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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q5-20020a17090a4f8500b001fbb0f0b00fsm10907573pjh.35.2022.10.03.21.37.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Oct 2022 21:37:07 -0700 (PDT) Date: Mon, 3 Oct 2022 21:37:06 -0700 From: Kees Cook To: Andy Lutomirski Cc: Rick Edgecombe , x86@kernel.org, "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V . Shankar" , Weijiang Yang , "Kirill A . Shutemov" , joao.moreira@intel.com, John Allen , kcc@google.com, eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com, dethoma@microsoft.com Subject: Re: [PATCH v2 29/39] x86/cet/shstk: Support wrss for userspace Message-ID: <202210032129.44F6E027D@keescook> References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> <20220929222936.14584-30-rick.p.edgecombe@intel.com> <202210031525.78F3FA8@keescook> <6ea0841f-5086-9569-028b-922ec01a9196@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6ea0841f-5086-9569-028b-922ec01a9196@kernel.org> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664858229; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=xlDrlQKwusKzG3w+2ZOP4CcXq+zZWkgG9x1cLqQziDo=; b=8Qzx8BzOHJVznlS7mbojgnHgBB+2fWDnIYbANomss3mjTp766VJsxhoqKLJSomw2iaz1vE jZchKUDTsjiDV+I5hqtPmctyO0G396+gzZa/ESXJQG+xGuAoFGrzGflh1cVRMobm4SYxlx glFbxdgDoLStnAZIb9B0og9mPP+/ksA= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="odgDB/DE"; spf=pass (imf01.hostedemail.com: domain of keescook@chromium.org designates 209.85.216.51 as permitted sender) smtp.mailfrom=keescook@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664858229; a=rsa-sha256; cv=none; b=HJwLECJtwpxKxHWo8boB1ChNgv9K/sYwa5w+UY7+r4OGmzJseoE0a9PARtxTpALm3gOsU2 tZF7Iyc+HvXXE+FZLGWB3O80RJLgCJnQW2Ah0tYrZm8lWwJdbeMr71dlG0LxrfrfWhaVPX 1hN93U0OuIlMdaHwsp3EnH5IkkpAh8o= Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="odgDB/DE"; spf=pass (imf01.hostedemail.com: domain of keescook@chromium.org designates 209.85.216.51 as permitted sender) smtp.mailfrom=keescook@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 586FF4001E X-Rspam-User: X-Stat-Signature: c8pscsg3d5dseisp7mgy3wukd69rm58w X-HE-Tag: 1664858229-132142 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Oct 03, 2022 at 04:00:36PM -0700, Andy Lutomirski wrote: > On 10/3/22 15:28, Kees Cook wrote: > > On Thu, Sep 29, 2022 at 03:29:26PM -0700, Rick Edgecombe wrote: > > > For the current shadow stack implementation, shadow stacks contents easily > > > be arbitrarily provisioned with data. > > > > I can't parse this sentence. > > > > > This property helps apps protect > > > themselves better, but also restricts any potential apps that may want to > > > do exotic things at the expense of a little security. > > > > Is anything using this right now? Wouldn't thing be safer without WRSS? > > (Why can't we skip this patch?) > > > > So that people don't write programs that need either (shstk off) or (shstk > on and WRSS on) and crash or otherwise fail on kernels that support shstk > but don't support WRSS, perhaps? Right, yes. I meant more "what programs currently need WRSS to operate under shstk? (And what is it that they are doing that needs it?)" All is see currently is compiler self-tests and emulators using it? https://codesearch.debian.net/search?q=%5Cb%28wrss%7CWRSS%29%5Cb&literal=0&perpkg=1 -- Kees Cook