[PATCH] x86/boot/compressed/64: Do not read legacy ROM on EFI system

[PATCH] x86/boot/compressed/64: Do not read legacy ROM on EFI system

[Kirill A. Shutemov]

EFI systems may not provide legacy ROM. The memory may not be mapped
at all.

Trying to dereference values in legacy ROM leads to crash on Macbook
Pro.

Only look for values in the legacy ROM for non-EFI system.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202351
Fixes: 3548e131ec6a ("x86/boot/compressed/64: Find a place for 32-bit trampoline")
Reported-by: Pitam Mitra <pitamm@gmail.com>
Tested-by: Bockjoo Kim <bockjoo@phys.ufl.edu>
---
 arch/x86/boot/compressed/pgtable_64.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 9e2157371491..f8debf7aeb4c 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -1,5 +1,7 @@
+#include <linux/efi.h>
 #include <asm/e820/types.h>
 #include <asm/processor.h>
+#include <asm/efi.h>
 #include "pgtable.h"
 #include "../string.h"
 
@@ -37,9 +39,10 @@ int cmdline_find_option_bool(const char *option);
 
 static unsigned long find_trampoline_placement(void)
 {
-	unsigned long bios_start, ebda_start;
+	unsigned long bios_start = 0, ebda_start = 0;
 	unsigned long trampoline_start;
 	struct boot_e820_entry *entry;
+	char *signature;
 	int i;
 
 	/*
@@ -47,8 +50,18 @@ static unsigned long find_trampoline_placement(void)
 	 * This code is based on reserve_bios_regions().
 	 */
 
-	ebda_start = *(unsigned short *)0x40e << 4;
-	bios_start = *(unsigned short *)0x413 << 10;
+	/*
+	 * EFI systems may not provide legacy ROM. The memory may not be mapped
+	 * at all.
+	 *
+	 * Only look for values in the legacy ROM for non-EFI system.
+	 */
+	signature = (char *)&boot_params->efi_info.efi_loader_signature;
+	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
+	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4)) {
+		ebda_start = *(unsigned short *)0x40e << 4;
+		bios_start = *(unsigned short *)0x413 << 10;
+	}
 
 	if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
 		bios_start = BIOS_START_MAX;
-- 
2.20.1

[tip:x86/boot] x86/boot/compressed/64: Do not read legacy ROM on EFI system

[tip-bot for Kirill A. Shutemov]

Commit-ID:  6f913de3231e1d70a871135b38219da7810df218
Gitweb:     https://git.kernel.org/tip/6f913de3231e1d70a871135b38219da7810df218
Author:     Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
AuthorDate: Tue, 19 Feb 2019 10:52:24 +0300
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 28 Feb 2019 12:25:05 +0100

x86/boot/compressed/64: Do not read legacy ROM on EFI system

EFI systems do not necessarily provide a legacy ROM. If the ROM is missing
the memory is not mapped at all.

Trying to dereference values in the legacy ROM area leads to a crash on
Macbook Pro.

Only look for values in the legacy ROM area for non-EFI system.

Fixes: 3548e131ec6a ("x86/boot/compressed/64: Find a place for 32-bit trampoline")
Reported-by: Pitam Mitra <pitamm@gmail.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Bockjoo Kim <bockjoo@phys.ufl.edu>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20190219075224.35058-1-kirill.shutemov@linux.intel.com
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202351

---
 arch/x86/boot/compressed/pgtable_64.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 9e2157371491..f8debf7aeb4c 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -1,5 +1,7 @@
+#include <linux/efi.h>
 #include <asm/e820/types.h>
 #include <asm/processor.h>
+#include <asm/efi.h>
 #include "pgtable.h"
 #include "../string.h"
 
@@ -37,9 +39,10 @@ int cmdline_find_option_bool(const char *option);
 
 static unsigned long find_trampoline_placement(void)
 {
-	unsigned long bios_start, ebda_start;
+	unsigned long bios_start = 0, ebda_start = 0;
 	unsigned long trampoline_start;
 	struct boot_e820_entry *entry;
+	char *signature;
 	int i;
 
 	/*
@@ -47,8 +50,18 @@ static unsigned long find_trampoline_placement(void)
 	 * This code is based on reserve_bios_regions().
 	 */
 
-	ebda_start = *(unsigned short *)0x40e << 4;
-	bios_start = *(unsigned short *)0x413 << 10;
+	/*
+	 * EFI systems may not provide legacy ROM. The memory may not be mapped
+	 * at all.
+	 *
+	 * Only look for values in the legacy ROM for non-EFI system.
+	 */
+	signature = (char *)&boot_params->efi_info.efi_loader_signature;
+	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
+	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4)) {
+		ebda_start = *(unsigned short *)0x40e << 4;
+		bios_start = *(unsigned short *)0x413 << 10;
+	}
 
 	if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
 		bios_start = BIOS_START_MAX;