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 52E3315491 for ; Tue, 16 Jul 2024 11:41:06 +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=1721130068; cv=none; b=QkCkTXM3vIBtC5Xn1RwtCrsiF4/F4aNwSFwPHlJjmKN2iGh1BKZf7RJXjkTtwQuMbWSk5I9SdhVTgQ5rRRJjZ+zRQLHlOEJdYFGpIVSrrdS38t+El0HLXSzjEdXQdyv5LRN1Ls9iaSjlW6BoCKDf+fMwrLxUJlMrT/vmEqfnsZc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721130068; c=relaxed/simple; bh=cPqUIIzgMa1VyzU8Q0SG76h08e/UGrYGch/lA75gQqc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NyGywW3vDTM3cArenp2Jn/Ey25ZNgc/na8jUomu5n+SpbOISRIKgbelshujnjUbfhTobezE/of6zQGXI1SDojWiZ0PvWAL7h5h/1lVLgmqXQB+VHGOUAKdTUSl0GkCYxZOQRG8EtwJQtUIsQ+d+18NT5oThJeMiwjwfmfPq9HWc= 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; 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 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 B19091063; Tue, 16 Jul 2024 04:41:30 -0700 (PDT) Received: from [10.163.52.225] (unknown [10.163.52.225]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BB35A3F766; Tue, 16 Jul 2024 04:40:54 -0700 (PDT) Message-ID: Date: Tue, 16 Jul 2024 17:10:50 +0530 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 17/29] arm64: implement PKEYS support To: Kevin Brodsky , Joey Gouly , linux-arm-kernel@lists.infradead.org Cc: akpm@linux-foundation.org, aneesh.kumar@kernel.org, aneesh.kumar@linux.ibm.com, bp@alien8.de, broonie@kernel.org, catalin.marinas@arm.com, christophe.leroy@csgroup.eu, dave.hansen@linux.intel.com, hpa@zytor.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, maz@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, naveen.n.rao@linux.ibm.com, npiggin@gmail.com, oliver.upton@linux.dev, shuah@kernel.org, szabolcs.nagy@arm.com, tglx@linutronix.de, will@kernel.org, x86@kernel.org, kvmarm@lists.linux.dev References: <20240503130147.1154804-1-joey.gouly@arm.com> <20240503130147.1154804-18-joey.gouly@arm.com> <18aee949-7e07-45e1-85c8-c990f017f305@arm.com> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <18aee949-7e07-45e1-85c8-c990f017f305@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/9/24 18:37, Kevin Brodsky wrote: > On 03/05/2024 15:01, Joey Gouly wrote: >> @@ -267,6 +294,28 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm) >> return -1UL >> 8; >> } >> >> +/* >> + * We only want to enforce protection keys on the current process >> + * because we effectively have no access to POR_EL0 for other >> + * processes or any way to tell *which * POR_EL0 in a threaded >> + * process we could use. > > I see that this comment is essentially copied from x86, but to me it > misses the main point. Even with only one thread in the target process > and a way to obtain its POR_EL0, it still wouldn't make sense to check > that value. If we take the case of a debugger accessing an inferior via > ptrace(), for instance, the kernel is asked to access some memory in > another mm. However, the debugger's POR_EL0 is tied to its own address > space, and the target's POR_EL0 is relevant to its own execution flow > only. In such situations, there is essentially no user context for the > access, so It fundamentally does not make sense to make checks based on > pkey/POE or similar restrictions to memory accesses (e.g. MTE). Indeed this makes more sense. There is no memory context even if there is access to another POR_EL0. The comment above could be improved describing this limitation.