Messages in this thread Patch in this message | | | Date | Fri, 26 Jan 2018 12:25:19 +0000 | From | Dave Martin <> | Subject | Re: [PATCH 10/16] arm64: Make KPTI strict CPU local feature |
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On Tue, Jan 23, 2018 at 12:28:03PM +0000, Suzuki K Poulose wrote: > KPTI capability is a security feature which should be enabled > when at least one CPU on the system needs it. Any late CPU > which needs the kernel support, should be prevented from > booting (and thus making the system unsecure) if the feature > was not already enabled.
Is there an actual change to behaviour here?
It's not very obvious from the commit message, or the patch when read in isolation.
> > Cc: Will Deacon <will.deacon@arm.com> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > --- > arch/arm64/kernel/cpufeature.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 111f6c4b4cd7..2627a836e99d 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -862,9 +862,8 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus > 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,
[Nit: All the other .matches functions have a predicate-style name, so "should_unmap_kernel_at_el0" or "must_unmap_kernel_at_el0" might be better names... However, the name wasn't introduced by this series and it's not a huge deal.]
> - int __unused) > + int scope) > { > - u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1); > > /* Forced on command line? */ > if (__kpti_forced) { > @@ -878,8 +877,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > return true; > > /* Defer to CPU feature registers */ > - return !cpuid_feature_extract_unsigned_field(pfr0, > - ID_AA64PFR0_CSV3_SHIFT); > + return !has_cpuid_feature(entry, scope); > } > > static int __init parse_kpti(char *str) > @@ -1003,7 +1001,10 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > { > .desc = "Kernel page table isolation (KPTI)", > .capability = ARM64_UNMAP_KERNEL_AT_EL0, > - .type = ARM64_CPUCAP_BOOT_SYSTEM_FEATURE, > + .type = ARM64_CPUCAP_STRICT_CPU_LOCAL_FEATURE, > + .sys_reg = SYS_ID_AA64PFR0_EL1, > + .field_pos = ID_AA64PFR0_CSV3_SHIFT, > + .min_field_value = 1, > .matches = unmap_kernel_at_el0, > }, > #endif
[...]
Cheers ---Dave
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