linux-kernel - [PATCH 2] x86/mm/mem_encrypt: Disable all instrumentation for SME early files

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Date:   Mon, 29 Apr 2019 22:22:58 +0000
From:   "Hook, Gary" <Gary.Hook@....com>
To:     "x86@...nel.org" <x86@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "luto@...nel.org" <luto@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: [PATCH 2] x86/mm/mem_encrypt: Disable all instrumentation for SME
 early files

Enablement of AMD's Secure Memory Encryption feature is determined
very early after start_kernel() is entered. Part of this procedure
involves scanning the command line for the parameter 'mem_encrypt'.

To determine intended state, the function sme_enable() uses library
functions cmdline_find_option() and strncmp().  Their use occurs early
enough such that we can't assume that any instrumentation subsystem is
initialized. For example, making calls to a KASAN-instrumented
function before KASAN is set up will result in the use of uninitialized
memory and a boot failure.

When AMD's SME support is enabled, conditionally disable instrumentation
of these dependent functions in lib/string.c and arch/x86/lib/cmdline.c.

Fixes: aca20d546214  ("x86/mm: Add support to make use of Secure Memory Encryption")
Reported-by: Li RongQing <lirongqing@...du.com>
Signed-off-by: Gary R Hook <gary.hook@....com>
---
 arch/x86/lib/Makefile |   16 ++++++++++++++++
 lib/Makefile          |   14 ++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 140e61843a07..b5b932124280 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -6,6 +6,22 @@
 # Produces uninteresting flaky coverage.
 KCOV_INSTRUMENT_delay.o	:= n
 
+ifdef CONFIG_AMD_MEM_ENCRYPT
+#
+# Early boot use of cmdline; don't instrument it
+#
+KCOV_INSTRUMENT_cmdline.o              := n
+
+KASAN_SANITIZE_cmdline.o               := n
+
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_cmdline.o                        = -pg
+endif
+
+nostackp := $(call cc-option, -fno-stack-protector)
+CFLAGS_cmdline.o               := $(nostackp)
+endif
+
 inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
 inat_tables_maps = $(srctree)/arch/x86/lib/x86-opcode-map.txt
 quiet_cmd_inat_tables = GEN     $@
diff --git a/lib/Makefile b/lib/Makefile
index 3b08673e8881..07d71662f6b2 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -17,6 +17,20 @@ KCOV_INSTRUMENT_list_debug.o := n
 KCOV_INSTRUMENT_debugobjects.o := n
 KCOV_INSTRUMENT_dynamic_debug.o := n
 
+ifdef CONFIG_AMD_MEM_ENCRYPT
+#
+# Early boot use of cmdline, don't instrument it
+#
+KASAN_SANITIZE_string.o                := n
+
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_string.o         = -pg
+endif
+
+nostackp := $(call cc-option, -fno-stack-protector)
+CFLAGS_string.o                        := $(nostackp)
+endif
+
 lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 rbtree.o radix-tree.o timerqueue.o xarray.o \
 	 idr.o int_sqrt.o extable.o \