linux-hardening - Re: [PATCH] [next] drm/amdgpu: Replace one-element array with flexible-array member

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Date:   Fri, 28 Oct 2022 09:18:39 +0200
From:   Christian König <christian.koenig@....com>
To:     Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Hans de Goede <hdegoede@...hat.com>,
        Grigory Vasilyev <h0tc0d3@...il.com>,
        Claudio Suarez <cssk@...-c.es>,
        Slark Xiao <slark_xiao@....com>,
        Rongguang Wei <weirongguang@...inos.cn>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] [next] drm/amdgpu: Replace one-element array with
 flexible-array member

Am 28.10.22 um 07:10 schrieb Paulo Miguel Almeida:
> 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.
>
> 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]

I'm not sure if that's a good idea. We had multiple attempts to refactor 
this now and it always caused a regression.

Additional to that the header in question came from our BIOS team and 
isn't following Linux styles in general.

Alex what do you think?

Regards,
Christian.

>
> Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/atombios_encoders.c | 10 +++++++---
>   drivers/gpu/drm/amd/include/atombios.h         |  2 +-
>   2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
> index 6be9ac2b9c5b..6b5abf1249db 100644
> --- a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
> +++ b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
> @@ -2079,10 +2079,14 @@ amdgpu_atombios_encoder_get_lcd_info(struct amdgpu_encoder *encoder)
>   							} else
>   								kfree(edid);
>   						}
> +
> +						record += struct_size(fake_edid_record,
> +								      ucFakeEDIDString,
> +								      fake_edid_record->ucFakeEDIDLength);
> +					} else {
> +						/* empty fake edid record must be 3 bytes long */
> +						record += sizeof(ATOM_FAKE_EDID_PATCH_RECORD) + 1;
>   					}
> -					record += fake_edid_record->ucFakeEDIDLength ?
> -						fake_edid_record->ucFakeEDIDLength + 2 :
> -						sizeof(ATOM_FAKE_EDID_PATCH_RECORD);
>   					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