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

[Brijesh Singh]

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

Signed-off-by: Brijesh Singh <brijesh.si...@amd.com>
---
 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;
        }