linux-kernel - [PATCH 5.5 64/65] ARM: 8961/2: Fix Kbuild issue caused by per-task stack protector GCC plugin

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Date:   Thu, 19 Mar 2020 14:04:46 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Merlijn Wajer <merlijn@...zup.org>,
        Tony Lindgren <tony@...mide.com>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: [PATCH 5.5 64/65] ARM: 8961/2: Fix Kbuild issue caused by per-task stack protector GCC plugin

From: Ard Biesheuvel <ardb@...nel.org>

commit 89604523a76eb3e13014b2bdab7f8870becee284 upstream.

When using plugins, GCC requires that the -fplugin= options precedes
any of its plugin arguments appearing on the command line as well.
This is usually not a concern, but as it turns out, this requirement
is causing some issues with ARM's per-task stack protector plugin
and Kbuild's implementation of $(cc-option).

When the per-task stack protector plugin is enabled, and we tweak
the implementation of cc-option not to pipe the stderr output of
GCC to /dev/null, the following output is generated when GCC is
executed in the context of cc-option:

  cc1: error: plugin arm_ssp_per_task_plugin should be specified before \
         -fplugin-arg-arm_ssp_per_task_plugin-tso=1 in the command line
  cc1: error: plugin arm_ssp_per_task_plugin should be specified before \
         -fplugin-arg-arm_ssp_per_task_plugin-offset=24 in the command line

These errors will cause any option passed to cc-option to be treated
as unsupported, which is obviously incorrect.

The cause of this issue is the fact that the -fplugin= argument is
added to GCC_PLUGINS_CFLAGS, whereas the arguments above are added
to KBUILD_CFLAGS, and the contents of the former get filtered out of
the latter before being passed to the GCC running the cc-option test,
and so the -fplugin= option does not appear at all on the GCC command
line.

Adding the arguments to GCC_PLUGINS_CFLAGS instead of KBUILD_CFLAGS
would be the correct approach here, if it weren't for the fact that we
are using $(eval) to defer the moment that they are added until after
asm-offsets.h is generated, which is after the point where the contents
of GCC_PLUGINS_CFLAGS are added to KBUILD_CFLAGS. So instead, we have
to add our plugin arguments to both.

For similar reasons, we cannot append DISABLE_ARM_SSP_PER_TASK_PLUGIN
to KBUILD_CFLAGS, as it will be passed to GCC when executing in the
context of cc-option, whereas the other plugin arguments will have
been filtered out, resulting in a similar error and false negative
result as above. So add it to ccflags-y instead.

Fixes: 189af4657186da08 ("ARM: smp: add support for per-task stack canaries")
Reported-by: Merlijn Wajer <merlijn@...zup.org>
Tested-by: Tony Lindgren <tony@...mide.com>
Acked-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm/Makefile                 |    4 +++-
 arch/arm/boot/compressed/Makefile |    4 ++--
 2 files changed, 5 insertions(+), 3 deletions(-)

--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -307,13 +307,15 @@ endif
 ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
 prepare: stack_protector_prepare
 stack_protector_prepare: prepare0
-	$(eval KBUILD_CFLAGS += \
+	$(eval SSP_PLUGIN_CFLAGS := \
 		-fplugin-arg-arm_ssp_per_task_plugin-tso=$(shell	\
 			awk '{if ($$2 == "THREAD_SZ_ORDER") print $$3;}'\
 				include/generated/asm-offsets.h)	\
 		-fplugin-arg-arm_ssp_per_task_plugin-offset=$(shell	\
 			awk '{if ($$2 == "TI_STACK_CANARY") print $$3;}'\
 				include/generated/asm-offsets.h))
+	$(eval KBUILD_CFLAGS += $(SSP_PLUGIN_CFLAGS))
+	$(eval GCC_PLUGINS_CFLAGS += $(SSP_PLUGIN_CFLAGS))
 endif

 all:	$(notdir $(KBUILD_IMAGE))
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -101,7 +101,6 @@ clean-files += piggy_data lib1funcs.S as
 		$(libfdt) $(libfdt_hdrs) hyp-stub.S

 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
-KBUILD_CFLAGS += $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)

 ifeq ($(CONFIG_FUNCTION_TRACER),y)
 ORIG_CFLAGS := $(KBUILD_CFLAGS)
@@ -117,7 +116,8 @@ CFLAGS_fdt_ro.o := $(nossp_flags)
 CFLAGS_fdt_rw.o := $(nossp_flags)
 CFLAGS_fdt_wip.o := $(nossp_flags)

-ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin -I$(obj)
+ccflags-y := -fpic $(call cc-option,-mno-single-pic-base,) -fno-builtin \
+	     -I$(obj) $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)
 asflags-y := -DZIMAGE

 # Supply kernel BSS size to the decompressor via a linker symbol.