From: Jeremy Linton <jeremy.linton@arm.com>
To: Julien Thierry <julien.thierry@arm.com>,
linux-arm-kernel@lists.infradead.org
Cc: stefan.wahren@i2se.com, mlangsdo@redhat.com,
suzuki.poulose@arm.com, marc.zyngier@arm.com,
catalin.marinas@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 v3 4/7] arm64: add sysfs vulnerability show for meltdown
Date: Thu, 10 Jan 2019 08:10:43 -0600 [thread overview]
Message-ID: <7e843245-56c0-d7c1-38ba-27ff231a500a@arm.com> (raw)
In-Reply-To: <8c8b564a-1d65-bc18-73fb-58b349a47800@arm.com>
Hi Julien,
On 01/10/2019 03:23 AM, Julien Thierry wrote:
> Hi Jeremy,
>
> On 09/01/2019 23:55, Jeremy Linton wrote:
>> 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 | 32 +++++++++++++++++++++++++++-----
>> 1 file changed, 27 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index ab784d7a0083..ef7bbc49ef78 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -944,8 +944,12 @@ 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 */
>> +static bool __meltdown_safe = true;
>> +
>> #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>> static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
>> +extern uint arm64_requested_vuln_attrs;
>>
>> static bool is_cpu_meltdown_safe(void)
>> {
>> @@ -972,6 +976,14 @@ 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);
>> +
>> + if (!meltdown_safe)
>> + __meltdown_safe = false;
>> +
>> + arm64_requested_vuln_attrs |= VULN_MELTDOWN;
>> +
>> /*
>> * For reasons that aren't entirely clear, enabling KPTI on Cavium
>> * ThunderX leads to apparent I-cache corruption of kernel text, which
>> @@ -993,11 +1005,7 @@ 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
>> @@ -2065,3 +2073,17 @@ 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)
>> + return sprintf(buf, "Not affected\n");
>
> An issue I see is that we don't even bother to check it that CPUs are
> meltdown safe if CONFIG_UNMAP_KERNEL_AT_EL0 is not defined but here
> we'll advertise that the system is meltdown safe.
That check isn't necessary anymore because the sysfs attribute is only
populated if unmap_kernel_at_el0() runs (assuming I haven't messed
something up). That was Dave/Will's suggestions in the last thread about
how to handle this case.
>
> I think that checking whether we know that CPUs are meltdown safe should
> be separated from whether mitigation is applied.
>
> Someone who knows thinks their CPUs are in the white list might want to
> compile out code that does the kpti, but it would be good to give them a
> proper diagnostic whether they were wrong or not.
>
> Cheers,
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-01-10 14:11 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 23:55 [PATCH v3 0/7] arm64: add system vulnerability sysfs entries Jeremy Linton
2019-01-09 23:55 ` [PATCH v3 1/7] sysfs/cpu: Allow individual architectures to select vulnerabilities Jeremy Linton
2019-01-14 10:02 ` Suzuki K Poulose
2019-01-18 15:46 ` Greg KH
2019-01-18 16:31 ` Jeremy Linton
2019-01-09 23:55 ` [PATCH v3 2/7] arm64: add sysfs vulnerability show for spectre v1 Jeremy Linton
2019-01-09 23:55 ` [PATCH v3 3/7] arm64: kpti: move check for non-vulnerable CPUs to a function Jeremy Linton
2019-01-12 10:41 ` Stefan Wahren
2019-01-14 11:32 ` Suzuki K Poulose
2019-01-18 16:35 ` Jeremy Linton
2019-01-09 23:55 ` [PATCH v3 4/7] arm64: add sysfs vulnerability show for meltdown Jeremy Linton
2019-01-10 9:23 ` Julien Thierry
2019-01-10 14:10 ` Jeremy Linton [this message]
2019-01-10 14:16 ` Julien Thierry
2019-01-09 23:55 ` [PATCH v3 5/7] arm64: add sysfs vulnerability show for spectre v2 Jeremy Linton
2019-01-09 23:55 ` [PATCH v3 6/7] arm64: add sysfs vulnerability show for speculative store bypass Jeremy Linton
2019-01-14 10:15 ` Marc Zyngier
2019-01-14 16:37 ` Jeremy Linton
2019-01-14 17:05 ` Marc Zyngier
2019-01-09 23:55 ` [PATCH v3 7/7] arm64: enable generic CPU vulnerabilites support Jeremy Linton
2019-01-15 19:50 ` [PATCH v3 0/7] arm64: add system vulnerability sysfs entries Stefan Wahren
2019-01-15 21:21 ` Jeremy Linton
2019-01-18 18:05 ` Stefan Wahren
2019-01-18 22:22 ` Jeremy Linton
2019-01-19 11:52 ` Stefan Wahren
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=7e843245-56c0-d7c1-38ba-27ff231a500a@arm.com \
--to=jeremy.linton@arm.com \
--cc=catalin.marinas@arm.com \
--cc=dave.martin@arm.com \
--cc=julien.thierry@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=marc.zyngier@arm.com \
--cc=mlangsdo@redhat.com \
--cc=shankerd@codeaurora.org \
--cc=stefan.wahren@i2se.com \
--cc=steven.price@arm.com \
--cc=suzuki.poulose@arm.com \
--cc=will.deacon@arm.com \
--cc=ykaukab@suse.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).