linux-kernel - Re: [PATCH 2/2] drm/amdgpu: Fix type of second parameter in odn_edit_dpm

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Date:   Wed, 2 Nov 2022 08:42:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Sami Tolvanen <samitolvanen@...gle.com>, llvm@...ts.linux.dev,
        patches@...ts.linux.dev
Subject: Re: [PATCH 2/2] drm/amdgpu: Fix type of second parameter in
 odn_edit_dpm_table() callback

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@...gle.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

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

-- 
Kees Cook