Re: [PATCH] riscv: entry: Fixup do_trap_break from kernel side

From: Guo Ren <guoren@kernel.org>
To: Kees Cook <kees@kernel.org>
Cc: arnd@arndb.de, palmer@rivosinc.com, tglx@linutronix.de,
	peterz@infradead.org, 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 <guoren@linux.alibaba.com>
Subject: Re: [PATCH] riscv: entry: Fixup do_trap_break from kernel side
Date: Sun, 21 Jun 2026 02:52:46 -0400	[thread overview]
Message-ID: <ajeKPpg2rwadVPY4@gmail.com> (raw)
In-Reply-To: <202606191652.38297DE51@keescook>

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 <guoren@linux.alibaba.com>
> > 
> > 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.

Best Regards
  GUO Ren