linux-kernel - [PATCH v3 0/4] Add SEV-SNP CipherTextHiding feature support

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Message-ID: <cover.1745279916.git.ashish.kalra@amd.com>
Date: Tue, 22 Apr 2025 00:24:00 +0000
From: Ashish Kalra <Ashish.Kalra@....com>
To: <seanjc@...gle.com>, <pbonzini@...hat.com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<hpa@...or.com>, <herbert@...dor.apana.org.au>
CC: <x86@...nel.org>, <john.allen@....com>, <davem@...emloft.net>,
	<thomas.lendacky@....com>, <michael.roth@....com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-crypto@...r.kernel.org>
Subject: [PATCH v3 0/4] Add SEV-SNP CipherTextHiding feature support

From: Ashish Kalra <ashish.kalra@....com>

Ciphertext hiding prevents host accesses from reading the ciphertext
of SNP guest private memory. Instead of reading ciphertext, the host
will see constant default values (0xff).

Ciphertext hiding separates the ASID space into SNP guest ASIDs and 
host ASIDs. All SNP active guests must have an ASID less than or
equal to MAX_SNP_ASID provided to the SNP_INIT_EX command.
All SEV-legacy guests must be greater than MAX_SNP_ASID.

This patch-set adds two new module parameters to the KVM module
to enable SNP CipherTextHiding support and user configurable
MAX_SNP_ASID to define the system-wide maximum SNP ASID value.
If this value is not set, then the ASID space is equally divided
between SEV-SNP and SEV-ES guests.

v3:
- rebase to linux-next.
- rebase on top of support to move SEV-SNP initialization to
KVM module from CCP driver.
- Split CipherTextHiding support between CCP driver and KVM module
with KVM module calling into CCP driver to initialize SNP with
CipherTextHiding enabled and MAX ASID usable for SNP guest if
KVM is enabling CipherTextHiding feature.
- Move module parameters to enable CipherTextHiding feature and
MAX ASID usable for SNP guests from CCP driver to KVM module
which allows KVM to be responsible for enabling CipherTextHiding
feature if end-user requests it.

v2:
- Fix and add more description to commit logs.
- Rename sev_cache_snp_platform_status_and_discover_features() to 
snp_get_platform_data().
- Add check in snp_get_platform_data to guard against being called
after SNP_INIT_EX.
- Fix comments for new structure field definitions being added.
- Fix naming for new structure being added.
- Add new vm-type parameter to sev_asid_new().
- Fix identation.
- Rename CCP module parameters psp_cth_enabled to cipher_text_hiding and 
psp_max_snp_asid to max_snp_asid.
- Rename max_snp_asid to snp_max_snp_asid. 

Ashish Kalra (4):
  crypto: ccp: New bit-field definitions for SNP_PLATFORM_STATUS command
  crypto: ccp: Add support for SNP_FEATURE_INFO command
  crypto: ccp: Add support to enable CipherTextHiding on SNP_INIT_EX
  KVM: SVM: Add SEV-SNP CipherTextHiding support

 arch/x86/kvm/svm/sev.c       | 50 ++++++++++++++++++++---
 drivers/crypto/ccp/sev-dev.c | 78 ++++++++++++++++++++++++++++++++++--
 drivers/crypto/ccp/sev-dev.h |  3 ++
 include/linux/psp-sev.h      | 47 +++++++++++++++++++++-
 include/uapi/linux/psp-sev.h | 10 ++++-
 5 files changed, 177 insertions(+), 11 deletions(-)

-- 
2.34.1