhocko@suse•cz,
linux-kernel@vger•kernel.org, Michal Marek <mmarek@suse•cz>,
linux-kbuild@vger•kernel.org
Subject: [PATCH] kbuild: explain stack-protector-strong CONFIG logic
Date: Wed, 2 Jul 2014 18:10:59 -0700 [thread overview]
Message-ID: <20140703011059.GA6331@www.outflux.net> (raw)
In-Reply-To: <20140702175635.79d54c44.akpm@linux-foundation.org>
This adds a hopefully helpful comment above the (seemingly weird)
compiler flag selection logic.
Suggested-by: Andrew Morton <akpm@linux-foundation•org>
Signed-off-by: Kees Cook <keescook@chromium•org>
---
Makefile | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/Makefile b/Makefile
index 13175632137f..ea88e68d121e 100644
--- a/Makefile
+++ b/Makefile
@@ -630,6 +630,22 @@ 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, $(stackp-flag)),)
--
1.7.9.5
--
Kees Cook
Chrome OS Security
next prev parent reply other threads:[~2014-07-03 1:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-02 22:08 mmotm 2014-07-02-15-07 uploaded akpm
2014-07-02 23:21 ` mmotm 2014-07-02-15-07 uploaded (stack protector) Randy Dunlap
2014-07-03 0:22 ` Andi Kleen
2014-07-03 0:37 ` Randy Dunlap
2014-07-03 0:51 ` Kees Cook
2014-07-03 0:56 ` Andrew Morton
2014-07-03 1:10 ` Kees Cook [this message]
2014-07-03 1:00 ` Andi Kleen
2014-07-03 1:13 ` Kees Cook
2014-07-03 0:57 ` Kees Cook
2014-07-03 1:42 ` Randy Dunlap
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20140703011059.GA6331@www.outflux.net \
--to=keescook@chromium$(echo .)org \
--cc=ak@linux$(echo .)intel.com \
--cc=akpm@linux-foundation$(echo .)org \
--cc=linux-kbuild@vger$(echo .)kernel.org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linux-next@vger$(echo .)kernel.org \
--cc=mhocko@suse$(echo .)cz \
--cc=mmarek@suse$(echo .)cz \
--cc=rdunlap@infradead$(echo .)org \
--cc=sfr@canb$(echo .)auug.org.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox