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charset="us-ascii" Content-ID: MIME-Version: 1.0 X-OriginatorOrg: meta.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 83ccfb87-2477-460d-1bba-08dab11a2f49 X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Oct 2022 15:05:24.5849 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 7ERTVdNY+NETsx+DIAyNpT8pMUDwO0A5zG82gW7ckk4eCazZ6hc6zHzmHjPJ5qaLyZ7gPxCzlEp18xWqtYm/4A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR15MB3660 X-Proofpoint-ORIG-GUID: JPFabpDUaReEATIMZbqAL49GjivK6_Cr X-Proofpoint-GUID: JPFabpDUaReEATIMZbqAL49GjivK6_Cr X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-10-18_04,2022-10-18_01,2022-06-22_01 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Oct 18, 2022, at 7:50 AM, Christoph Hellwig wrote: > > On Mon, Oct 17, 2022 at 04:23:52PM +0000, Song Liu wrote: >>> Well, nothing explains what the method is to avoid having memory >>> that is mapped writable and executable at the same time, which really >>> could use some explanation here (and in the main patch as well). >> >> Thanks for the feedback. I will add this. >> >> Does the code look good to you? I personally think patch 1, 2, 4 could >> ship with a little more work. > > I only took a quick look and I'm not sure how the W^X actually works. > Yes, it alls into the text poke helpers, but how do these work on > less than page sized allocations? Aha, I guess I understand your point (and concern) now. It is the same as text poke into static kernel text: we create a local writable mapping to the memory we need to update. For less than page sized allocation, this mapping does have access to X memory that may belong to a different allocation, just like text poke into static kernel text. Maybe we need something like vcopy_exec(x_mem, tmp_buf, size), where we explicitly check the allowed memory of x_mem is bigger or equal to size. And users of vmalloc_exec should only use vcopy_exec to update memory from vmalloc_exec. Does this make sense? Did I understand your concern correctly? Thanks, Song