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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1wba1L-0000000HCHO-3ygg; Mon, 22 Jun 2026 08:28:44 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id D0349300B5F; Mon, 22 Jun 2026 10:28:41 +0200 (CEST) Date: Mon, 22 Jun 2026 10:28:41 +0200 From: Peter Zijlstra To: Guo Ren Cc: Kees Cook , arnd@arndb.de, palmer@rivosinc.com, tglx@linutronix.de, luto@kernel.org, conor.dooley@microchip.com, heiko@sntech.de, jszhang@kernel.org, lazyparser@gmail.com, falcon@tinylab.org, chenhuacai@kernel.org, apatel@ventanamicro.com, atishp@atishpatra.org, mark.rutland@arm.com, bjorn@kernel.org, palmer@dabbelt.com, bjorn@rivosinc.com, daniel.thompson@linaro.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, stable@vger.kernel.org, Guo Ren Subject: Re: [PATCH] riscv: entry: Fixup do_trap_break from kernel side Message-ID: <20260622082841.GW49951@noisy.programming.kicks-ass.net> References: <20230702025708.784106-1-guoren@kernel.org> <202606191652.38297DE51@keescook> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Sun, Jun 21, 2026 at 02:52:46AM -0400, Guo Ren wrote: > On Fri, Jun 19, 2026 at 04:54:53PM -0700, Kees Cook wrote: > > *thread encromancy* > > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > > From: Guo Ren > > > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > > debug the kernel. > > > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > > of the kernel side. > > > > > > Before the fixup: > > > $echo BUG > /sys/kernel/debug/provoke-crash/DIRECT > > > lkdtm: Performing direct entry BUG > > > ------------[ cut here ]------------ > > > kernel BUG at drivers/misc/lkdtm/bugs.c:78! > > > [...] > > > Kernel panic - not syncing: Aiee, killing interrupt handler! > > > > This appears to still be unfixed. What's the blocker? The solutions in > > this thread seem to work... > > > > I'd like to be exercising an Oops path via KUnit (for KCFI), and riscv > > just instantly falls over instead of thread-killing on the exception. > Thanks for reviving this thread. At the time I didn’t fully understand > Peter’s point. We should only use the NMI path when the trap occurs with > interrupts disabled. > Here’s the updated fix: > > do_trap_break(struct pt_regs *regs) > ... > irqentry_exit_to_user_mode(regs); > } else { > - irqentry_state_t state = irqentry_nmi_enter(regs); > + if (regs->status & SR_IE) { > + enum ctx_state prev_state = exception_enter(); > > - handle_break(regs); > + handle_break(regs); > > - irqentry_nmi_exit(regs, state); > + exception_exit(prev_state); > + } else { > + irqentry_state_t state = irqentry_nmi_enter(regs); > + > + handle_break(regs); > + > + irqentry_nmi_exit(regs, state); > + } > } > } > > If you & Peter have no objection, I’ll post a v2. I still don't understand it. This cannot fix anything. Consider: EBREAK raw_spin_lock_irq(&your_lock) EBREAK So now the first 'works', but the second will crash. Additionally, having the EBREAK context differ so dramatically between invocations seems like a very bad deal to me.