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SEV: disable SEV-ES DebugSwap by default

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The DebugSwap feature of SEV-ES provides a way for confidential guests to use
data breakpoints.  However, because the status of the DebugSwap feature is
recorded in the VMSA, enabling it by default invalidates the attestation
signatures.  In 6.10 we will introduce a new API to create SEV VMs that
will allow enabling DebugSwap based on what the user tells KVM to do.
Contextually, we will change the legacy KVM_SEV_ES_INIT API to never
enable DebugSwap.

For compatibility with kernels that pre-date the introduction of DebugSwap,
as well as with those where KVM_SEV_ES_INIT will never enable it, do not enable
the feature by default.  If anybody wants to use it, for now they can enable
the sev_es_debug_swap_enabled module parameter, but this will result in a
warning.

Fixes: d1f85fbe83 ("KVM: SEV: Enable data breakpoints in SEV-ES")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-03-09 11:24:58 -05:00
parent 39fee313fd
commit 5abf6dceb0
1 changed files with 5 additions and 2 deletions
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7
arch/x86/kvm/svm/sev.c
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@ -57,7 +57,7 @@ static bool sev_es_enabled = true;
module_param_named(sev_es, sev_es_enabled, bool, 0444);
/* enable/disable SEV-ES DebugSwap support */
static bool sev_es_debug_swap_enabled = true;
static bool sev_es_debug_swap_enabled = false;
module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0444);
#else
#define sev_enabled false
@ -612,8 +612,11 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
save->xss = svm->vcpu.arch.ia32_xss;
save->dr6 = svm->vcpu.arch.dr6;
if (sev_es_debug_swap_enabled)
if (sev_es_debug_swap_enabled) {
save->sev_features |= SVM_SEV_FEAT_DEBUG_SWAP;
pr_warn_once("Enabling DebugSwap with KVM_SEV_ES_INIT. "
"This will not work starting with Linux 6.10\n");
}
pr_debug("Virtual Machine Save Area (VMSA):\n");
print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, save, sizeof(*save), false);