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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Xen-devel <xen-devel@lists.xenproject.org>
Cc: "Wei Liu" <wl@xen.org>, "Jason Andryuk" <jandryuk@gmail.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Stefan Bader" <stefan.bader@canonical.com>,
	"Jan Beulich" <JBeulich@suse.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: [PATCH] x86/build: Unilaterally disable -fcf-protection
Date: Tue, 12 May 2020 20:11:16 +0100	[thread overview]
Message-ID: <20200512191116.6851-1-andrew.cooper3@citrix.com> (raw)

See comment for details.  Works around a GCC-9 bug which breaks the build on
Ubuntu.

Reported-by: Jason Andryuk <jandryuk@gmail.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Jason Andryuk <jandryuk@gmail.com>
CC: Stefan Bader <stefan.bader@canonical.com>

Sorry for messing you around with how to fix this.  I'd neglected to consider
the CONFIG_LIVEPATCH interaction.  With that extra observation, there is no
point having the extra complexity given that the result with CET-IBT and
Retpoline still isn't usable.
---
 xen/arch/x86/arch.mk         | 9 +++++++++
 xen/arch/x86/boot/build32.mk | 1 +
 2 files changed, 10 insertions(+)

diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index 2a51553edb..93e30e4bea 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -67,6 +67,15 @@ CFLAGS-$(CONFIG_INDIRECT_THUNK) += -mindirect-branch=thunk-extern
 CFLAGS-$(CONFIG_INDIRECT_THUNK) += -mindirect-branch-register
 CFLAGS-$(CONFIG_INDIRECT_THUNK) += -fno-jump-tables
 
+# Xen doesn't support CET-IBT yet.  At a minimum, logic is required to
+# enable it for supervisor use, but the Livepatch functionality needs
+# to learn not to overwrite ENDBR64 instructions.
+#
+# Furthermore, Ubuntu enables -fcf-protection by default, along with a
+# buggy version of GCC-9 which objects to it in combination with
+# -mindirect-branch=thunk-extern (Fixed in GCC 10, 9.4).
+$(call cc-option-add,CFLAGS,CC,-fcf-protection=none)
+
 # If supported by the compiler, reduce stack alignment to 8 bytes. But allow
 # this to be overridden elsewhere.
 $(call cc-option-add,CFLAGS-stack-boundary,CC,-mpreferred-stack-boundary=3)
diff --git a/xen/arch/x86/boot/build32.mk b/xen/arch/x86/boot/build32.mk
index 48c7407c00..5a00755512 100644
--- a/xen/arch/x86/boot/build32.mk
+++ b/xen/arch/x86/boot/build32.mk
@@ -3,6 +3,7 @@ CFLAGS =
 include $(XEN_ROOT)/Config.mk
 
 $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
+$(call cc-option-add,CFLAGS,CC,-fcf-protection=none)
 
 CFLAGS += -Werror -fno-asynchronous-unwind-tables -fno-builtin -g0 -msoft-float
 CFLAGS += -I$(XEN_ROOT)/xen/include
-- 
2.11.0



             reply	other threads:[~2020-05-12 19:12 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-12 19:11 Andrew Cooper [this message]
2020-05-13  2:35 ` [PATCH] x86/build: Unilaterally disable -fcf-protection Jason Andryuk
2020-05-13 11:01   ` Andrew Cooper
2020-05-13 12:15     ` Jason Andryuk
2020-05-13  9:15 ` Jan Beulich
2020-05-13 13:55 [PATCH] build: Fix build with Ubuntu Andrew Cooper
2020-05-13 13:55 ` [PATCH] x86/build: Unilaterally disable -fcf-protection Andrew Cooper
2020-05-13 14:13   ` Jan Beulich
2020-05-13 14:40     ` Andrew Cooper
2020-05-13 14:54   ` Jason Andryuk

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