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McKenney" , Boqun Feng , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , Michal Simek , schwidefsky , gor Message-ID: <1368400582.11897.1530643261772.JavaMail.zimbra@efficios.com> In-Reply-To: <20180703182837.GC2494@hirez.programming.kicks-ass.net> References: <858886246.10882.1530583291379.JavaMail.zimbra@efficios.com> <20180703173451.GX2494@hirez.programming.kicks-ass.net> <399697782.11820.1530639539750.JavaMail.zimbra@efficios.com> <20180703174833.GZ2494@hirez.programming.kicks-ass.net> <1048940999.11846.1530640717837.JavaMail.zimbra@efficios.com> <20180703181143.GB2494@hirez.programming.kicks-ass.net> <1708848118.11868.1530641734202.JavaMail.zimbra@efficios.com> <20180703182837.GC2494@hirez.programming.kicks-ass.net> Subject: Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.8_GA_2096 (ZimbraWebClient - FF52 (Linux)/8.8.8_GA_1703) Thread-Topic: rseq: use __u64 for rseq_cs fields, validate user inputs Thread-Index: SR4kmDGS9PpmQ3sS6yVWOtbnSeZRbg== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jul 3, 2018, at 2:28 PM, Peter Zijlstra peterz@infradead.org wrote: > On Tue, Jul 03, 2018 at 02:15:34PM -0400, Mathieu Desnoyers wrote: >> ----- On Jul 3, 2018, at 2:11 PM, Peter Zijlstra peterz@infradead.org wrote: >> >> > On Tue, Jul 03, 2018 at 01:58:37PM -0400, Mathieu Desnoyers wrote: >> >> I can modify the ABI to put the cpu_id_start and cpu_id fields inside >> >> a union, and update it with a single store. >> >> >> >> Thoughts ? >> > >> > Let's keep them for now, we can always frob this later, they are aligned >> > and proper, no need to expose that union to userspace. >> >> Isn't it weird to change the API of an exposed public uapi header ? > > Sure, just keep it as is. We don't need an exposed union to do a single > store there. > > Something like the ugly below preserves API but still does a single > store. > > But sure, if you want to expose that union for some reason, then now is > the time. User-space won't ever want to read cpu_id_start and cpu_id from a single u64 load, it serves no purpose to do so. So I'm OK with keeping those as is and defining a local union for the __put_user() update. Thanks! Mathieu > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index 22b6acf1ad63..e956c48b5f83 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -85,10 +85,17 @@ static int rseq_update_cpu_id(struct task_struct *t) > { > u32 cpu_id = raw_smp_processor_id(); > > - if (__put_user(cpu_id, &t->rseq->cpu_id_start)) > - return -EFAULT; > - if (__put_user(cpu_id, &t->rseq->cpu_id)) > + union { > + struct { > + u32 cpu_id_start; > + u32 cpu_id; > + }; > + u64 val; > + } x = { { .cpu_id_start = cpu_id, .cpu_id = cpu_id, } }; > + > + if (__put_user(x.val, (u64 *)&t->rseq->cpu_id_start)) > return -EFAULT; > + > trace_rseq_update(t); > return 0; > } -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com