x86/mm/mem_encrypt: Disable all instrumentation for early SME setup

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 it cannot be assumed 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.

[ bp: Get rid of intermediary nostackp var and cleanup whitespace. ]

Fixes: aca20d546214 ("x86/mm: Add support to make use of Secure Memory Encryption")
Reported-by: Li RongQing <[e-mail]>
Signed-off-by: Gary R Hook <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Andy Shevchenko <[e-mail]>
Cc: Boris Brezillon <[e-mail]>
Cc: Coly Li <[e-mail]>
Cc: "[e-mail]" <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Kent Overstreet <[e-mail]>
Cc: "[e-mail]" <[e-mail]>
Cc: Masahiro Yamada <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: "[e-mail]" <[e-mail]>
Cc: "[e-mail]" <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: x86-ml <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/lib/Makefile

···
 # Produces uninteresting flaky coverage.
 KCOV_INSTRUMENT_delay.o	:= n
 
+# Early boot use of cmdline; don't instrument it
+ifdef CONFIG_AMD_MEM_ENCRYPT
+KCOV_INSTRUMENT_cmdline.o := n
+KASAN_SANITIZE_cmdline.o  := n
+
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_cmdline.o = -pg
+endif
+
+CFLAGS_cmdline.o := $(call cc-option, -fno-stack-protector)
+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     $@

lib/Makefile

···
 KCOV_INSTRUMENT_debugobjects.o := n
 KCOV_INSTRUMENT_dynamic_debug.o := n
 
+# Early boot use of cmdline, don't instrument it
+ifdef CONFIG_AMD_MEM_ENCRYPT
+KASAN_SANITIZE_string.o := n
+
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_string.o = -pg
+endif
+
+CFLAGS_string.o := $(call cc-option, -fno-stack-protector)
+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 \