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([2601:646:c200:1ef2:a08d:668a:535c:86e9]) by smtp.gmail.com with ESMTPSA id g63sm43128219pfc.127.2019.04.27.06.59.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 27 Apr 2019 06:59:37 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall From: Andy Lutomirski X-Mailer: iPhone Mail (16E227) In-Reply-To: <20190426180235.GC9835@mit.edu> Date: Sat, 27 Apr 2019 06:59:36 -0700 Cc: Eric Biggers , "Reshetova, Elena" , "herbert@gondor.apana.org.au" , David Laight , Ingo Molnar , Peter Zijlstra , "keescook@chromium.org" , Daniel Borkmann , "luto@kernel.org" , "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" Content-Transfer-Encoding: quoted-printable Message-Id: <1EB25EC8-28A4-46C6-84E9-14858B68C815@amacapital.net> References: <01914abbfc1a4053897d8d87a63e3411@AcuMS.aculab.com> <20190416154348.GB3004@mit.edu> <2236FBA76BA1254E88B949DDB74E612BA4C52338@IRSMSX102.ger.corp.intel.com> <9cf586757eb44f2c8f167abf078da921@AcuMS.aculab.com> <20190417151555.GG4686@mit.edu> <99e045427125403ba2b90c2707d74e02@AcuMS.aculab.com> <2236FBA76BA1254E88B949DDB74E612BA4C5E473@IRSMSX102.ger.corp.intel.com> <2236FBA76BA1254E88B949DDB74E612BA4C63E24@IRSMSX102.ger.corp.intel.com> <20190426140102.GA4922@mit.edu> <20190426174419.GB691@sol.localdomain> <20190426180235.GC9835@mit.edu> To: Theodore Ts'o Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Apr 26, 2019, at 11:02 AM, Theodore Ts'o wrote: >=20 >> On Fri, Apr 26, 2019 at 10:44:20AM -0700, Eric Biggers wrote: >> Would it be possibly to call ChaCha20 through the actual crypto API so th= at SIMD >> instructions (e.g. AVX-2) could be used? That would make it *much* faste= r. >> Also consider AES-CTR with AES-NI instructions. >=20 > It's not obvious SIMD instructions will be faster in practice, since > it requires saving and restoring the vector/FPU registers. If you're > going to be doing a *lot* of vector processing (for example when doing > block-level RAID-5 / RAID-6 computations), it might be worth it. But > if you're only going to be turning the crank for 12 or 20 rounds, the > overhead of calling kernel_fpu_begin() and kernel_fpu_end() is > probably going to make this worth it. >=20 So generate a whole page or more of random bytes at a time and save them up f= or when they=E2=80=99re needed.=