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Commit 51c53180 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Greg Kroah-Hartman
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x86/boot/compressed/64: Do not read legacy ROM on EFI system 



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: 3548e131 ("x86/boot/compressed/64: Find a place for 32-bit trampoline")
Reported-by: default avatarPitam Mitra <pitamm@gmail.com>
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarBockjoo 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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent eab5ea25

arch/x86/boot/compressed/pgtable_64.c

+16 −3
Original line number Diff line number Diff line 
#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().

	 */



	/*

	 * 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;