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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id n22sm100777pjq.36.2020.03.25.13.27.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2020 13:27:03 -0700 (PDT) Date: Wed, 25 Mar 2020 13:27:02 -0700 From: Kees Cook To: "Reshetova, Elena" Cc: Jann Horn , Thomas Gleixner , the arch/x86 maintainers , Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Ard Biesheuvel , Kernel Hardening , "linux-arm-kernel@lists.infradead.org" , Linux-MM , kernel list Subject: Re: [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Message-ID: <202003251322.180F2536E@keescook> References: <20200324203231.64324-1-keescook@chromium.org> <202003241604.7269C810B@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Wed, Mar 25, 2020 at 12:15:12PM +0000, Reshetova, Elena wrote: > > > Also, are you sure that it isn't possible to make the syscall that > > > leaked its stack pointer never return to userspace (via ptrace or > > > SIGSTOP or something like that), and therefore never realign its > > > stack, while keeping some controlled data present on the syscall's > > > stack? > > How would you reliably detect that a stack pointer has been leaked > to userspace while it has been in a syscall? Does not seem to be a trivial > task to me. Well, my expectation is that folks using this defense are also using panic_on_warn sysctl, etc, so attackers don't get a chance to actually _use_ register values spilled to dmesg. -- Kees Cook