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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Wed, 2 Nov 2022 12:12:16 -0400
Message-ID: <CADnq5_NVpsFJdHfizqRxidXqN5CZJ-nQpqfEA3Ngd3viojjBXA@mail.gmail.com>
Subject: Re: [PATCH v2] [next] drm/amdgpu: Replace one-element array with
 flexible-array member
To:     Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Cc:     Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Hans de Goede <hdegoede@redhat.com>,
        Claudio Suarez <cssk@net-c.es>,
        Harry Wentland <harry.wentland@amd.com>,
        Grigory Vasilyev <h0tc0d3@gmail.com>,
        Slark Xiao <slark_xiao@163.com>,
        Rongguang Wei <weirongguang@kylinos.cn>,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
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Applied.  Thanks!

Alex

On Fri, Oct 28, 2022 at 9:31 PM Paulo Miguel Almeida
<paulo.miguel.almeida.rodenas@gmail.com> wrote:
>
> One-element arrays are deprecated, and we are replacing them with
> flexible array members instead. So, replace one-element array with
> flexible-array member in struct _ATOM_FAKE_EDID_PATCH_RECORD and
> refactor the rest of the code accordingly.
>
> Important to mention is that doing a build before/after this patch
> results in no binary output differences.
>
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/238
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836 [1]
>
> Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
> ---
> Changelog:
>
> v2: no binary output differences patch; report binary changes findings
>     on commit log. Res: Kees Cook
> v1: https://lore.kernel.org/lkml/Y1tkWdwPUp+UdpM0@mail.google.com/
> ---
>  drivers/gpu/drm/amd/amdgpu/atombios_encoders.c | 7 +++++--
>  drivers/gpu/drm/amd/include/atombios.h         | 2 +-
>  2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
> index 6be9ac2b9c5b..18ae9433e463 100644
> --- a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
> +++ b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
> @@ -2081,8 +2081,11 @@ amdgpu_atombios_encoder_get_lcd_info(struct amdgpu_encoder *encoder)
>                                                 }
>                                         }
>                                         record += fake_edid_record->ucFakeEDIDLength ?
> -                                               fake_edid_record->ucFakeEDIDLength + 2 :
> -                                               sizeof(ATOM_FAKE_EDID_PATCH_RECORD);
> +                                                 struct_size(fake_edid_record,
> +                                                             ucFakeEDIDString,
> +                                                             fake_edid_record->ucFakeEDIDLength) :
> +                                                 /* empty fake edid record must be 3 bytes long */
> +                                                 sizeof(ATOM_FAKE_EDID_PATCH_RECORD) + 1;
>                                         break;
>                                 case LCD_PANEL_RESOLUTION_RECORD_TYPE:
>                                         panel_res_record = (ATOM_PANEL_RESOLUTION_PATCH_RECORD *)record;
> diff --git a/drivers/gpu/drm/amd/include/atombios.h b/drivers/gpu/drm/amd/include/atombios.h
> index 15943bc21bc5..b5b1d073f8e2 100644
> --- a/drivers/gpu/drm/amd/include/atombios.h
> +++ b/drivers/gpu/drm/amd/include/atombios.h
> @@ -4107,7 +4107,7 @@ typedef struct _ATOM_FAKE_EDID_PATCH_RECORD
>  {
>    UCHAR ucRecordType;
>    UCHAR ucFakeEDIDLength;       // = 128 means EDID length is 128 bytes, otherwise the EDID length = ucFakeEDIDLength*128
> -  UCHAR ucFakeEDIDString[1];    // This actually has ucFakeEdidLength elements.
> +  UCHAR ucFakeEDIDString[];     // This actually has ucFakeEdidLength elements.
>  } ATOM_FAKE_EDID_PATCH_RECORD;
>
>  typedef struct  _ATOM_PANEL_RESOLUTION_PATCH_RECORD
> --
> 2.37.3
>