From: Jeremy Linton <jeremy.linton@arm.com>
To: Andre Przywara <andre.przywara@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, stefan.wahren@i2se.com,
mlangsdo@redhat.com, suzuki.poulose@arm.com,
marc.zyngier@arm.com, catalin.marinas@arm.com,
julien.thierry@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, steven.price@arm.com,
ykaukab@suse.de, dave.martin@arm.com, shankerd@codeaurora.org
Subject: Re: [PATCH v4 07/12] arm64: add sysfs vulnerability show for meltdown
Date: Thu, 31 Jan 2019 15:53:16 -0600 [thread overview]
Message-ID: <394041d0-a738-84f0-56a7-6803d4180113@arm.com> (raw)
In-Reply-To: <20190131175418.24b7811c@donnerap.cambridge.arm.com>
Hi,
On 01/31/2019 11:54 AM, Andre Przywara wrote:
> On Fri, 25 Jan 2019 12:07:06 -0600
> Jeremy Linton <jeremy.linton@arm.com> wrote:
>
> Hi,
>
>> Display the mitigation status if active, otherwise
>> assume the cpu is safe unless it doesn't have CSV3
>> and isn't in our whitelist.
>>
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>> arch/arm64/kernel/cpufeature.c | 33 +++++++++++++++++++++++++++------
>> 1 file changed, 27 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/cpufeature.c
>> b/arch/arm64/kernel/cpufeature.c
>> index a9e18b9cdc1e..624dfe0b5cdd 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -944,6 +944,8 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
>> return has_cpuid_feature(entry, scope);
>> }
>>
>> +/* default value is invalid until unmap_kernel_at_el0() runs */
>
> Shall we somehow enforce this? For instance by making __meltdown_safe
> an enum, initialised to UNKNOWN?
Hehe, well I think people complained about my "UNKNOWN" enum. But, in
the end this version is trying to make it clear we shouldn't have any
unknown states remaining.
> Then bail out with a BUG_ON or WARN_ON in the sysfs code?
AFAIK, it shouldn't be possible to actually run the sysfs code before
this gets initialized. So, the comment is just making it clear/forcing
the understanding of that.
>
> I just want to avoid to accidentally report "safe" when we actually
> aren't.
>
>> +static bool __meltdown_safe = true;
>> static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
>> static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>> @@ -962,6 +964,16 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>> { /* sentinel */ }
>> };
>> char const *str = "command line option";
>> + bool meltdown_safe;
>> +
>> + meltdown_safe = is_midr_in_range_list(read_cpuid_id(), kpti_safe_list);
>> +
>> + /* Defer to CPU feature registers */
>> + if (has_cpuid_feature(entry, scope))
>> + meltdown_safe = true;
>> +
>> + if (!meltdown_safe)
>> + __meltdown_safe = false;
>>
>> /*
>> * For reasons that aren't entirely clear, enabling KPTI on Cavium
>> @@ -984,12 +996,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>> if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
>> return kaslr_offset() > 0;
>>
>> - /* Don't force KPTI for CPUs that are not vulnerable */
>> - if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list))
>> - return false;
>> -
>> - /* Defer to CPU feature registers */
>> - return !has_cpuid_feature(entry, scope);
>> + return !meltdown_safe;
>> }
>>
>> static void
>> @@ -2055,3 +2062,17 @@ 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)
>
> w/s issue.
>
> Cheers,
> Andre.
>
>> +{
>> + if (arm64_kernel_unmapped_at_el0())
>> + return sprintf(buf, "Mitigation: KPTI\n");
>> +
>> + if (__meltdown_safe)
>> + return sprintf(buf, "Not affected\n");
>> +
>> + return sprintf(buf, "Vulnerable\n");
>> +}
>> +#endif
>
next prev parent reply other threads:[~2019-01-31 21:53 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-25 18:06 [PATCH v4 00/12] arm64: add system vulnerability sysfs entries Jeremy Linton
2019-01-25 18:07 ` [PATCH v4 01/12] Documentation: Document arm64 kpti control Jeremy Linton
2019-01-30 18:02 ` Andre Przywara
2019-02-06 19:24 ` Jeremy Linton
2019-02-06 21:06 ` André Przywara
2019-01-31 17:58 ` Andre Przywara
2019-02-07 0:25 ` Jonathan Corbet
2019-01-25 18:07 ` [PATCH v4 02/12] arm64: Provide a command line to disable spectre_v2 mitigation Jeremy Linton
2019-01-30 18:03 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 03/12] arm64: Remove the ability to build a kernel without ssbd Jeremy Linton
2019-01-30 18:04 ` Andre Przywara
2019-02-15 18:20 ` Catalin Marinas
2019-02-15 18:54 ` Jeremy Linton
2019-01-25 18:07 ` [PATCH v4 04/12] arm64: remove the ability to build a kernel without hardened branch predictors Jeremy Linton
2019-01-30 18:04 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 05/12] arm64: remove the ability to build a kernel without kpti Jeremy Linton
2019-01-30 18:05 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 06/12] arm64: add sysfs vulnerability show for spectre v1 Jeremy Linton
2019-01-31 17:52 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 07/12] arm64: add sysfs vulnerability show for meltdown Jeremy Linton
2019-01-31 9:28 ` Julien Thierry
2019-01-31 21:48 ` Jeremy Linton
2019-01-31 17:54 ` Andre Przywara
2019-01-31 21:53 ` Jeremy Linton [this message]
2019-01-25 18:07 ` [PATCH v4 08/12] arm64: Advertise mitigation of Spectre-v2, or lack thereof Jeremy Linton
2019-01-31 17:54 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 09/12] arm64: Use firmware to detect CPUs that are not affected by Spectre-v2 Jeremy Linton
2019-01-31 17:55 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 10/12] arm64: add sysfs vulnerability show for spectre v2 Jeremy Linton
2019-01-31 17:55 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 11/12] arm64: add sysfs vulnerability show for speculative store bypass Jeremy Linton
2019-01-31 17:55 ` Andre Przywara
2019-01-25 18:07 ` [PATCH v4 12/12] arm64: enable generic CPU vulnerabilites support Jeremy Linton
2019-01-31 17:56 ` Andre Przywara
2019-02-08 20:05 ` [PATCH v4 00/12] arm64: add system vulnerability sysfs entries Stefan Wahren
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