[RFC PATCH v2 29/32] kvm: svm: Add support for SEV DEBUG_DECRYPT command

[Brijesh Singh <brijesh.singh@xxxxxxx>]

The command is used to decrypt guest memory region for debug purposes.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/kvm/svm.c |   76 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 977aa22..ce8819a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5986,6 +5986,78 @@ static int sev_guest_status(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
+static int __sev_dbg_decrypt_page(struct kvm *kvm, unsigned long src,
+		void *dst, int *error)
+{
+	int ret;
+	struct page **inpages;
+	struct sev_data_dbg *data;
+	unsigned long npages;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	inpages = sev_pin_memory(src, PAGE_SIZE, &npages);
+	if (!inpages) {
+		ret = -ENOMEM;
+		goto err_1;
+	}
+
+	data->handle = sev_get_handle(kvm);
+	data->dst_addr = __psp_pa(dst);
+	data->src_addr = __sev_page_pa(inpages[0]);
+	data->length = PAGE_SIZE;
+
+	ret = sev_issue_cmd(kvm, SEV_CMD_DBG_DECRYPT, data, error);
+	if (ret)
+		printk(KERN_ERR "SEV: DEBUG_DECRYPT %d (%#010x)\n",
+				ret, *error);
+	sev_unpin_memory(inpages, npages);
+err_1:
+	kfree(data);
+	return ret;
+}
+
+static int sev_dbg_decrypt(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	void *data;
+	int ret, offset, len;
+	struct kvm_sev_dbg debug;
+
+	if (!sev_guest(kvm))
+		return -ENOTTY;
+
+	if (copy_from_user(&debug, (void *)argp->data,
+				sizeof(struct kvm_sev_dbg)))
+		return -EFAULT;
+	/*
+	 * TODO: add support for decrypting length which crosses the
+	 * page boundary.
+	 */
+	offset = debug.src_addr & (PAGE_SIZE - 1);
+	if (offset + debug.length > PAGE_SIZE)
+		return -EINVAL;
+
+	data = (void *) get_zeroed_page(GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	/* decrypt full page */
+	ret = __sev_dbg_decrypt_page(kvm, debug.src_addr & PAGE_MASK,
+			data, &argp->error);
+	if (ret)
+		goto err_1;
+
+	/* we have decrypted full page but copy request length */
+	len = min_t(size_t, (PAGE_SIZE - offset), debug.length);
+	if (copy_to_user((uint8_t *)debug.dst_addr, data + offset, len))
+		ret = -EFAULT;
+err_1:
+	free_page((unsigned long)data);
+	return ret;
+}
+
 static int amd_memory_encryption_cmd(struct kvm *kvm, void __user *argp)
 {
 	int r = -ENOTTY;
@@ -6013,6 +6085,10 @@ static int amd_memory_encryption_cmd(struct kvm *kvm, void __user *argp)
 		r = sev_guest_status(kvm, &sev_cmd);
 		break;
 	}
+	case KVM_SEV_DBG_DECRYPT: {
+		r = sev_dbg_decrypt(kvm, &sev_cmd);
+		break;
+	}
 	default:
 		break;
 	}