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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gXNDp-0002M4-JY; Thu, 13 Dec 2018 09:23:57 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gXNDm-0002L2-2m for linux-arm-kernel@lists.infradead.org; Thu, 13 Dec 2018 09:23:55 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CCC5415AD; Thu, 13 Dec 2018 01:23:41 -0800 (PST) Received: from [10.1.197.36] (e112298-lin.cambridge.arm.com [10.1.197.36]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 085993F6A8; Thu, 13 Dec 2018 01:23:39 -0800 (PST) Subject: Re: [PATCH 2/6] arm64: add sysfs vulnerability show for meltdown To: Jeremy Linton , linux-arm-kernel@lists.infradead.org References: <20181206234408.1287689-1-jeremy.linton@arm.com> <20181206234408.1287689-3-jeremy.linton@arm.com> From: Julien Thierry Message-ID: Date: Thu, 13 Dec 2018 09:23:38 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181206234408.1287689-3-jeremy.linton@arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181213_012354_133171_81FEFE40 X-CRM114-Status: GOOD ( 22.20 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, suzuki.poulose@arm.com, marc.zyngier@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, ykaukab@suse.de, dave.martin@arm.com, shankerd@codeaurora.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 Hi Jeremy, On 06/12/2018 23:44, Jeremy Linton wrote: > Add a simple state machine which will track whether > all the online cores in a machine are vulnerable. > > Once that is done we have a fairly authoritative view > of the machine vulnerability, which allows us to make a > judgment about machine safety if it hasn't been mitigated. > > Signed-off-by: Jeremy Linton > --- > arch/arm64/kernel/cpufeature.c | 31 ++++++++++++++++++++++++++----- > 1 file changed, 26 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 242898395f68..bea9adfef7fa 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -905,6 +905,8 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope) > return has_cpuid_feature(entry, scope); > } > > +static enum { A64_MELT_UNSET, A64_MELT_SAFE, A64_MELT_UNKN } __meltdown_safe = A64_MELT_UNSET; > + I'm wondering, do we really need that tri state? Can't we consider that we are safe an move to unsafe/unkown if any cpu during bring up is not in the safe list? The only user of this is cpu_show_meltdown, but I don't imagine it'll get called before unmap_kernel_at_el0() is called for the boot CPU which should initialise that state. Or is there another reason for having that UNSET state? Thanks, > #ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */ > > @@ -928,6 +930,15 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > { > char const *str = "command line option"; > > + bool meltdown_safe = is_cpu_meltdown_safe() || > + has_cpuid_feature(entry, scope); > + > + /* Only safe if all booted cores are known safe */ > + if (meltdown_safe && __meltdown_safe == A64_MELT_UNSET) > + __meltdown_safe = A64_MELT_SAFE; > + else if (!meltdown_safe) > + __meltdown_safe = A64_MELT_UNKN; > + > /* > * For reasons that aren't entirely clear, enabling KPTI on Cavium > * ThunderX leads to apparent I-cache corruption of kernel text, which > @@ -949,11 +960,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) > return true; > > - if (is_cpu_meltdown_safe()) > - return false; > - > - /* Defer to CPU feature registers */ > - return !has_cpuid_feature(entry, scope); > + return !meltdown_safe; > } > > static void > @@ -1920,3 +1927,17 @@ static int __init enable_mrs_emulation(void) > } > > core_initcall(enable_mrs_emulation); > + > +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES > +ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, > + char *buf) > +{ > + if (arm64_kernel_unmapped_at_el0()) > + return sprintf(buf, "Mitigation: KPTI\n"); > + > + if (__meltdown_safe == A64_MELT_SAFE) > + return sprintf(buf, "Not affected\n"); > + > + return sprintf(buf, "Unknown\n"); > +} > +#endif > -- Julien Thierry _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel