Commit 8ff29065 authored by Vit Kabele's avatar Vit Kabele Committed by Rafael J. Wysocki
Browse files

ACPICA: Do not touch VGA memory when EBDA < 1ki_b 

ACPICA commit a36eda9631e84f271319c41288889dd5b1329369

The ACPICA code assumes that EBDA region must be at least 1ki_b in size.
Because this is not guaranteed, it might happen that while scanning the
memory for RSDP pointer, the kernel touches memory above 640ki_b.

This is unwanted as the VGA memory range may not be decoded or
even present when running under virtualization.

Link: https://github.com/acpica/acpica/commit/a36eda96


Signed-off-by: default avatarVit Kabele <vit@kabele.me>
Signed-off-by: default avatarBob Moore <robert.moore@intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 4fe54f50

drivers/acpi/acpica/tbxfroot.c

+15 −7
Original line number Diff line number Diff line
@@ -114,6 +114,7 @@ acpi_find_root_pointer(acpi_physical_address *table_address) 
	u8 *table_ptr;

	u8 *mem_rover;

	u32 physical_address;

	u32 ebda_window_size;



	ACPI_FUNCTION_TRACE(acpi_find_root_pointer);
@@ -145,24 +146,31 @@ acpi_find_root_pointer(acpi_physical_address *table_address) 
	 */

	if (physical_address > 0x400 && physical_address < 0xA0000) {

		/*

		 * 1b) Search EBDA paragraphs (EBDA is required to be a

		 *     minimum of 1K length)

		 * Calculate the scan window size

		 * The EBDA is not guaranteed to be larger than a ki_b and in case

		 * that it is smaller, the scanning function would leave the low

		 * memory and continue to the VGA range.

		 */

		ebda_window_size = ACPI_MIN(ACPI_EBDA_WINDOW_SIZE,

					    0xA0000 - physical_address);



		/*

		 * 1b) Search EBDA paragraphs

		 */

		table_ptr = acpi_os_map_memory((acpi_physical_address)

					       physical_address,

					       ACPI_EBDA_WINDOW_SIZE);

					       ebda_window_size);

		if (!table_ptr) {

			ACPI_ERROR((AE_INFO,

				    "Could not map memory at 0x%8.8X for length %u",

				    physical_address, ACPI_EBDA_WINDOW_SIZE));

				    physical_address, ebda_window_size));



			return_ACPI_STATUS(AE_NO_MEMORY);

		}



		mem_rover =

		    acpi_tb_scan_memory_for_rsdp(table_ptr,

						 ACPI_EBDA_WINDOW_SIZE);

		acpi_os_unmap_memory(table_ptr, ACPI_EBDA_WINDOW_SIZE);

		    acpi_tb_scan_memory_for_rsdp(table_ptr, ebda_window_size);

		acpi_os_unmap_memory(table_ptr, ebda_window_size);



		if (mem_rover) {