[PATCHv2 3/5] x86/boot/compressed/64: Save and restore trampoline memory

[Kirill A. Shutemov]

The memory area we found for trampoline shouldn't contain anything
useful. But let's preserve the data anyway. Just to be on safe side.

paging_prepare() would save the data into a buffer.

cleanup_trampoline() would restore it back once we are done with the
trampoline.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Tested-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/boot/compressed/head_64.S    | 10 ++++++++++
 arch/x86/boot/compressed/pgtable_64.c | 13 +++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index d598d65db32c..8ba0582c65d5 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -355,6 +355,16 @@ ENTRY(startup_64)
 	lretq
 lvl5:
 
+	/*
+	 * cleanup_trampoline() would restore trampoline memory.
+	 *
+	 * RSI holds real mode data and needs to be preserved across
+	 * this function call.
+	 */
+	pushq	%rsi
+	call	cleanup_trampoline
+	popq	%rsi
+
 	/* Zero EFLAGS */
 	pushq	$0
 	popfq
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 21d5cc1cd5fa..01d08d3e3e43 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -1,5 +1,6 @@
 #include <asm/processor.h>
 #include "pgtable.h"
+#include "../string.h"
 
 /*
  * __force_order is used by special_insns.h asm code to force instruction
@@ -18,6 +19,9 @@ struct paging_config {
 	unsigned long l5_required;
 };
 
+/* Buffer to preserve trampoline memory */
+static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
+
 /*
  * Trampoline address will be printed by extract_kernel() for debugging
  * purposes.
@@ -69,5 +73,14 @@ struct paging_config paging_prepare(void)
 
 	trampoline_32bit = (unsigned long *)paging_config.trampoline_start;
 
+	/* Preserve trampoline memory */
+	memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
+
 	return paging_config;
 }
+
+void cleanup_trampoline(void)
+{
+	/* Restore trampoline memory */
+	memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
+}
-- 
2.16.1