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Merge tag 'kvm-x86-ciphertext-6.18' of https://github.com/kvm-x86/linux into HEAD

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KVM SEV-SNP CipherText Hiding support for 6.18

Add support for SEV-SNP's CipherText Hiding, an opt-in feature that prevents
unauthorized CPU accesses from reading the ciphertext of SNP guest private
memory, e.g. to attempt an offline attack.  Instead of ciphertext, the CPU
will always read back all FFs when CipherText Hiding is enabled.

Add new module parameter to the KVM module to enable CipherText Hiding and
control the number of ASIDs that can be used for VMs with CipherText Hiding,
which is in effect the number of SNP VMs.  When CipherText Hiding is enabled,
the shared SEV-ES/SEV-SNP ASID space is split into separate ranges for SEV-ES
and SEV-SNP guests, i.e. ASIDs that can be used for CipherText Hiding cannot
be used to run SEV-ES guests.
This commit is contained in:
Paolo Bonzini
2025-09-30 13:34:32 -04:00
parent a104e0a305 6c7c620585
commit 10ef74c06b
6 changed files with 249 additions and 27 deletions
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21
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -2957,6 +2957,27 @@
(enabled). Disable by KVM if hardware lacks support
for NPT.
kvm-amd.ciphertext_hiding_asids=
[KVM,AMD] Ciphertext hiding prevents disallowed accesses
to SNP private memory from reading ciphertext. Instead,
reads will see constant default values (0xff).
If ciphertext hiding is enabled, the joint SEV-ES and
SEV-SNP ASID space is partitioned into separate SEV-ES
and SEV-SNP ASID ranges, with the SEV-SNP range being
[1..max_snp_asid] and the SEV-ES range being
(max_snp_asid..min_sev_asid), where min_sev_asid is
enumerated by CPUID.0x.8000_001F[EDX].
A non-zero value enables SEV-SNP ciphertext hiding and
adjusts the ASID ranges for SEV-ES and SEV-SNP guests.
KVM caps the number of SEV-SNP ASIDs at the maximum
possible value, e.g. specifying -1u will assign all
joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note,
assigning all joint ASIDs to SEV-SNP, i.e. configuring
max_snp_asid == min_sev_asid-1, will effectively make
SEV-ES unusable.
kvm-arm.mode=
[KVM,ARM,EARLY] Select one of KVM/arm64's modes of
operation.