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Mon, 8 Feb 2021 12:14:55 +0000 Subject: Re: [PATCH] drm/amdgpu: fix potential integer overflow on shift of a int To: Walter Harms , Colin King , Alex Deucher , David Airlie , Daniel Vetter , Huang Rui , Junwei Zhang , "amd-gfx@lists.freedesktop.org" , "dri-devel@lists.freedesktop.org" Cc: "kernel-janitors@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20210207230751.8576-1-colin.king@canonical.com> <3aed86cfb8014badbcbc4ee9f007976d@bfs.de> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <877bdf13-08d3-b471-40fb-02941cce3e4e@amd.com> Date: Mon, 8 Feb 2021 13:14:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <3aed86cfb8014badbcbc4ee9f007976d@bfs.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [2a02:908:1252:fb60:be8a:bd56:1f94:86e7] X-ClientProxiedBy: AM4PR05CA0028.eurprd05.prod.outlook.com (2603:10a6:205::41) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:be8a:bd56:1f94:86e7] (2a02:908:1252:fb60:be8a:bd56:1f94:86e7) by AM4PR05CA0028.eurprd05.prod.outlook.com (2603:10a6:205::41) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3825.20 via Frontend Transport; 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Only the fragment handling can't do more than 2GB at the same time. Christian. Am 08.02.21 um 12:05 schrieb Walter Harms: > i am curious: > what is the win to have a unsigned 64 bit integer in the first > place ? > > re, > wh > ________________________________________ > Von: Christian König > Gesendet: Montag, 8. Februar 2021 10:17:42 > An: Colin King; Alex Deucher; David Airlie; Daniel Vetter; Huang Rui; Junwei Zhang; amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org > Cc: kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org > Betreff: Re: [PATCH] drm/amdgpu: fix potential integer overflow on shift of a int > > Am 08.02.21 um 00:07 schrieb Colin King: >> From: Colin Ian King >> >> The left shift of int 32 bit integer constant 1 is evaluated using 32 >> bit arithmetic and then assigned to an unsigned 64 bit integer. In the >> case where *frag is 32 or more this can lead to an oveflow. Avoid this >> by shifting 1ULL. > Well that can't happen. Take a look at the code in that function: > >> max_frag = 31; > ... >> if (*frag >= max_frag) { >> *frag = max_frag; >> *frag_end = end & ~((1ULL << max_frag) - 1); >> } else { >> *frag_end = start + (1 << *frag); >> } > But I'm fine with applying the patch if it silences your warning. > > Regards, > Christian. > >> Addresses-Coverity: ("Unintentional integer overflow") >> Fixes: dfcd99f6273e ("drm/amdgpu: meld together VM fragment and huge page handling") >> Signed-off-by: Colin Ian King >> --- >> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c >> index 9d19078246c8..53a925600510 100644 >> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c >> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c >> @@ -1412,7 +1412,7 @@ static void amdgpu_vm_fragment(struct amdgpu_vm_update_params *params, >> *frag = max_frag; >> *frag_end = end & ~((1ULL << max_frag) - 1); >> } else { >> - *frag_end = start + (1 << *frag); >> + *frag_end = start + (1ULL << *frag); >> } >> } >>