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=?utf-8?B?eDNiVHlzRXIxSC9uUjBJUWN2NGpwL1lmdFV2bzdGK0ZrOFRsYzRHa3BLc0Rm?= =?utf-8?B?aGdkOUFZazh2RG12UnZ2ZDRQUHM3elg4aDIwUWZXdFdObGNrekVMLzJsU0py?= =?utf-8?B?dFZIU2FkRXFQbXpmcSt4bmFXLzZMaHUrOC8yQ3BOaVlDaCt1Q2swRFRCT1BM?= =?utf-8?B?WFUrR2VaME5XM0g2WTlMV0xkSUpNRHZSZXhRTmdqNHhKcGdRLytPSXA4SGFE?= =?utf-8?B?aXFtbVc1WlNCRm9lOGh5Y1YvSDJiRllqN0djbDBNY1dRQXJ4UUd5YWk3UnU5?= =?utf-8?Q?zuIzEB1b?= X-OriginatorOrg: citrix.com X-MS-Exchange-CrossTenant-Network-Message-Id: a7b63c5a-45c0-44cf-c1b2-08db2b02d2e3 X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Mar 2023 18:25:33.4877 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Vbj1p8X+3EDWJoIU1bOtbLg7lnI0TXaphyXY6TzqsHw5Dz19wHs5EhWa5Em7yOmMci9td/PCPOe4JltEwSb7aR1uMT7Qtje5EnUTtZyh9Yo= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR03MB6020 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/03/2023 2:22 am, Li, Xin3 wrote: >> If there is no other concrete reason other than overflowing for assigning NMI and >> #DB with a stack level > 0, #VE should also be assigned with a stack level > 0, and >> #BP too. #VE can happen anytime and anywhere, so it is subject to overflowing too. > With IDT, both #VE and #BP do not use IST, but NMI, #DB, #MC and #DF do. > > Let's keep this "secret" logic for now, i.e., not change the stack levels > for #VE and #BP at this point. We can do "optimization", i.e., change them > later :). Fun fact.  #BP used to be IST, and used to share the same IST as #DF. This was spoiled by CVE-2018-8897 and a MovSS-delayed breakpoint over INT3, at which point hardware queued both a #BP and #DB on the same IST stack and lost program state. There's no need specific need for #BP to be IST to begin with, hence why making it not-IST was the security fix. ~Andrew