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Mon, 20 Apr 2020 15:24:34 -0700 (PDT) Date: Mon, 20 Apr 2020 15:24:28 -0700 From: Sami Tolvanen To: Will Deacon Subject: Re: [PATCH v11 03/12] scs: add support for stack usage debugging Message-ID: <20200420222428.GB77284@google.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20200416161245.148813-1-samitolvanen@google.com> <20200416161245.148813-4-samitolvanen@google.com> <20200420171741.GC24386@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200420171741.GC24386@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200420_152437_658063_D0F459F9 X-CRM114-Status: GOOD ( 14.72 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Juri Lelli , kernel-hardening@lists.openwall.com, Peter Zijlstra , Catalin Marinas , Marc Zyngier , Masahiro Yamada , clang-built-linux@googlegroups.com, Ingo Molnar , Laura Abbott , Dave Martin , Kees Cook , Jann Horn , Steven Rostedt , linux-arm-kernel@lists.infradead.org, Michal Marek , Ard Biesheuvel , Nick Desaulniers , linux-kernel@vger.kernel.org, Miguel Ojeda , James Morse , Masami Hiramatsu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Apr 20, 2020 at 06:17:42PM +0100, Will Deacon wrote: > > +#ifdef CONFIG_DEBUG_STACK_USAGE > > +static inline unsigned long scs_used(struct task_struct *tsk) > > +{ > > + unsigned long *p = __scs_base(tsk); > > + unsigned long *end = scs_magic(p); > > + unsigned long s = (unsigned long)p; > > + > > + while (p < end && READ_ONCE_NOCHECK(*p)) > > + p++; > > I think the expectation is that the caller has already checked that the > stack is not corrupted, so I'd probably throw a couple of underscores > in front of the function name, along with a comment. Correct. I'll do that. > Also, is tsk ever != current? This is only called from scs_release(), so tsk is never current. > > +static void scs_check_usage(struct task_struct *tsk) > > +{ > > + static DEFINE_SPINLOCK(lock); > > + static unsigned long highest; > > + unsigned long used = scs_used(tsk); > > + > > + if (used <= highest) > > + return; > > + > > + spin_lock(&lock); > > + > > + if (used > highest) { > > + pr_info("%s (%d): highest shadow stack usage: %lu bytes\n", > > + tsk->comm, task_pid_nr(tsk), used); > > + highest = used; > > + } > > + > > + spin_unlock(&lock); > > Do you really need this lock? I'd have thought you could cmpxchg() > highest instead. This is similar to check_stack_usage in kernel/exit.c, but yes, I can change this to a cmpxchg() loop instead. Sami _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel