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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: 3548e131ec ("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
This commit is contained in:
Kirill A. Shutemov 2019-02-19 10:52:24 +03:00 committed by Thomas Gleixner
parent f9d230e893
commit 6f913de323
1 changed files with 16 additions and 3 deletions
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19
arch/x86/boot/compressed/pgtable_64.c
View File

@ -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;