From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3A17C40A92C for ; Fri, 31 Jul 2026 15:44:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785512682; cv=none; b=nFYydlZ0PDU3fsuyXSK9O595uwiLIUKgm5CUHBcdmCHZRysPa16FpmDcAQhkhTC+XiomdouV1RrgAXOQOlvgt0oCwqAneVAnUsrEBl1nFr/hi8hjJrcISAp9UbjKvgGOHnJ7o8qB9yJ7lEmOkEzlyBd3YgFdWFklj+c2mJFUMv4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785512682; c=relaxed/simple; bh=8IFMauaSRCXOdSY40d+y7wLMdtMeKGcCp3XjsSmhc78=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Fx0go6qEIwUw8szypVCa4kbzuV9c5Gi6FeZrkp0X93vStBbEtkSOud7bMuSdkfYRaGRFwwPUmjgzx/tUDePepoeRoMWhAEqMEvlqZ2yTH0U73WLsQre8knCVDrZCnfnBDAsMOGRJ4C3CDG1UUgC6NPD8PI2VCZ7ragp6zGCvpSs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=RGrQGbe0; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="RGrQGbe0" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8722F204C; Fri, 31 Jul 2026 08:44:35 -0700 (PDT) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 68AEC3F66F; Fri, 31 Jul 2026 08:44:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785512679; bh=8IFMauaSRCXOdSY40d+y7wLMdtMeKGcCp3XjsSmhc78=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RGrQGbe0Evj0ByT/v7EBKvXriDzNi04ME1P8QBWncSGoVGvanh8xa6z4E808fAjnA x0ZGWdNxdLMZmAxRYWi9ZUOkRz+C+5t2E2gIx8PtVc6uMFLHCvziKTuwPr/CxugL5P 2IBvhiqldjKn9muNQJQDObAPCgYf8+XgQoONUJWY= Date: Fri, 31 Jul 2026 16:44:36 +0100 From: Mark Rutland To: Hongyan Xia Cc: Will Deacon , Masami Hiramatsu , Catalin Marinas , Jiazi Li , Pu Hu , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [RFC PATCH 5/9] arm64/kprobes: Invoke pre/post handlers inside instrumentation Message-ID: References: <400e92624124bb2f0efb8757032d1326ccd51d6b.1785153469.git.hongyan.xia@transsion.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <400e92624124bb2f0efb8757032d1326ccd51d6b.1785153469.git.hongyan.xia@transsion.com> On Mon, Jul 27, 2026 at 12:25:41PM +0000, Hongyan Xia wrote: > From: Hongyan Xia > > The kprobe pre_handler() and post_handler() are arbitrary instrumentable > code and can themselves trace, fault, or hit other kprobes. They are > the only parts of the kprobe debug exception flow that legitimately > need instrumentation. That doesn't explain what this patch changes, or why. I'm fine with marking all the kprobe functions noinstr, but we don't need the intrumentation_{begin,end}() gunk. In general, it's not sound for pre_handler and post_handler to invoke arbitrary code, given that they could lead to recursion. We just hope people don't do stupid things with them. Mark. > Signed-off-by: Hongyan Xia > --- > arch/arm64/include/asm/kprobes.h | 9 +++------ > arch/arm64/kernel/probes/kprobes.c | 22 ++++++++++++++++++---- > 2 files changed, 21 insertions(+), 10 deletions(-) > > diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h > index 35ce2c94040e..a694f7d34f45 100644 > --- a/arch/arm64/include/asm/kprobes.h > +++ b/arch/arm64/include/asm/kprobes.h > @@ -48,11 +48,8 @@ void __kprobes *trampoline_probe_handler(struct pt_regs *regs); > > #endif /* CONFIG_KPROBES */ > > -int __kprobes kprobe_brk_handler(struct pt_regs *regs, > - unsigned long esr); > -int __kprobes kprobe_ss_brk_handler(struct pt_regs *regs, > - unsigned long esr); > -int __kprobes kretprobe_brk_handler(struct pt_regs *regs, > - unsigned long esr); > +int noinstr kprobe_brk_handler(struct pt_regs *regs, unsigned long esr); > +int noinstr kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr); > +int noinstr kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr); > > #endif /* _ARM_KPROBES_H */ > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c > index 1b12341b2af3..e9fa66fa4217 100644 > --- a/arch/arm64/kernel/probes/kprobes.c > +++ b/arch/arm64/kernel/probes/kprobes.c > @@ -301,8 +301,11 @@ post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb, struct pt_reg > } > /* call post handler */ > kcb->kprobe_status = KPROBE_HIT_SSDONE; > + > + instrumentation_begin(); > if (cur->post_handler) > cur->post_handler(cur, regs, 0); > + instrumentation_end(); > > reset_current_kprobe(); > } > @@ -359,24 +362,28 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr) > return 0; > } > > -int __kprobes > +int noinstr > kprobe_brk_handler(struct pt_regs *regs, unsigned long esr) > { > struct kprobe *p, *cur_kprobe; > struct kprobe_ctlblk *kcb; > unsigned long addr = instruction_pointer(regs); > + bool handled; > > kcb = get_kprobe_ctlblk(); > cur_kprobe = kprobe_running(); > > + instrumentation_begin(); > p = get_kprobe((kprobe_opcode_t *) addr); > if (WARN_ON_ONCE(!p)) { > + instrumentation_end(); > /* > * Something went wrong. This BRK used an immediate reserved > * for kprobes, but we couldn't find any corresponding probe. > */ > return DBG_HOOK_ERROR; > } > + instrumentation_end(); > > if (cur_kprobe) { > /* Hit a kprobe inside another kprobe */ > @@ -387,6 +394,10 @@ kprobe_brk_handler(struct pt_regs *regs, unsigned long esr) > set_current_kprobe(p); > kcb->kprobe_status = KPROBE_HIT_ACTIVE; > > + instrumentation_begin(); > + handled = p->pre_handler && p->pre_handler(p, regs); > + instrumentation_end(); > + > /* > * If we have no pre-handler or it returned 0, we > * continue with normal processing. If we have a > @@ -394,7 +405,7 @@ kprobe_brk_handler(struct pt_regs *regs, unsigned long esr) > * modify the execution path and not need to single-step > * Let's just reset current kprobe and exit. > */ > - if (!p->pre_handler || !p->pre_handler(p, regs)) > + if (!handled) > setup_singlestep(p, regs, kcb, 0); > else > reset_current_kprobe(); > @@ -403,7 +414,7 @@ kprobe_brk_handler(struct pt_regs *regs, unsigned long esr) > return DBG_HOOK_HANDLED; > } > > -int __kprobes > +int noinstr > kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr) > { > struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); > @@ -422,13 +433,16 @@ kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr) > return DBG_HOOK_ERROR; > } > > -int __kprobes > +int noinstr > kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr) > { > if (regs->pc != (unsigned long)__kretprobe_trampoline) > return DBG_HOOK_ERROR; > > + instrumentation_begin(); > regs->pc = kretprobe_trampoline_handler(regs, (void *)regs->regs[29]); > + instrumentation_end(); > + > return DBG_HOOK_HANDLED; > } > > -- > 2.47.3 >