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Commit 93a209aa authored by Chao Fan's avatar Chao Fan Committed by Borislav Petkov
Browse files

x86/boot: Search for RSDP in memory 



Scan memory (EBDA) for the RSDP and verify RSDP by signature and
checksum.

 [ bp:
   - Trim commit message.
   - Simplify bios_get_rsdp_addr() and cleanup mad casting.
 ]

Signed-off-by: default avatarChao Fan <fanc.fnst@cn.fujitsu.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Cc: bhe@redhat.com
Cc: caoj.fnst@cn.fujitsu.com
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: indou.takao@jp.fujitsu.com
Cc: Ingo Molnar <mingo@redhat.com>
Cc: kasong@redhat.com
Cc: Kees Cook <keescook@chromium.org>
Cc: msys.mizuma@gmail.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190123110850.12433-5-fanc.fnst@cn.fujitsu.com
parent 33f0df8d

arch/x86/boot/compressed/acpi.c

+77 −0
Original line number Diff line number Diff line
@@ -107,3 +107,80 @@ static acpi_physical_address efi_get_rsdp_addr(void) 
#endif

	return rsdp_addr;

}



static u8 compute_checksum(u8 *buffer, u32 length)

{

	u8 *end = buffer + length;

	u8 sum = 0;



	while (buffer < end)

		sum += *(buffer++);



	return sum;

}



/* Search a block of memory for the RSDP signature. */

static u8 *scan_mem_for_rsdp(u8 *start, u32 length)

{

	struct acpi_table_rsdp *rsdp;

	u8 *address, *end;



	end = start + length;



	/* Search from given start address for the requested length */

	for (address = start; address < end; address += ACPI_RSDP_SCAN_STEP) {

		/*

		 * Both RSDP signature and checksum must be correct.

		 * Note: Sometimes there exists more than one RSDP in memory;

		 * the valid RSDP has a valid checksum, all others have an

		 * invalid checksum.

		 */

		rsdp = (struct acpi_table_rsdp *)address;



		/* BAD Signature */

		if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature))

			continue;



		/* Check the standard checksum */

		if (compute_checksum((u8 *)rsdp, ACPI_RSDP_CHECKSUM_LENGTH))

			continue;



		/* Check extended checksum if table version >= 2 */

		if ((rsdp->revision >= 2) &&

		    (compute_checksum((u8 *)rsdp, ACPI_RSDP_XCHECKSUM_LENGTH)))

			continue;



		/* Signature and checksum valid, we have found a real RSDP */

		return address;

	}

	return NULL;

}



/* Search RSDP address in EBDA. */

static acpi_physical_address bios_get_rsdp_addr(void)

{

	unsigned long address;

	u8 *rsdp;



	/* Get the location of the Extended BIOS Data Area (EBDA) */

	address = *(u16 *)ACPI_EBDA_PTR_LOCATION;

	address <<= 4;



	/*

	 * Search EBDA paragraphs (EBDA is required to be a minimum of

	 * 1K length)

	 */

	if (address > 0x400) {

		rsdp = scan_mem_for_rsdp((u8 *)address, ACPI_EBDA_WINDOW_SIZE);

		if (rsdp)

			return (acpi_physical_address)(unsigned long)rsdp;

	}



	/* Search upper memory: 16-byte boundaries in E0000h-FFFFFh */

	rsdp = scan_mem_for_rsdp((u8 *) ACPI_HI_RSDP_WINDOW_BASE,

					ACPI_HI_RSDP_WINDOW_SIZE);

	if (rsdp)

		return (acpi_physical_address)(unsigned long)rsdp;



	return 0;

}