Messages in this thread | | | Subject | Re: [PATCH 2/6] arm64: add sysfs vulnerability show for meltdown | From | Jeremy Linton <> | Date | Wed, 12 Dec 2018 08:49:48 -0600 |
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Hi Julien,
Thanks for taking a look at this!
On 12/13/2018 04:46 AM, Julien Thierry wrote: > > > On 13/12/2018 09:23, Julien Thierry wrote: >> 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 <jeremy.linton@arm.com> >>> --- >>> 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? >> > > Ok, I think I get the point of the UNSET as #ifndef > CONFIG_UNMAP_KERNEL_AT_EL0 we don't set the state. But does that mean we > always fall in the "Unknown" case when we don't build kpti in? Is that > desirable? > > If so, I'd suggest replacing the tri-state with the following change: > > >>> + >>> +#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 (!IS_ENABLED(UNMAP_KERNEL_AT_EL0) || !meltdown_safe) > sprintf(buf, "Unknown\n"); > else > sprintf(buf, "Not affected\n");
If I'm understanding what your suggesting:
Isn't this only checking the current core, rather than the whole machine? IIRC that was the fundamental complaint with the original set.
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