Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

[qemu.git] / qemu-doc.texi

diff --git a/qemu-doc.texi b/qemu-doc.texi
index 8022890391b55ea3ced360a10bfa9e44fc2c7bf6..ad31f2d2d0d8047ceb578eb8dca5517ba7cea47d 100644 (file)
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -214,7 +214,7 @@ PCI UHCI USB controller and a virtual USB hub.
 
 SMP is supported with up to 255 CPUs.
 
-QEMU uses the PC BIOS from the Bochs project and the Plex86/Bochs LGPL
+QEMU uses the PC BIOS from the Seabios project and the Plex86/Bochs LGPL
 VGA BIOS.
 
 QEMU uses YM3812 emulation by Tatsuyuki Satoh.
@@ -536,21 +536,38 @@ support of multiple VM snapshots.
 Supported options:
 @table @code
 @item compat
-Determines the qcow2 version to use. @code{compat=0.10} uses the traditional
-image format that can be read by any QEMU since 0.10 (this is the default).
+Determines the qcow2 version to use. @code{compat=0.10} uses the
+traditional image format that can be read by any QEMU since 0.10.
 @code{compat=1.1} enables image format extensions that only QEMU 1.1 and
-newer understand. Amongst others, this includes zero clusters, which allow
-efficient copy-on-read for sparse images.
+newer understand (this is the default). Amongst others, this includes
+zero clusters, which allow efficient copy-on-read for sparse images.
 
 @item backing_file
 File name of a base image (see @option{create} subcommand)
 @item backing_fmt
 Image format of the base image
 @item encryption
-If this option is set to @code{on}, the image is encrypted.
+If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC.
+
+The use of encryption in qcow and qcow2 images is considered to be flawed by
+modern cryptography standards, suffering from a number of design problems:
+
+@itemize @minus
+@item The AES-CBC cipher is used with predictable initialization vectors based
+on the sector number. This makes it vulnerable to chosen plaintext attacks
+which can reveal the existence of encrypted data.
+@item The user passphrase is directly used as the encryption key. A poorly
+chosen or short passphrase will compromise the security of the encryption.
+@item In the event of the passphrase being compromised there is no way to
+change the passphrase to protect data in any qcow images. The files must
+be cloned, using a different encryption passphrase in the new file. The
+original file must then be securely erased using a program like shred,
+though even this is ineffective with many modern storage technologies.
+@end itemize
 
-Encryption uses the AES format which is very secure (128 bit keys). Use
-a long password (16 characters) to get maximum protection.
+Use of qcow / qcow2 encryption is thus strongly discouraged. Users are
+recommended to use an alternative encryption technology such as the
+Linux dm-crypt / LUKS system.
 
 @item cluster_size
 Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
@@ -654,6 +671,21 @@ Supported options:
 Specifies which VHD subformat to use. Valid options are
 @code{dynamic} (default) and @code{fixed}.
 @end table
+
+@item VHDX
+Hyper-V compatible image format (VHDX).
+Supported options:
+@table @code
+@item subformat
+Specifies which VHDX subformat to use. Valid options are
+@code{dynamic} (default) and @code{fixed}.
+@item block_state_zero
+Force use of payload blocks of type 'ZERO'.
+@item block_size
+Block size; min 1 MB, max 256 MB.  0 means auto-calculate based on image size.
+@item log_size
+Log size; min 1 MB.
+@end table
 @end table
 
 @subsubsection Read-only formats