[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'

Use the new ACPI_ACCESS_ defines to 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 | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index 25c2d0be953e..d589543875b8 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -107,8 +107,13 @@ 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;
-- 
2.26.3