x86/mm/sme: Disable stack protection for mem_encrypt_identity.c

Stack protection is not compatible with early boot code.  All of the early
SME boot code is now isolated in a separate file, mem_encrypt_identity.c,
so arch/x86/mm/Makefile can be updated to turn off stack protection for
the entire file.  This eliminates the need to worry about other functions
within the file being instrumented with stack protection (as was seen
when a newer version of GCC instrumented sme_encrypt_kernel() where an
older version hadn't).  It also allows removal of the __nostackprotector
attribute from individual functions.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/20180226232554.14108.16881.stgit@tlendack-t1.amdoffice.net

arch/x86/mm/Makefile

@@ -19,6 +19,7 @@ obj-y	:=  init.o init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \
 nostackp := $(call cc-option, -fno-stack-protector)
 CFLAGS_physaddr.o		:= $(nostackp)
 CFLAGS_setup_nx.o		:= $(nostackp)
+CFLAGS_mem_encrypt_identity.o	:= $(nostackp)
 
 CFLAGS_fault.o := -I$(src)/../include/asm/trace
 

arch/x86/mm/mem_encrypt_identity.c

@@ -266,7 +266,7 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
 	return entries + tables;
 }
 
-void __init __nostackprotector sme_encrypt_kernel(struct boot_params *bp)
+void __init sme_encrypt_kernel(struct boot_params *bp)
 {
 	unsigned long workarea_start, workarea_end, workarea_len;
 	unsigned long execute_start, execute_end, execute_len;
@@ -468,7 +468,7 @@ void __init __nostackprotector sme_encrypt_kernel(struct boot_params *bp)
 	native_write_cr3(__native_read_cr3());
 }
 
-void __init __nostackprotector sme_enable(struct boot_params *bp)
+void __init sme_enable(struct boot_params *bp)
 {
 	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
 	unsigned int eax, ebx, ecx, edx;