[PATCH 4.20 61/76] x86/boot/compressed/64: Do not read legacy ROM on EFI system

Greg Kroah-Hartman
2019-03-08T13:05:30Z

From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

commit 6f913de3231e1d70a871135b38219da7810df218 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- 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

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_pla
* 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;