Re: [PATCH] drm/[radeon|amdgpu]: Replace one-element array and use struct_size() helper

[Alex Deucher <alexdeucher@gmail.com>]

On Fri, May 22, 2020 at 1:39 PM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
>
> The current codebase makes use of one-element arrays in the following
> form:
>
> struct something {
>     int length;
>     u8 data[1];
> };
>
> struct something *instance;
>
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
>
> but the preferred mechanism to declare variable-length types such as
> these ones is a flexible array member[1][2], introduced in C99:
>
> struct foo {
>         int stuff;
>         struct boo array[];
> };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on. So, replace
> the one-element array with a flexible-array member.
>
> Also, make use of the new struct_size() helper to properly calculate the
> size of struct SISLANDS_SMC_SWSTATE.
>
> This issue was found with the help of Coccinelle and, audited and fixed
> _manually_.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Applied.  Thanks!

Alex

> ---
>  drivers/gpu/drm/amd/amdgpu/si_dpm.c       | 5 ++---
>  drivers/gpu/drm/amd/amdgpu/sislands_smc.h | 2 +-
>  drivers/gpu/drm/radeon/si_dpm.c           | 5 ++---
>  3 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/si_dpm.c b/drivers/gpu/drm/amd/amdgpu/si_dpm.c
> index c00ba4b23c9a6..0fc56c5bac080 100644
> --- a/drivers/gpu/drm/amd/amdgpu/si_dpm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/si_dpm.c
> @@ -5715,10 +5715,9 @@ static int si_upload_sw_state(struct amdgpu_device *adev,
>         int ret;
>         u32 address = si_pi->state_table_start +
>                 offsetof(SISLANDS_SMC_STATETABLE, driverState);
> -       u32 state_size = sizeof(SISLANDS_SMC_SWSTATE) +
> -               ((new_state->performance_level_count - 1) *
> -                sizeof(SISLANDS_SMC_HW_PERFORMANCE_LEVEL));
>         SISLANDS_SMC_SWSTATE *smc_state = &si_pi->smc_statetable.driverState;
> +       size_t state_size = struct_size(smc_state, levels,
> +                                       new_state->performance_level_count);
>
>         memset(smc_state, 0, state_size);
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/sislands_smc.h b/drivers/gpu/drm/amd/amdgpu/sislands_smc.h
> index d2930eceaf3c8..a089dbf8f7a93 100644
> --- a/drivers/gpu/drm/amd/amdgpu/sislands_smc.h
> +++ b/drivers/gpu/drm/amd/amdgpu/sislands_smc.h
> @@ -186,7 +186,7 @@ struct SISLANDS_SMC_SWSTATE
>      uint8_t                             levelCount;
>      uint8_t                             padding2;
>      uint8_t                             padding3;
> -    SISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[1];
> +    SISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[];
>  };
>
>  typedef struct SISLANDS_SMC_SWSTATE SISLANDS_SMC_SWSTATE;
> diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
> index a167e1c36d243..bab01ca864c63 100644
> --- a/drivers/gpu/drm/radeon/si_dpm.c
> +++ b/drivers/gpu/drm/radeon/si_dpm.c
> @@ -5253,10 +5253,9 @@ static int si_upload_sw_state(struct radeon_device *rdev,
>         int ret;
>         u32 address = si_pi->state_table_start +
>                 offsetof(SISLANDS_SMC_STATETABLE, driverState);
> -       u32 state_size = sizeof(SISLANDS_SMC_SWSTATE) +
> -               ((new_state->performance_level_count - 1) *
> -                sizeof(SISLANDS_SMC_HW_PERFORMANCE_LEVEL));
>         SISLANDS_SMC_SWSTATE *smc_state = &si_pi->smc_statetable.driverState;
> +       size_t state_size = struct_size(smc_state, levels,
> +                                       new_state->performance_level_count);
>
>         memset(smc_state, 0, state_size);
>
> --
> 2.26.2
>
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