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

[Brijesh Singh]

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.si...@amd.com>
---
 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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