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KVM: arm64: Ensure I-cache isolation between vcpus of a same VM

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Commit 01dc9262ff5797b675c32c0c6bc682777d23de05 upstream.

It recently became apparent that the ARMv8 architecture has interesting
rules regarding attributes being used when fetching instructions
if the MMU is off at Stage-1.

In this situation, the CPU is allowed to fetch from the PoC and
allocate into the I-cache (unless the memory is mapped with
the XN attribute at Stage-2).

If we transpose this to vcpus sharing a single physical CPU,
it is possible for a vcpu running with its MMU off to influence
another vcpu running with its MMU on, as the latter is expected to
fetch from the PoU (and self-patching code doesn't flush below that
level).

In order to solve this, reuse the vcpu-private TLB invalidation
code to apply the same policy to the I-cache, nuking it every time
the vcpu runs on a physical CPU that ran another vcpu of the same
VM in the past.

This involve renaming __kvm_tlb_flush_local_vmid() to
__kvm_flush_cpu_context(), and inserting a local i-cache invalidation
there.

Cc: [email protected]
Signed-off-by: Marc Zyngier <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[maz: added 32bit ARM support]
Signed-off-by: Marc Zyngier <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Marc Zyngier 2021-03-15 11:10:00 +00:00 • committed by Greg Kroah-Hartman
commit da2e37b55d
5 changed files with 13 additions and 5 deletions
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8
virt/kvm/arm/arm.c
View file

@ -373,11 +373,17 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
cpu_data = this_cpu_ptr(&kvm_host_data);
/*
* We guarantee that both TLBs and I-cache are private to each
* vcpu. If detecting that a vcpu from the same VM has
* previously run on the same physical CPU, call into the
* hypervisor code to nuke the relevant contexts.
*
* We might get preempted before the vCPU actually runs, but
* We might get preempted before the vCPU actually runs, but
* over-invalidation doesn't affect correctness.
*/
if (*last_ran != vcpu->vcpu_id) {
kvm_call_hyp(__kvm_tlb_flush_local_vmid, vcpu);
kvm_call_hyp(__kvm_flush_cpu_context, vcpu);
*last_ran = vcpu->vcpu_id;
}