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Subject[tip:x86/mm] x86/boot/compressed/64: Save and restore trampoline memory
Commit-ID:  fb5268354d20b82c12569e325b0d051c09f983f7
Gitweb: https://git.kernel.org/tip/fb5268354d20b82c12569e325b0d051c09f983f7
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
AuthorDate: Mon, 26 Feb 2018 21:04:49 +0300
Committer: Ingo Molnar <mingo@kernel.org>
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@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/20180226180451.86788-4-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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);
+}
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