Re: [PATCH 2/2] drm/amdgpu: Fix type of second parameter in odn_edit_dpm_table() callback

Kees Cook
2022-11-02T15:43:01Z

On Wed, Nov 02, 2022 at 08:25:40AM -0700, Nathan Chancellor wrote:
> With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
> indirect call targets are validated against the expected function
> pointer prototype to make sure the call target is valid to help mitigate
> ROP attacks. If they are not identical, there is a failure at run time,
> which manifests as either a kernel panic or thread getting killed. A
> proposed warning in clang aims to catch these at compile time, which
> reveals:
>
> drivers/gpu/drm/amd/amdgpu/../pm/swsmu/amdgpu_smu.c:3008:29: error: incompatible function pointer types initializing 'int (*)(void *, uint32_t, long *, uint32_t)' (aka 'int (*)(void *, unsigned int, long *, unsigned int)') with an expression of type 'int (void *, enum PP_OD_DPM_TABLE_COMMAND, long *, uint32_t)' (aka 'int (void *, enum PP_OD_DPM_TABLE_COMMAND, long *, unsigned int)') [-Werror,-Wincompatible-function-pointer-types-strict]
> .odn_edit_dpm_table = smu_od_edit_dpm_table,
> ^~~~~~~~~~~~~~~~~~~~~
> 1 error generated.
>
> There are only two implementations of ->odn_edit_dpm_table() in 'struct
> amd_pm_funcs': smu_od_edit_dpm_table() and pp_odn_edit_dpm_table(). One
> has a second parameter type of 'enum PP_OD_DPM_TABLE_COMMAND' and the
> other uses 'u32'. Ultimately, smu_od_edit_dpm_table() calls
> ->od_edit_dpm_table() from 'struct pptable_funcs' and
> pp_odn_edit_dpm_table() calls ->odn_edit_dpm_table() from 'struct
> pp_hwmgr_func', which both have a second parameter type of 'enum
> PP_OD_DPM_TABLE_COMMAND'.
>
> Update the type parameter in both the prototype in 'struct amd_pm_funcs'
> and pp_odn_edit_dpm_table() to 'enum PP_OD_DPM_TABLE_COMMAND', which
> cleans up the warning.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Reported-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

--
Kees Cook