[tip:x86/mm] x86/boot/compressed/64: Save and restore trampoline memory

[tip-bot for Kirill A. Shutemov]

Commit-ID:  fb5268354d20b82c12569e325b0d051c09f983f7
Gitweb:     https://git.kernel.org/tip/fb5268354d20b82c12569e325b0d051c09f983f7
Author:     Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
AuthorDate: Mon, 26 Feb 2018 21:04:49 +0300
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 12 Mar 2018 09:37:25 +0100

x86/boot/compressed/64: Save and restore trampoline memory

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.

Tested-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/20180226180451.86788-4-kirill.shutemov@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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);
+}