Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] drm/amd/display/dc/dce: Fix multiple potential integer
 overflows
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        "David (ChunMing) Zhou" <David1.Zhou@amd.com>,
        David Airlie <airlied@linux.ie>
Cc:     dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20180704011305.GA15742@embeddedor.com>
From:   =?UTF-8?Q?Michel_D=c3=a4nzer?= <michel@daenzer.net>
Openpgp: preference=signencrypt
Autocrypt: addr=michel@daenzer.net; prefer-encrypt=mutual; keydata=
 xsDiBDsehS8RBACbsIQEX31aYSIuEKxEnEX82ezMR8z3LG8ktv1KjyNErUX9Pt7AUC7W3W0b
 LUhu8Le8S2va6hi7GfSAifl0ih3k6Bv1Itzgnd+7ZmSrvCN8yGJaHNQfAevAuEboIb+MaVHo
 9EMJj4ikOcRZCmQWw7evu/D9uQdtkCnRY9iJiAGxbwCguBHtpoGMxDOINCr5UU6qt+m4O+UD
 /355ohBBzzyh49lTj0kTFKr0Ozd20G2FbcqHgfFL1dc1MPyigej2gLga2osu2QY0ObvAGkOu
 WBi3LTY8Zs8uqFGDC4ZAwMPoFy3yzu3ne6T7d/68rJil0QcdQjzzHi6ekqHuhst4a+/+D23h
 Za8MJBEcdOhRhsaDVGAJSFEQB1qLBACOs0xN+XblejO35gsDSVVk8s+FUUw3TSWJBfZa3Imp
 V2U2tBO4qck+wqbHNfdnU/crrsHahjzBjvk8Up7VoY8oT+z03sal2vXEonS279xN2B92Tttr
 AgwosujguFO/7tvzymWC76rDEwue8TsADE11ErjwaBTs8ZXfnN/uAANgPM0jTWljaGVsIERh
 ZW56ZXIgPG1pY2hlbEBkYWVuemVyLm5ldD7CXgQTEQIAHgUCQFXxJgIbAwYLCQgHAwIDFQID
 AxYCAQIeAQIXgAAKCRBaga+OatuyAIrPAJ9ykonXI3oQcX83N2qzCEStLNW47gCeLWm/QiPY
 jqtGUnnSbyuTQfIySkLOwE0EOx6FRRAEAJZkcvklPwJCgNiw37p0GShKmFGGqf/a3xZZEpjI
 qNxzshFRFneZze4f5LhzbX1/vIm5+ZXsEWympJfZzyCmYPw86QcFxyZflkAxHx9LeD+89Elx
 bw6wT0CcLvSv8ROfU1m8YhGbV6g2zWyLD0/naQGVb8e4FhVKGNY2EEbHgFBrAAMGA/0VktFO
 CxFBdzLQ17RCTwCJ3xpyP4qsLJH0yCoA26rH2zE2RzByhrTFTYZzbFEid3ddGiHOBEL+bO+2
 GNtfiYKmbTkj1tMZJ8L6huKONaVrASFzLvZa2dlc2zja9ZSksKmge5BOTKWgbyepEc5qxSju
 YsYrX5xfLgTZC5abhhztpcJGBBgRAgAGBQI7HoVFAAoJEFqBr45q27IAlscAn2Ufk2d6/3p4
 Cuyz/NX7KpL2dQ8WAJ9UD5JEakhfofed8PSqOM7jOO3LCA==
Message-ID: <c663121e-1db8-9d7f-6b66-2c41e6a8bb70@daenzer.net>
Date:   Wed, 4 Jul 2018 09:38:19 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.8.0
MIME-Version: 1.0
In-Reply-To: <20180704011305.GA15742@embeddedor.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-CA
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2018-07-04 03:13 AM, Gustavo A. R. Silva wrote:
> Add suffix ULL to constant 5 and cast variables target_pix_clk_khz and
> feedback_divider to uint64_t in order to avoid multiple potential integer
> overflows and give the compiler complete information about the proper
> arithmetic to use.
> 
> Notice that such constant and variables are used in contexts that
> expect expressions of type uint64_t (64 bits, unsigned). The current
> casts to uint64_t effectively apply to each expression as a whole,
> but they do not prevent them from being evaluated using 32-bit
> arithmetic instead of 64-bit arithmetic.
> 
> Also, once the expressions are properly evaluated using 64-bit
> arithmentic, there is no need for the parentheses that enclose
> them.
> 
> Addresses-Coverity-ID: 1460245 ("Unintentional integer overflow")
> Addresses-Coverity-ID: 1460286 ("Unintentional integer overflow")
> Addresses-Coverity-ID: 1460401 ("Unintentional integer overflow")
> Fixes: 4562236b3bc0 ("drm/amd/dc: Add dc display driver (v2)")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> 
> [...]
>  
> @@ -145,8 +145,8 @@ static bool calculate_fb_and_fractional_fb_divider(
>   * of fractional feedback decimal point and the fractional FB Divider precision
>   * is 2 then the equation becomes (ullfeedbackDivider + 5*100) / (10*100))*/
>  
> -	feedback_divider += (uint64_t)
> -			(5 * calc_pll_cs->fract_fb_divider_precision_factor);
> +	feedback_divider += 5UL *
> +			    calc_pll_cs->fract_fb_divider_precision_factor;

This should be 5ULL, as the commit log says, otherwise it's still only
32 bits on 32-bit platforms.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer