Re: [RFC] rust: kernel: Add KUnit tests for ARCH_WARN_ASM bug table emission

From: Heiko Carstens <hca@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mukesh Kumar Chaurasiya <mkchauras@gmail.com>,
	catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com,
	maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com,
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	pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu,
	alex@ghiti.fr, gor@linux.ibm.com, agordeev@linux.ibm.com,
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	linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
	rust-for-linux@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [RFC] rust: kernel: Add KUnit tests for ARCH_WARN_ASM bug table emission
Date: Thu, 24 Sep 2026 17:13:35 +0200	[thread overview]
Message-ID: <20260924151335.18402A8b-hca@linux.ibm.com> (raw)
In-Reply-To: <20260924111557.GP1837346@noisy.programming.kicks-ass.net>

On Thu, Sep 24, 2026 at 01:15:57PM +0200, Peter Zijlstra wrote:
> Untested thingies for arm64 and s390x.
...
> diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
> index b6ba4465f59d..8bbb082fd5e3 100644
> --- a/arch/s390/kernel/traps.c
> +++ b/arch/s390/kernel/traps.c
> @@ -26,6 +26,7 @@
>  #include <linux/entry-common.h>
>  #include <linux/kmsan.h>
>  #include <linux/bug.h>
> +#include <linux/uaccess.h>
>  #include <asm/entry-percpu.h>
>  #include <asm/asm-extable.h>
>  #include <asm/irqflags.h>
> @@ -55,7 +56,12 @@ static inline void __user *get_trap_ip(struct pt_regs *regs)
>  #ifdef CONFIG_GENERIC_BUG
>  int is_valid_bugaddr(unsigned long addr)
>  {
> -	return 1;
> +	u16 insn;
> +
> +	if (get_kernel_nofault(insn, (u16 *)addr))
> +		return 0;
> +
> +	return insn == 0x0001 || insn == 0x000e;

I have no idea why anybody wants to do this, but it looks like I'm not
alone :) In any case: the check is wrong.
s390 uses only the monitor call instruction and this should be

	return insn == 0xaf00;

At least it is not possible to set a kprobe on bug instructions, which
would make this "interesting".

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