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

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[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: ae79c310b1 ("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 eadf438ab8)
Cc: stable@vger.kernel.org
This commit is contained in:
Harry Wentland 2026-05-05 11:50:07 -04:00 committed by Alex Deucher
parent da48bc4461
commit 49c3da6596
1 changed files with 4 additions and 2 deletions
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6
drivers/gpu/drm/amd/display/dc/bios/bios_parser2.c
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@ -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;