linux-kernel - [PATCH v3 2/2] x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20190723212418.36379-2-ndesaulniers@google.com>
Date:   Tue, 23 Jul 2019 14:24:11 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     peterz@...radead.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org, yamada.masahiro@...ionext.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org,
        Vaibhav Rustagi <vaibhavrustagi@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: [PATCH v3 2/2] x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS

KBUILD_CFLAGS is very carefully built up in the top level Makefile,
particularly when cross compiling or using different build tools.
Resetting KBUILD_CFLAGS via := assignment is an antipattern.

The comment above the reset mentions that -pg is problematic.  Other
Makefiles use `CFLAGS_REMOVE_file.o = $(CC_FLAGS_FTRACE)` when
CONFIG_FUNCTION_TRACER is set. Prefer that pattern to wiping out all of
the important KBUILD_CFLAGS then manually having to re-add them. Seems
also that __stack_chk_fail references are generated when using
CONFIG_STACKPROTECTOR or CONFIG_STACKPROTECTOR_STRONG.

Cc: stable@...r.kernel.org
Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality")
Reported-by: Vaibhav Rustagi <vaibhavrustagi@...gle.com>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Alternatively, we could put these in all in one variable and remove it
without any conditional checks (I think that's ok to do so with
CFLAGS_REMOVE).

Changes v2 -> v3:
* Prefer $(CC_FLAGS_FTRACE) which is exported to -pg.
* Also check CONFIG_STACKPROTECTOR and CONFIG_STACKPROTECTOR_STRONG.
* Cc stable.
Changes v1 -> v2:
Rather than manually add -mno-sse, -mno-mmx, -mno-sse2, prefer to filter
-pg flags.

 arch/x86/purgatory/Makefile | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 91ef244026d2..6ef0ced59b9c 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -20,11 +20,27 @@ KCOV_INSTRUMENT := n
 
 # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
 # in turn leaves some undefined symbols like __fentry__ in purgatory and not
-# sure how to relocate those. Like kexec-tools, use custom flags.
-
-KBUILD_CFLAGS := -fno-strict-aliasing -Wall -Wstrict-prototypes -fno-zero-initialized-in-bss -fno-builtin -ffreestanding -c -Os -mcmodel=large
-KBUILD_CFLAGS += -m$(BITS)
-KBUILD_CFLAGS += $(call cc-option,-fno-PIE)
+# sure how to relocate those.
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_sha256.o += $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_purgatory.o += $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_string.o += $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_kexec-purgatory.o += $(CC_FLAGS_FTRACE)
+endif
+
+ifdef CONFIG_STACKPROTECTOR
+CFLAGS_REMOVE_sha256.o += -fstack-protector
+CFLAGS_REMOVE_purgatory.o += -fstack-protector
+CFLAGS_REMOVE_string.o += -fstack-protector
+CFLAGS_REMOVE_kexec-purgatory.o += -fstack-protector
+endif
+
+ifdef CONFIG_STACKPROTECTOR_STRONG
+CFLAGS_REMOVE_sha256.o += -fstack-protector-strong
+CFLAGS_REMOVE_purgatory.o += -fstack-protector-strong
+CFLAGS_REMOVE_string.o += -fstack-protector-strong
+CFLAGS_REMOVE_kexec-purgatory.o += -fstack-protector-strong
+endif
 
 $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
 		$(call if_changed,ld)
-- 
2.22.0.709.g102302147b-goog