x86/mm/mem_encrypt: Disable all instrumentation for early SME setup [Linux 5.1]

x86/mm/mem_encrypt: Disable all instrumentation for early SME setup [Linux 5.1]

This Linux kernel change "x86/mm/mem_encrypt: Disable all instrumentation for early SME setup" is included in the Linux 5.1 release. This change is authored by Gary Hook <Gary.Hook [at] amd.com> on Mon Apr 29 22:22:58 2019 +0000. The commit for this change in Linux stable tree is b51ce37 (patch).

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 <[email protected]>
Signed-off-by: Gary R Hook <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Boris Brezillon <[email protected]>
Cc: Coly Li <[email protected]>
Cc: "[email protected]" <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: "[email protected]" <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: "[email protected]" <[email protected]>
Cc: "[email protected]" <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

There are 23 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/x86/lib/Makefile | 12 ++++++++++++
 lib/Makefile          | 11 +++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 140e618..3cb3af5 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -6,6 +6,18 @@
 # 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     [email protected]
diff --git a/lib/Makefile b/lib/Makefile
index 3b08673..18c2be5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -17,6 +17,17 @@ KCOV_INSTRUMENT_list_debug.o := n
 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 \

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