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[2003:fa:af26:200:51a:ef03:a698:a1fc]) by smtp.gmail.com with ESMTPSA id af79cd13be357-910bc9363fcsm1969936185a.27.2026.05.19.14.08.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 May 2026 14:08:44 -0700 (PDT) Message-ID: <36f1c4f7-d3aa-4fa4-a9cf-93b4685535a6@grsecurity.net> Date: Tue, 19 May 2026 23:08:41 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] x86/cpufeatures: Make X86_FEATURE_SHSTK clearcpuid-able To: Borislav Petkov Cc: Thomas Gleixner , Ingo Molnar , Dave Hansen , Rick Edgecombe , x86@kernel.org, Peter Zijlstra , linux-kernel@vger.kernel.org References: <20260514160932.91556-1-minipli@grsecurity.net> <20260514165922.GGagX_amNCc0mZcz4d@fat_crate.local> <20260516152714.GBagiM0u1QN-6QAjUX@fat_crate.local> Content-Language: en-US, de-DE From: Mathias Krause Autocrypt: addr=minipli@grsecurity.net; keydata= xsDNBF4u6F8BDAC1kCIyATzlCiDBMrbHoxLywJSUJT9pTbH9MIQIUW8K1m2Ney7a0MTKWQXp 64/YTQNzekOmta1eZFQ3jqv+iSzfPR/xrDrOKSPrw710nVLC8WL993DrCfG9tm4z3faBPHjp zfXBIOuVxObXqhFGvH12vUAAgbPvCp9wwynS1QD6RNUNjnnAxh3SNMxLJbMofyyq5bWK/FVX 897HLrg9bs12d9b48DkzAQYxcRUNfL9VZlKq1fRbMY9jAhXTV6lcgKxGEJAVqXqOxN8DgZdU aj7sMH8GKf3zqYLDvndTDgqqmQe/RF/hAYO+pg7yY1UXpXRlVWcWP7swp8OnfwcJ+PiuNc7E gyK2QEY3z5luqFfyQ7308bsawvQcFjiwg+0aPgWawJ422WG8bILV5ylC8y6xqYUeSKv/KTM1 4zq2vq3Wow63Cd/qyWo6S4IVaEdfdGKVkUFn6FihJD/GxnDJkYJThwBYJpFAqJLj7FtDEiFz LXAkv0VBedKwHeBaOAVH6QEAEQEAAc0nTWF0aGlhcyBLcmF1c2UgPG1pbmlwbGlAZ3JzZWN1 cml0eS5uZXQ+wsERBBMBCgA7AhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAFiEEd7J359B9 wKgGsB94J4hPxYYBGYYFAmBbH/cCGQEACgkQJ4hPxYYBGYaX/gv/WYhaehD88XjpEO+yC6x7 bNWQbk7ea+m82fU2x/x6A9L4DN/BXIxqlONzk3ehvW3wt1hcHeF43q1M/z6IthtxSRi059RO SarzX3xfXC1pc5YMgCozgE0VRkxH4KXcijLyFFjanXe0HzlnmpIJB6zTT2jgI70q0FvbRpgc rs3VKSFb+yud17KSSN/ir1W2LZPK6er6actK03L92A+jaw+F8fJ9kJZfhWDbXNtEE0+94bMa cdDWTaZfy6XJviO3ymVe3vBnSDakVE0HwLyIKvfAEok+YzuSYm1Nbd2T0UxgSUZHYlrUUH0y tVxjEFyA+iJRSdm0rbAvzpwau5FOgxRQDa9GXH6ie6/ke2EuZc3STNS6EBciJm1qJ7xb2DTf SNyOiWdvop+eQZoznJJte931pxkRaGwV+JXDM10jGTfyV7KT9751xdn6b6QjQANTgNnGP3qs TO5oU3KukRHgDcivzp6CWb0X/WtKy0Y/54bTJvI0e5KsAz/0iwH19IB0vpYLzsDNBF4u6F8B DADwcu4TPgD5aRHLuyGtNUdhP9fqhXxUBA7MMeQIY1kLYshkleBpuOpgTO/ikkQiFdg13yIv q69q/feicsjaveIEe7hUI9lbWcB9HKgVXW3SCLXBMjhCGCNLsWQsw26gRxDy62UXRCTCT3iR qHP82dxPdNwXuOFG7IzoGBMm3vZbBeKn0pYYWz2MbTeyRHn+ZubNHqM0cv5gh0FWsQxrg1ss pnhcd+qgoynfuWAhrPD2YtNB7s1Vyfk3OzmL7DkSDI4+SzS56cnl9Q4mmnsVh9eyae74pv5w kJXy3grazD1lLp+Fq60Iilc09FtWKOg/2JlGD6ZreSnECLrawMPTnHQZEIBHx/VLsoyCFMmO 5P6gU0a9sQWG3F2MLwjnQ5yDPS4IRvLB0aCu+zRfx6mz1zYbcVToVxQqWsz2HTqlP2ZE5cdy BGrQZUkKkNH7oQYXAQyZh42WJo6UFesaRAPc3KCOCFAsDXz19cc9l6uvHnSo/OAazf/RKtTE 0xGB6mQN34UAEQEAAcLA9gQYAQoAIAIbDBYhBHeyd+fQfcCoBrAfeCeIT8WGARmGBQJeORkW AAoJECeIT8WGARmGXtgL/jM4NXaPxaIptPG6XnVWxhAocjk4GyoUx14nhqxHmFi84DmHUpMz 8P0AEACQ8eJb3MwfkGIiauoBLGMX2NroXcBQTi8gwT/4u4Gsmtv6P27Isn0hrY7hu7AfgvnK owfBV796EQo4i26ZgfSPng6w7hzCR+6V2ypdzdW8xXZlvA1D+gLHr1VGFA/ZCXvVcN1lQvIo S9yXo17bgy+/Xxi2YZGXf9AZ9C+g/EvPgmKrUPuKi7ATNqloBaN7S2UBJH6nhv618bsPgPqR SV11brVF8s5yMiG67WsogYl/gC2XCj5qDVjQhs1uGgSc9LLVdiKHaTMuft5gSR9hS5sMb/cL zz3lozuC5nsm1nIbY62mR25Kikx7N6uL7TAZQWazURzVRe1xq2MqcF+18JTDdjzn53PEbg7L VeNDGqQ5lJk+rATW2VAy8zasP2/aqCPmSjlCogC6vgCot9mj+lmMkRUxspxCHDEms13K41tH RzDVkdgPJkL/NFTKZHo5foFXNi89kA== In-Reply-To: <20260516152714.GBagiM0u1QN-6QAjUX@fat_crate.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 16.05.26 17:27, Borislav Petkov wrote: > On Fri, May 15, 2026 at 06:11:46PM +0200, Mathias Krause wrote: >> Funny to see how x86 maintainer options completely disagree on this, see >> https://lore.kernel.org/lkml/739e4dd0-84a3-4b37-8cc3-b7ec59737010@intel.com/ > > You mean we should have an internal meeting first to agree on maintainer > policy so that we can have a common, unified messaging to the rest of the > community...? ?!? > > Or are we allowed to disagree and find the most optimal solution in the > process? Of course you are. However, it would be nice to object in time and not make a contributor implement N iterations, each being different, just because the next maintainer didn't like the previous version. Or, at least, other maintainers chiming in and commenting to the direction change from their proposal. Neither happened here. I mean, it's a stupid debugging feature, how perfect does it need to be? > > Pfff. > >> No, it should not, as that's only for the user portion >> (X86_FEATURE_USER_SHSTK != X86_FEATURE_SHSTK). >> >> Even though there is (currently) no kernel level shadow stack support, >> KVM may still want to pass it down to guests for their usage -- even if >> the host *userland* shouldn't make use of it because of "nousershstk". > > So do a global "disable control-flow enforcement" thing which disables all > related features, as Rick points out. Sorry, I can't figure which suggestion of Rick you are referring to but maybe you're mixing it up with that?: https://lore.kernel.org/lkml/bf9738e1-330e-4c87-a294-e8dce100ffc2@grsecurity.net/ > > That one should dump a warning saying what also it disables and that it should > be a debugging option. And I'm thinking it probably should taint the kernel > too because we don't want people left'n'right to turn off shadow stacks and > then complain... This is getting ridiculous. It's a debug feature by nature and it feels like clearcpuid=shstk would almost perfectly match above requirements. > > Btw, this is my own opinion and just a suggestion - not a x86 maintainer > stance. I'm throwing this out so that someone else can propose a better one > and we arrive at the proper solution eventually. I.e., as we have always done > it on the mailing list... > Yeah, I'm out. We just handle this downstream. Thanks, Mathias