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[209.85.167.49]) by smtp.gmail.com with ESMTPSA id g20sm173120lja.67.2019.05.03.12.19.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 03 May 2019 12:19:16 -0700 (PDT) Received: by mail-lf1-f49.google.com with SMTP id u27so4886300lfg.10 for ; Fri, 03 May 2019 12:19:15 -0700 (PDT) X-Received: by 2002:a19:4f54:: with SMTP id a20mr5886095lfk.136.1556910664485; Fri, 03 May 2019 12:11:04 -0700 (PDT) MIME-Version: 1.0 References: <57357E35-3D9B-4CA7-BAB9-0BE89E0094D2@amacapital.net> <2236FBA76BA1254E88B949DDB74E612BA4C66A8A@IRSMSX102.ger.corp.intel.com> <6860856C-6A92-4569-9CD8-FF6C5C441F30@amacapital.net> <2236FBA76BA1254E88B949DDB74E612BA4C6A4D7@IRSMSX102.ger.corp.intel.com> <303fc4ee5ac04e4fac104df1188952e8@AcuMS.aculab.com> <2236FBA76BA1254E88B949DDB74E612BA4C6C2C3@IRSMSX102.ger.corp.intel.com> <2e55aeb3b39440c0bebf47f0f9522dd8@AcuMS.aculab.com> <20190502150853.GA16779@gmail.com> <20190502164524.GB115950@gmail.com> <2236FBA76BA1254E88B949DDB74E612BA4C6F523@IRSMSX102.ger.corp.intel.com> In-Reply-To: From: Linus Torvalds Date: Fri, 3 May 2019 12:10:48 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall To: David Laight Cc: "Reshetova, Elena" , Ingo Molnar , Andy Lutomirski , "Theodore Ts'o" , Eric Biggers , "ebiggers@google.com" , "herbert@gondor.apana.org.au" , Peter Zijlstra , "keescook@chromium.org" , Daniel Borkmann , "linux-kernel@vger.kernel.org" , "jpoimboe@redhat.com" , "jannh@google.com" , "Perla, Enrico" , "mingo@redhat.com" , "bp@alien8.de" , "tglx@linutronix.de" , "gregkh@linuxfoundation.org" , "Edgecombe, Rick P" , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 3, 2019 at 9:40 AM David Laight wrote: > > That gives you 10 system calls per rdrand instruction > and mostly takes the latency out of line. Do we really want to do this? What is the attack scenario? With no VLA's, and the stackleak plugin, what's the upside? Are we adding random code (literally) "just because"? Linus