Re: [PATCH] drm/amd/ras: Fix type size of remainder argument

[Kees Cook <kees@kernel.org>]

On Tue, Feb 24, 2026 at 05:43:18PM -0800, Kees Cook wrote:
> Forcing an int to be dereferenced at uint64_t for div64_u64_rem() runs
> the risk of endian confusion and stack overflowing writes. Seen while
> preparing to enable -Warray-bounds globally:
> 
> In file included from ../arch/x86/include/asm/processor.h:35,
>                  from ../include/linux/sched.h:13,
>                  from ../include/linux/ratelimit.h:6,
>                  from ../include/linux/dev_printk.h:16,
>                  from ../drivers/gpu/drm/amd/amdgpu/../ras/ras_mgr/ras_sys.h:29,
>                  from ../drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras.h:27,
>                  from ../drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c:24:
> In function 'div64_u64_rem',
>     inlined from 'ras_core_convert_timestamp_to_time' at ../drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c:72:9:
> ../include/linux/math64.h:56:20: error: array subscript 'u64 {aka long long unsigned int}[0]' is partly outside array bounds of 'int[1]' [-Werror=array-bounds=]
>    56 |         *remainder = dividend % divisor;
>       |         ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
> ../drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c: In function 'ras_core_convert_timestamp_to_time':
> ../drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c:70:19: note: object 'remaining_seconds' of size 4
>    70 |         int days, remaining_seconds;
>       |                   ^~~~~~~~~~~~~~~~~
> 
> Switch remaining_seconds to uint64_t to avoid the problems.
> 
> Fixes: ace232eff50e ("drm/amdgpu: Add ras module files into amdgpu")
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: YiPeng Chai <YiPeng.Chai@amd.com>
> Cc: Tao Zhou <tao.zhou1@amd.com>
> Cc: Hawking Zhang <Hawking.Zhang@amd.com>
> Cc: <amd-gfx@lists.freedesktop.org>
> Cc: <dri-devel@lists.freedesktop.org>
> ---
>  drivers/gpu/drm/amd/ras/rascore/ras_core.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/ras/rascore/ras_core.c b/drivers/gpu/drm/amd/ras/rascore/ras_core.c
> index 01122b55c98a..91e16b0b98f9 100644
> --- a/drivers/gpu/drm/amd/ras/rascore/ras_core.c
> +++ b/drivers/gpu/drm/amd/ras/rascore/ras_core.c
> @@ -63,13 +63,14 @@ int ras_core_convert_timestamp_to_time(struct ras_core_context *ras_core,
>  {
>  	int days_in_month[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
>  	uint64_t month = 0, day = 0, hour = 0, minute = 0, second = 0;
> +	uint64_t remaining_seconds;
>  	uint32_t year = 0;
>  	int seconds_per_day = 24 * 60 * 60;
>  	int seconds_per_hour = 60 * 60;
>  	int seconds_per_minute = 60;
> -	int days, remaining_seconds;
> +	int days;
>  
> -	days = div64_u64_rem(timestamp, seconds_per_day, (uint64_t *)&remaining_seconds);
> +	days = div64_u64_rem(timestamp, seconds_per_day, &remaining_seconds);
>  
>  	/* utc_timestamp follows the Unix epoch */
>  	year = 1970;

Hm, 0day noticed this creates a problem on 32-bit systems:
https://lore.kernel.org/all/202602251312.pq8yvrww-lkp@intel.com

>  ld: drivers/gpu/drm/amd/ras/rascore/ras_core.o: in function `ras_core_convert_timestamp_to_time':
>  drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c:99:(.text+0x23e): undefined reference to `__udivmoddi4'
>  ld: drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c:100:(.text+0x253): undefined reference to `__udivdi3'
>  ld: drivers/gpu/drm/amd/amdgpu/../ras/rascore/ras_core.c:101:(.text+0x265): undefined reference to `__umoddi3'

I will investigate and send a v2...

-- 
Kees Cook