[RFC PATCH v1 26/28] KVM: SVM: add KVM_SEV_DEBUG_DECRYPT command

[Brijesh Singh <brijesh.singh@xxxxxxx>]

The command decrypts a page of guest memory for debugging purposes.

For more information see [1], section 7.1

[1] http://support.amd.com/TechDocs/55766_SEV-KM%20API_Spec.pdf

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/kvm/svm.c |   83 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 63e7d15..b383bc7 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5606,6 +5606,84 @@ err_1:
 	return ret;
 }
 
+static int __sev_dbg_decrypt_page(struct kvm *kvm, unsigned long src,
+				  void *dst, int *psp_ret)
+{
+	int ret, pinned;
+	struct page **inpages;
+	struct psp_data_dbg *decrypt;
+
+	decrypt = kzalloc(sizeof(*decrypt), GFP_KERNEL);
+	if (!decrypt)
+		return -ENOMEM;
+
+	ret = -ENOMEM;
+	inpages = kzalloc(1 * sizeof(struct page *), GFP_KERNEL);
+	if (!inpages)
+		goto err_1;
+
+	/* pin the user virtual address */
+	ret = -EFAULT;
+	down_read(&current->mm->mmap_sem);
+	pinned = get_user_pages(src, 1, 1, 0, inpages, NULL);
+	up_read(&current->mm->mmap_sem);
+	if (pinned < 0)
+		goto err_2;
+
+	decrypt->hdr.buffer_len = sizeof(*decrypt);
+	decrypt->handle = kvm_sev_handle();
+	decrypt->dst_addr = __pa(dst) | sme_me_mask;
+	decrypt->src_addr = __sev_page_pa(inpages[0]);
+	decrypt->length = PAGE_SIZE;
+
+	ret = psp_dbg_decrypt(decrypt, psp_ret);
+	if (ret)
+		printk(KERN_ERR "SEV: DEBUG_DECRYPT %d (%#010x)\n",
+				ret, *psp_ret);
+	release_pages(inpages, 1, 0);
+err_2:
+	kfree(inpages);
+err_1:
+	kfree(decrypt);
+	return ret;
+}
+
+static int sev_dbg_decrypt(struct kvm *kvm,
+			   struct kvm_sev_dbg_decrypt __user *argp,
+			   int *psp_ret)
+{
+	void *data;
+	int ret, offset, len;
+	struct kvm_sev_dbg_decrypt debug;
+
+	if (!kvm_sev_guest())
+		return -ENOTTY;
+
+	if (copy_from_user(&debug, argp, sizeof(*argp)))
+		return -EFAULT;
+
+	if (debug.length > PAGE_SIZE)
+		return -EINVAL;
+
+	data = (void *) get_zeroed_page(GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	/* decrypt one page */
+	ret = __sev_dbg_decrypt_page(kvm, debug.src_addr, data, psp_ret);
+	if (ret)
+		goto err_1;
+
+	/* we have decrypted full page but copy request length */
+	offset = debug.src_addr & (PAGE_SIZE - 1);
+	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_sev_issue_cmd(struct kvm *kvm,
 			     struct kvm_sev_issue_cmd __user *user_data)
 {
@@ -5636,6 +5714,11 @@ static int amd_sev_issue_cmd(struct kvm *kvm,
 					&arg.ret_code);
 		break;
 	}
+	case KVM_SEV_DBG_DECRYPT: {
+		r = sev_dbg_decrypt(kvm, (void *)arg.opaque,
+					&arg.ret_code);
+		break;
+	}
 	default:
 		break;
 	}

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