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McKenney" , Boqun Feng , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Michael Kerrisk , Joel Fernandes Message-ID: <2135166002.2147.1526571001678.JavaMail.zimbra@efficios.com> In-Reply-To: <20180517133230.GA2688@arm.com> References: <20180430224433.17407-1-mathieu.desnoyers@efficios.com> <20180430224433.17407-4-mathieu.desnoyers@efficios.com> <20180516161809.GH12198@hirez.programming.kicks-ass.net> <670368504.1912.1526501593893.JavaMail.zimbra@efficios.com> <20180517133230.GA2688@arm.com> Subject: Re: [PATCH 03/14] arm: Add restartable sequences support 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_2026 (ZimbraWebClient - FF52 (Linux)/8.8.8_GA_2031) Thread-Topic: Add restartable sequences support Thread-Index: hkDF4Yy2rYjeT3UBbYbe4+QoPict4g== Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: ----- On May 17, 2018, at 9:32 AM, Will Deacon will.deacon@arm.com wrote: > On Wed, May 16, 2018 at 04:13:13PM -0400, Mathieu Desnoyers wrote: >> ----- On May 16, 2018, at 12:18 PM, Peter Zijlstra peterz@infradead.org wrote: >> >> > On Mon, Apr 30, 2018 at 06:44:22PM -0400, Mathieu Desnoyers wrote: >> >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >> >> index a7f8e7f4b88f..4f5c386631d4 100644 >> >> --- a/arch/arm/Kconfig >> >> +++ b/arch/arm/Kconfig >> >> @@ -91,6 +91,7 @@ config ARM >> >> select HAVE_PERF_USER_STACK_DUMP >> >> select HAVE_RCU_TABLE_FREE if (SMP && ARM_LPAE) >> >> select HAVE_REGS_AND_STACK_ACCESS_API >> >> + select HAVE_RSEQ >> >> select HAVE_SYSCALL_TRACEPOINTS >> >> select HAVE_UID16 >> >> select HAVE_VIRT_CPU_ACCOUNTING_GEN >> >> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c >> >> index bd8810d4acb3..5879ab3f53c1 100644 >> >> --- a/arch/arm/kernel/signal.c >> >> +++ b/arch/arm/kernel/signal.c >> >> @@ -541,6 +541,12 @@ static void handle_signal(struct ksignal *ksig, struct >> >> pt_regs *regs) >> >> int ret; >> >> >> >> /* >> >> + * Increment event counter and perform fixup for the pre-signal >> >> + * frame. >> >> + */ >> >> + rseq_signal_deliver(regs); >> >> + >> >> + /* >> >> * Set up the stack frame >> >> */ >> >> if (ksig->ka.sa.sa_flags & SA_SIGINFO) >> >> @@ -660,6 +666,7 @@ do_work_pending(struct pt_regs *regs, unsigned int >> >> thread_flags, int syscall) >> >> } else { >> >> clear_thread_flag(TIF_NOTIFY_RESUME); >> >> tracehook_notify_resume(regs); >> >> + rseq_handle_notify_resume(regs); >> >> } >> >> } >> >> local_irq_disable(); >> > >> > I think you forgot to hook up rseq_syscall() checking. >> >> Considering that rseq_syscall is implemented as follows: >> >> +void rseq_syscall(struct pt_regs *regs) >> +{ >> + unsigned long ip = instruction_pointer(regs); >> + struct task_struct *t = current; >> + struct rseq_cs rseq_cs; >> + >> + if (!t->rseq) >> + return; >> + if (!access_ok(VERIFY_READ, t->rseq, sizeof(*t->rseq)) || >> + rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs)) >> + force_sig(SIGSEGV, t); >> +} >> >> and that x86 calls it from syscall_return_slowpath() (which AFAIU is >> now used in the fast-path since KPTI), I wonder where we should call >> this on ARM ? I was under the impression that ARM return to userspace >> fast-path was not calling C code unless work flags were set, but I might >> be wrong. >> >> Thoughts ? > > Since this only matters for CONFIG_DEBUG_RSEQ, can we just force the > slowpath for rseq tasks when that option is set? Or as proposed by Boqun, we can simply call rseq_syscall in a CONFIG_DEBUG_RSEQ ifdef. Given that this is a debug option, is it worth it to add the current->rseq test for NULL in assembly before the call, or do we want to favor simplicity ? Thanks, Mathieu > > Will -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com