From: "Michel Dänzer" <michel@daenzer.net>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
"Alex Deucher" <alexander.deucher@amd.com>,
"Christian König" <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
Subject: Re: [PATCH] drm/amd/display/dc/dce: Fix multiple potential integer overflows
Date: Wed, 4 Jul 2018 09:38:19 +0200 [thread overview]
Message-ID: <c663121e-1db8-9d7f-6b66-2c41e6a8bb70@daenzer.net> (raw)
In-Reply-To: <20180704011305.GA15742@embeddedor.com>
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
WARNING: multiple messages have this Message-ID (diff)
From: "Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>
To: "Gustavo A. R. Silva"
<gustavo-L1vi/lXTdts+Va1GwOuvDg@public.gmane.org>,
"Alex Deucher" <alexander.deucher-5C7GfCeVMHo@public.gmane.org>,
"Christian König" <christian.koenig-5C7GfCeVMHo@public.gmane.org>,
"David (ChunMing) Zhou"
<David1.Zhou-5C7GfCeVMHo@public.gmane.org>,
"David Airlie" <airlied-cv59FeDIM0c@public.gmane.org>
Cc: amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org,
dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] drm/amd/display/dc/dce: Fix multiple potential integer overflows
Date: Wed, 4 Jul 2018 09:38:19 +0200 [thread overview]
Message-ID: <c663121e-1db8-9d7f-6b66-2c41e6a8bb70@daenzer.net> (raw)
In-Reply-To: <20180704011305.GA15742-L1vi/lXTdts+Va1GwOuvDg@public.gmane.org>
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
_______________________________________________
amd-gfx mailing list
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next prev parent reply other threads:[~2018-07-04 7:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-04 1:13 [PATCH] drm/amd/display/dc/dce: Fix multiple potential integer overflows Gustavo A. R. Silva
2018-07-04 7:38 ` Michel Dänzer [this message]
2018-07-04 7:38 ` Michel Dänzer
2018-07-04 12:51 ` Gustavo A. R. Silva
2018-07-04 17:51 ` Harry Wentland
2018-07-04 17:51 ` Harry Wentland
2018-07-04 17:54 ` Gustavo A. R. Silva
2018-07-04 18:05 ` Harry Wentland
2018-07-04 18:05 ` Harry Wentland
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