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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id h3sm415376pju.33.2021.09.29.12.26.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Sep 2021 12:26:31 -0700 (PDT) Date: Wed, 29 Sep 2021 12:26:30 -0700 From: Kees Cook To: Mark Brown Cc: Josh Poimboeuf , Mark Rutland , Vito Caputo , Jann Horn , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Jens Axboe , Peter Zijlstra , Stefan Metzmacher , Andy Lutomirski , Lai Jiangshan , Christian Brauner , Andrew Morton , "Kenta.Tada@sony.com" , Daniel Bristot de Oliveira , Michael =?iso-8859-1?Q?Wei=DF?= , Anand K Mistry , Alexey Gladkov , Michal Hocko , Helge Deller , Dave Hansen , Andrea Righi , Ohhoon Kwon , Kalesh Singh , YiFei Zhu , "Eric W. Biederman" , Qi Zheng , linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] proc: Disable /proc/$pid/wchan Message-ID: <202109291224.8C538667@keescook> References: <20210924002230.sijoedia65hf5bj7@shells.gnugeneration.com> <202109231814.FD09DBAD3@keescook> <20210924135424.GA33573@C02TD0UTHF1T.local> <202109240716.A0792BE46@keescook> <20210927090337.GB1131@C02TD0UTHF1T.local> <202109271103.4E15FC0@keescook> <20210927205056.jjdlkof5w6fs5wzw@treble> <202109291152.681444A135@keescook> <20210929190042.GU4199@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210929190042.GU4199@sirena.org.uk> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 29, 2021 at 08:00:42PM +0100, Mark Brown wrote: > On Wed, Sep 29, 2021 at 11:54:55AM -0700, Kees Cook wrote: > > On Mon, Sep 27, 2021 at 01:50:56PM -0700, Josh Poimboeuf wrote: > > > > Even with that patch, it doesn't lock the task's runqueue before reading > > > the stack, so there's still the possibility of the task running on > > > another CPU and the unwinder going off the rails a bit, which might be > > > used by an attacker in creative ways similar to the /proc//stack > > > vulnerability Jann mentioned earlier. > > > Since I think we're considering get_wchan() to be slow-path, can we just > > lock the runqueue and use arch_stack_walk_reliable()? > > Unfortunately arch_stack_walk_reliable() is only available for powerpc, > s390 and x86 currently - work is in progress to implement it for arm64 > as well but it's not there yet. Strictly speaking, we're only trying to fix this for x86+ORC. The other architectures (or non-ORC x86) already have their own non-ORC unwinders behind get_wchan(). They may have similar weaknesses (which should certainly be fixed), I think the first step here is to restore wchan under x86+ORC. -- Kees Cook