linux-kernel - [PATCH] x86/cmdline: Disable instrumentation of cmdline unconditionally

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Message-Id: <20200906154637.1618112-1-nivedita@alum.mit.edu>
Date:   Sun,  6 Sep 2020 11:46:37 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] x86/cmdline: Disable instrumentation of cmdline unconditionally

On 32-bit, cmdline_find_option_bool() is used before paging is enabled,
from check_loader_disabled_bsp() in the early microcode loader.
Instrumentation options that insert accesses to global data will likely
crash or corrupt memory at this point.

cmdline_find_option{,_bool}() are only used during boot, so
instrumentation is not that useful anyway.

Disable instrumentation unconditionally, and additionally disable:
- GCOV
- UBSAN
- tracing: change -pg -> CC_FLAGS_FTRACE
- STACKLEAK_PLUGIN
- BRANCH_PROFILING

Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 arch/x86/lib/Makefile | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index aa067859a70b..0ad4ae9def44 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -15,17 +15,19 @@ CFLAGS_REMOVE_delay.o = $(CC_FLAGS_FTRACE)
 endif
 
 # Early boot use of cmdline; don't instrument it
-ifdef CONFIG_AMD_MEM_ENCRYPT
+GCOV_PROFILE_cmdline.o    := n
 KCOV_INSTRUMENT_cmdline.o := n
 KASAN_SANITIZE_cmdline.o  := n
+UBSAN_SANITIZE_cmdline.o  := n
 KCSAN_SANITIZE_cmdline.o  := n
 
 ifdef CONFIG_FUNCTION_TRACER
-CFLAGS_REMOVE_cmdline.o = -pg
+CFLAGS_REMOVE_cmdline.o = $(CC_FLAGS_FTRACE)
 endif
 
 CFLAGS_cmdline.o := -fno-stack-protector -fno-jump-tables
-endif
+CFLAGS_cmdline.o += $(DISABLE_STACKLEAK_PLUGIN)
+CFLAGS_cmdline.o += -DDISABLE_BRANCH_PROFILING
 
 inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
 inat_tables_maps = $(srctree)/arch/x86/lib/x86-opcode-map.txt
-- 
2.26.2