From: Vit Kabele <vit@xxxxxxxxx> 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: Vit Kabele <vit@xxxxxxxxx> Signed-off-by: Bob Moore <robert.moore@xxxxxxxxx> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> --- drivers/acpi/acpica/tbxfroot.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) Index: linux-pm/drivers/acpi/acpica/tbxfroot.c =================================================================== --- linux-pm.orig/drivers/acpi/acpica/tbxfroot.c +++ linux-pm/drivers/acpi/acpica/tbxfroot.c @@ -114,6 +114,7 @@ acpi_find_root_pointer(acpi_physical_add 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_add */ 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) {
