KVM: SVM: Add support for SEV DEBUG_ENCRYPT command

The command copies a plaintext into guest memory and encrypts it using
the VM encryption key. The command will be used for debug purposes
(e.g setting breakpoints through gdbserver)

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

arch/x86/kvm/svm.c

@@ -6240,6 +6240,83 @@ static int __sev_dbg_decrypt_user(struct kvm *kvm, unsigned long paddr,
 	return ret;
 }
 
+static int __sev_dbg_encrypt_user(struct kvm *kvm, unsigned long paddr,
+				  unsigned long __user vaddr,
+				  unsigned long dst_paddr,
+				  unsigned long __user dst_vaddr,
+				  int size, int *error)
+{
+	struct page *src_tpage = NULL;
+	struct page *dst_tpage = NULL;
+	int ret, len = size;
+
+	/* If source buffer is not aligned then use an intermediate buffer */
+	if (!IS_ALIGNED(vaddr, 16)) {
+		src_tpage = alloc_page(GFP_KERNEL);
+		if (!src_tpage)
+			return -ENOMEM;
+
+		if (copy_from_user(page_address(src_tpage),
+				(void __user *)(uintptr_t)vaddr, size)) {
+			__free_page(src_tpage);
+			return -EFAULT;
+		}
+
+		paddr = __sme_page_pa(src_tpage);
+	}
+
+	/*
+	 *  If destination buffer or length is not aligned then do read-modify-write:
+	 *   - decrypt destination in an intermediate buffer
+	 *   - copy the source buffer in an intermediate buffer
+	 *   - use the intermediate buffer as source buffer
+	 */
+	if (!IS_ALIGNED(dst_vaddr, 16) || !IS_ALIGNED(size, 16)) {
+		int dst_offset;
+
+		dst_tpage = alloc_page(GFP_KERNEL);
+		if (!dst_tpage) {
+			ret = -ENOMEM;
+			goto e_free;
+		}
+
+		ret = __sev_dbg_decrypt(kvm, dst_paddr,
+					__sme_page_pa(dst_tpage), size, error);
+		if (ret)
+			goto e_free;
+
+		/*
+		 *  If source is kernel buffer then use memcpy() otherwise
+		 *  copy_from_user().
+		 */
+		dst_offset = dst_paddr & 15;
+
+		if (src_tpage)
+			memcpy(page_address(dst_tpage) + dst_offset,
+			       page_address(src_tpage), size);
+		else {
+			if (copy_from_user(page_address(dst_tpage) + dst_offset,
+					   (void __user *)(uintptr_t)vaddr, size)) {
+				ret = -EFAULT;
+				goto e_free;
+			}
+		}
+
+		paddr = __sme_page_pa(dst_tpage);
+		dst_paddr = round_down(dst_paddr, 16);
+		len = round_up(size, 16);
+	}
+
+	ret = __sev_issue_dbg_cmd(kvm, paddr, dst_paddr, len, error, true);
+
+e_free:
+	if (src_tpage)
+		__free_page(src_tpage);
+	if (dst_tpage)
+		__free_page(dst_tpage);
+	return ret;
+}
+
 static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 {
 	unsigned long vaddr, vaddr_end, next_vaddr;
@@ -6292,11 +6369,19 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 		d_off = dst_vaddr & ~PAGE_MASK;
 		len = min_t(size_t, (PAGE_SIZE - s_off), size);
 
-		ret = __sev_dbg_decrypt_user(kvm,
+		if (dec)
-					     __sme_page_pa(src_p[0]) + s_off,
+			ret = __sev_dbg_decrypt_user(kvm,
-					     dst_vaddr,
+						     __sme_page_pa(src_p[0]) + s_off,
-					     __sme_page_pa(dst_p[0]) + d_off,
+						     dst_vaddr,
-					     len, &argp->error);
+						     __sme_page_pa(dst_p[0]) + d_off,
+						     len, &argp->error);
+		else
+			ret = __sev_dbg_encrypt_user(kvm,
+						     __sme_page_pa(src_p[0]) + s_off,
+						     vaddr,
+						     __sme_page_pa(dst_p[0]) + d_off,
+						     dst_vaddr,
+						     len, &argp->error);
 
 		sev_unpin_memory(kvm, src_p, 1);
 		sev_unpin_memory(kvm, dst_p, 1);
@@ -6347,6 +6432,9 @@ static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 	case KVM_SEV_DBG_DECRYPT:
 		r = sev_dbg_crypt(kvm, &sev_cmd, true);
 		break;
+	case KVM_SEV_DBG_ENCRYPT:
+		r = sev_dbg_crypt(kvm, &sev_cmd, false);
+		break;
 	default:
 		r = -EINVAL;
 		goto out;