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Commit 1b3a6264 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Thomas Gleixner
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x86/boot/compressed/64: Validate trampoline placement against E820 



There were two report of boot failure cased by trampoline placed into
a reserved memory region. It can happen on machines that don't report
EBDA correctly.

Fix the problem by re-validating the found address against the E820 table.
If the address is in a reserved area, find the next usable region below the
initial address.

Fixes: 3548e131 ("x86/boot/compressed/64: Find a place for 32-bit trampoline")
Reported-by: default avatarDmitry Malkin <d.malkin@real-time-systems.com>
Reported-by: default avataryouling 257 <youling257@gmail.com>
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180801133225.38121-1-kirill.shutemov@linux.intel.com
parent 6b470376

arch/x86/boot/compressed/pgtable_64.c

+55 −18
Original line number Diff line number Diff line 
#include <asm/e820/types.h>

#include <asm/processor.h>

#include "pgtable.h"

#include "../string.h"
@@ -34,10 +35,62 @@ unsigned long *trampoline_32bit __section(.data); 
extern struct boot_params *boot_params;

int cmdline_find_option_bool(const char *option);



static unsigned long find_trampoline_placement(void)

{

	unsigned long bios_start, ebda_start;

	unsigned long trampoline_start;

	struct boot_e820_entry *entry;

	int i;



	/*

	 * Find a suitable spot for the trampoline.

	 * This code is based on reserve_bios_regions().

	 */



	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;



	if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)

		bios_start = ebda_start;



	bios_start = round_down(bios_start, PAGE_SIZE);



	/* Find the first usable memory region under bios_start. */

	for (i = boot_params->e820_entries - 1; i >= 0; i--) {

		entry = &boot_params->e820_table[i];



		/* Skip all entries above bios_start. */

		if (bios_start <= entry->addr)

			continue;



		/* Skip non-RAM entries. */

		if (entry->type != E820_TYPE_RAM)

			continue;



		/* Adjust bios_start to the end of the entry if needed. */

		if (bios_start > entry->addr + entry->size)

			bios_start = entry->addr + entry->size;



		/* Keep bios_start page-aligned. */

		bios_start = round_down(bios_start, PAGE_SIZE);



		/* Skip the entry if it's too small. */

		if (bios_start - TRAMPOLINE_32BIT_SIZE < entry->addr)

			continue;



		break;

	}



	/* Place the trampoline just below the end of low memory */

	return bios_start - TRAMPOLINE_32BIT_SIZE;

}



struct paging_config paging_prepare(void *rmode)

{

	struct paging_config paging_config = {};

	unsigned long bios_start, ebda_start;



	/* Initialize boot_params. Required for cmdline_find_option_bool(). */

	boot_params = rmode;
@@ -61,23 +114,7 @@ struct paging_config paging_prepare(void *rmode) 
		paging_config.l5_required = 1;

	}



	/*

	 * Find a suitable spot for the trampoline.

	 * This code is based on reserve_bios_regions().

	 */



	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;



	if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)

		bios_start = ebda_start;



	/* Place the trampoline just below the end of low memory, aligned to 4k */

	paging_config.trampoline_start = bios_start - TRAMPOLINE_32BIT_SIZE;

	paging_config.trampoline_start = round_down(paging_config.trampoline_start, PAGE_SIZE);

	paging_config.trampoline_start = find_trampoline_placement();



	trampoline_32bit = (unsigned long *)paging_config.trampoline_start;