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[85.187.217.62]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9ee0e2f096sm827883666b.200.2024.11.13.01.28.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Nov 2024 01:28:01 -0800 (PST) Message-ID: <4dfb0169-ac37-4c93-8c3b-e8e21a73d8c8@suse.com> Date: Wed, 13 Nov 2024 11:28:00 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC][PATCH] x86/cpu/bugs: Consider having old Intel microcode to be a vulnerability To: Dave Hansen , Alex Murray , dave.hansen@linux.intel.com Cc: bp@alien8.de, linux-kernel@vger.kernel.org, tglx@linutronix.de, x86@kernel.org References: <87v7wtvty0.fsf@canonical.com> <1c1015f8-1a47-4e5b-b088-f83054d2f613@intel.com> From: Nikolay Borisov Content-Language: en-US In-Reply-To: <1c1015f8-1a47-4e5b-b088-f83054d2f613@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 12.11.24 г. 17:51 ч., Dave Hansen wrote: > On 11/11/24 22:37, Alex Murray wrote: >>> == Microcode Revision Discussion == >>> >>> The microcode versions in the table were generated from the Intel >>> microcode git repo: >>> >>> 29f82f7429c ("microcode-20241029 Release") >> >> This upstream microcode release only contained an update for a >> functional issue[1] - not any fixes for security issues. So it would not >> really be correct to say a machine running the previous microcode >> revision is vulnerable. > > There are literally two things this patch "says". One is in userspace > and can be literally read as: > > /sys/devices/system/cpu/vulnerabilities/old_microcode > > "You are vulnerable to old CPU microcode". > > The other is in the code: X86_BUG_OLD_MICROCODE. Which can literally be > read to say "you have a CPU bug called 'old microcode'. (Oh, and I guess > this comes out in /proc/cpuinfo too). > > If you think this is confusing, we can document our way out of it or > revise the changelog. But we kinda get to define what the file and the > X86_BUG mean in the first place. > > I don't really see how it's possible to argue that they're "incorrect". > >> As such, should the table of microcode revisions only be generated >> from the upstream microcode releases that contain fixes for security >> issues? > > No, I don't think so. First, I honestly don't want to have this > discussion every three months where folks can argue about whether a > given microcode release is functional or security. Or, even worse, > which individual microcode *image* is which. > > Second, running kernels with functional issues is *BAD*. As a kernel > policy, we don't want users running with old microcode. Security bugs > only hurt our users but functional bugs hurt the kernel too because > users blame the kernel when they hit them and kernel developers spend > time chasing those issues down. Probably the same reasoning can be applied here as for the CVEs - since the kernel (microcode) is a very fundamental piece of software, almost any issue can be treated as a security one (at least judging from the influx of automatically generated CVEs). By the same token we can assume that microcode always fixes a critical issue :) > > So I guess it boils down to: First, should we tell users when their > microcode is old? If so, how should we do it? >