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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1j7drL-0003fH-0Z; Fri, 28 Feb 2020 11:31:11 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1j7drF-0003eu-Kf for linux-arm-kernel@lists.infradead.org; Fri, 28 Feb 2020 11:31:09 +0000 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 C3C994B2; Fri, 28 Feb 2020 03:31:04 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3AB753F73B; Fri, 28 Feb 2020 03:31:03 -0800 (PST) Date: Fri, 28 Feb 2020 11:31:01 +0000 From: Mark Rutland To: Will Deacon Subject: Re: [PATCH 2/2] arm64: kprobe: disable probe of fault prone ptrauth instruction Message-ID: <20200228113100.GC36089@lakrids.cambridge.arm.com> References: <1582117240-15330-1-git-send-email-amit.kachhap@arm.com> <1582117240-15330-3-git-send-email-amit.kachhap@arm.com> <20200227164817.GA31259@lakrids.cambridge.arm.com> <52db2533-488a-1e27-947c-ec92048f26ae@arm.com> <20200228111856.GB2941@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200228111856.GB2941@willie-the-truck> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200228_033107_612310_1FF394B5 X-CRM114-Status: GOOD ( 19.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kees Cook , Suzuki K Poulose , Catalin Marinas , Kristina Martsenko , Mark Brown , James Morse , Amit Kachhap , Vincenzo Frascino , Dave Martin , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Feb 28, 2020 at 11:18:59AM +0000, Will Deacon wrote: > On Fri, Feb 28, 2020 at 04:42:10PM +0530, Amit Kachhap wrote: > > On 2/27/20 10:18 PM, Mark Rutland wrote: > > > On Wed, Feb 19, 2020 at 06:30:40PM +0530, Amit Daniel Kachhap wrote: > > > > diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c > > > > index 4a9e773..87f7c8a 100644 > > > > --- a/arch/arm64/kernel/insn.c > > > > +++ b/arch/arm64/kernel/insn.c > > > > @@ -63,6 +63,7 @@ bool __kprobes aarch64_insn_is_nop(u32 insn) > > > > case AARCH64_INSN_HINT_WFI: > > > > case AARCH64_INSN_HINT_SEV: > > > > case AARCH64_INSN_HINT_SEVL: > > > > + case AARCH64_INSN_HINT_AUTIASP: > > > > return false; > > > > default: > > > > return true; > > > > > > I'm afraid that the existing code here is simply wrong, and this is > > > adding to the mess. > > > > > > We have no idea what HINT space instructions will be in the future, so > > > the only sensible implementations of aarch64_insn_is_nop() are something > > > like: > > > > > > bool __kprobes aarch64_insn_is_nop(u32 insn) > > > { > > > return insn == aarch64_insn_gen_hint(AARCH64_INSN_HINT_NOP); > > > } > > > > > > ... and if we want to check for other HINT instructions, they should be > > > checked explicitly. > > > > > > Can you please change aarch64_insn_is_nop() as above? > > > > Agree that current implementation is unclear. > > I will implement as you suggested. > > Well, please don't throw the baby out with the bath water. The existing > code might be badly structured, but I think it's going a bit far to say > it's "simply wrong". We need a whitelist /somewhere/ and I'd prefer not > to regress the existing behaviour just because the whitelist is embedded > in a function with "is_nop" in the name. Ok; we can follow up with a more complete cleanup after these patches have been merged. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel