x86/boot/compressed/64: Set up trampoline memory

This patch clears up trampoline memory and copies trampoline code in
place. It's not yet used though.

Tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180226180451.86788-5-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/boot/compressed/head_64.S

@@ -501,8 +501,9 @@ relocated:
 	jmp	*%rax
 
 	.code32
+ENTRY(trampoline_32bit_src)
 compatible_mode:
-	/* Setup data and stack segments */
+	/* Set up data and stack segments */
 	movl	$__KERNEL_DS, %eax
 	movl	%eax, %ds
 	movl	%eax, %ss

arch/x86/boot/compressed/pgtable.h

@@ -3,9 +3,18 @@
 
 #define TRAMPOLINE_32BIT_SIZE		(2 * PAGE_SIZE)
 
+#define TRAMPOLINE_32BIT_PGTABLE_OFFSET	0
+
+#define TRAMPOLINE_32BIT_CODE_OFFSET	PAGE_SIZE
+#define TRAMPOLINE_32BIT_CODE_SIZE	0x60
+
+#define TRAMPOLINE_32BIT_STACK_END	TRAMPOLINE_32BIT_SIZE
+
 #ifndef __ASSEMBLER__
 
 extern unsigned long *trampoline_32bit;
 
+extern void trampoline_32bit_src(void *return_ptr);
+
 #endif /* __ASSEMBLER__ */
 #endif /* BOOT_COMPRESSED_PAGETABLE_H */

arch/x86/boot/compressed/pgtable_64.c

@@ -76,6 +76,13 @@ struct paging_config paging_prepare(void)
 	/* Preserve trampoline memory */
 	memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
 
+	/* Clear trampoline memory first */
+	memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
+
+	/* Copy trampoline code in place */
+	memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
+			&trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);
+
 	return paging_config;
 }