drm/amd/display: Reject gpio_bitshift >= 32 in bios_parser_get_gpio_pin_info()

[Why & How]
gpio_bitshift is a uint8_t read directly from the VBIOS GPIO pin table.
If the value is >= 32, the expression "1 << gpio_bitshift" triggers
undefined behaviour in C (shift count exceeds type width). On x86 the
shift is silently masked to 5 bits, producing an incorrect GPIO mask
that may cause wrong MMIO register bits to be toggled.

Validate gpio_bitshift before use and return BP_RESULT_BADBIOSTABLE for
out-of-range values.

Fixes: ae79c310b1a6 ("drm/amd/display: Add DCE12 bios parser support")
Assisted-by: Copilot:claude-opus-4.6
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit eadf438ab8d370b9d19acee9359918c85afeb80d)
Cc: stable@vger.kernel.org

diff --git a/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c b/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
index e8d8947c552ecf03d04c6247e5dc128836a1d2df..4f213ea865b8ad54ef6332e4a4512a424074f953 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
+++ b/drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
@@ -701,8 +701,10 @@ static enum bp_result bios_parser_get_gpio_pin_info(
                info->offset_en = info->offset + 1;
                info->offset_mask = info->offset - 1;
 
-               info->mask = (uint32_t) (1 <<
-                       header->gpio_pin[i].gpio_bitshift);
+               if (header->gpio_pin[i].gpio_bitshift >= 32)
+                       return BP_RESULT_BADBIOSTABLE;
+
+               info->mask = 1u << header->gpio_pin[i].gpio_bitshift;
                info->mask_y = info->mask + 2;
                info->mask_en = info->mask + 1;
                info->mask_mask = info->mask - 1;