[PATCH] ACPI: SPCR: check if table->serial_port.access_width is too wide

[Mark Langsdorf <mlangsdo@redhat.com>]

If table->serial_port.access_width is more than 29, it causes
undefined behavior when ACPI_ACCESS_BIT_WIDTH shifts it to
(1 << ((size) + 2)):

[    0.000000] UBSAN: Undefined behaviour in drivers/acpi/spcr.c:114:11
[    0.000000] shift exponent 102 is too large for 32-bit type 'int'

Test that serial_port.access_width is less than 30 and set it to 6
if it is not.

Signed-off-by: Mark Langsdorf <mlangsdo@redhat.com>
---
 drivers/acpi/spcr.c    |  8 ++++++--
 include/acpi/actypes.h | 10 ++++++++--
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index 134f7f60cf8102..52f17d631d24e9 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -111,8 +111,12 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
 		pr_info("SPCR table version %d\n", table->header.revision);
 
 	if (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
-		switch (ACPI_ACCESS_BIT_WIDTH((
-			table->serial_port.access_width))) {
+		u32 bit_width = table->serial_port.access_width;
+		if(bit_width > ACPI_ACCESS_BIT_MAX) {
+			pr_err("Unacceptable wide SPCR Access Width.  Defaulting to byte size\n");
+			bit_width = ACPI_ACCESS_BIT_DEFAULT;
+		}
+		switch (ACPI_ACCESS_BIT_WIDTH((bit_width))) {
 		default:
 			pr_err("Unexpected SPCR Access Width.  Defaulting to byte size\n");
 			fallthrough;
diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
index 92c71dfce0d5d9..cefbb7ad253e02 100644
--- a/include/acpi/actypes.h
+++ b/include/acpi/actypes.h
@@ -536,8 +536,14 @@ typedef u64 acpi_integer;
  * Can be used with access_width of struct acpi_generic_address and access_size of
  * struct acpi_resource_generic_register.
  */
-#define ACPI_ACCESS_BIT_WIDTH(size)     (1 << ((size) + 2))
-#define ACPI_ACCESS_BYTE_WIDTH(size)    (1 << ((size) - 1))
+#define ACPI_ACCESS_BIT_SHIFT		2
+#define ACPI_ACCESS_BYTE_SHIFT		-1
+#define ACPI_ACCESS_BIT_MAX		(31 - ACPI_ACCESS_BIT_SHIFT)
+#define ACPI_ACCESS_BYTE_MAX		(31 - ACPI_ACCESS_BYTE_SHIFT)
+#define ACPI_ACCESS_BIT_DEFAULT		(8 - ACPI_ACCESS_BIT_SHIFT)
+#define ACPI_ACCESS_BYTE_DEFAULT	(8 - ACPI_ACCESS_BYTE_SHIFT)
+#define ACPI_ACCESS_BIT_WIDTH(size)	(1 << ((size) + ACPI_ACCESS_BIT_SHIFT))
+#define ACPI_ACCESS_BYTE_WIDTH(size)	(1 << ((size) + ACPI_ACCESS_BYTE_SHIFT))
 
 /*******************************************************************************
  *
-- 
2.26.3