[04/11] ACPICA: Do not touch VGA memory when EBDA < 1ki_b
Commit Message
From: Vit Kabele <vit@kabele.me>
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@kabele.me>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/acpi/acpica/tbxfroot.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)
===================================================================
@@ -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) {