Re: [Qemu-devel] [PATCH v2 03/13] migration/ram: add support to send encrypted pages

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Singh, Brijesh (brijesh.singh@amd.com) wrote:
> When memory encryption is enabled, the guest memory will be encrypted with
> the guest specific key. The patch introduces RAM_SAVE_FLAG_ENCRYPTED_PAGE
> flag to distinguish the encrypted data from plaintext. Encrypted pages
> may need special handling. The kvm_memcrypt_save_outgoing_page() is used
> by the sender to write the encrypted pages onto the socket, similarly the
> kvm_memcrypt_load_incoming_page() is used by the target to read the
> encrypted pages from the socket and load into the guest memory.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  migration/ram.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 53 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 908517fc2b..3c8977d508 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -57,6 +57,7 @@
>  #include "qemu/uuid.h"
>  #include "savevm.h"
>  #include "qemu/iov.h"
> +#include "sysemu/kvm.h"
>  
>  /***********************************************************/
>  /* ram save/restore */
> @@ -76,6 +77,7 @@
>  #define RAM_SAVE_FLAG_XBZRLE   0x40
>  /* 0x80 is reserved in migration.h start with 0x100 next */
>  #define RAM_SAVE_FLAG_COMPRESS_PAGE    0x100
> +#define RAM_SAVE_FLAG_ENCRYPTED_PAGE   0x200

OK, that's our very last usable flag!  Use it wisely!

>  static inline bool is_zero_range(uint8_t *p, uint64_t size)
>  {
> @@ -460,6 +462,9 @@ static QemuCond decomp_done_cond;
>  static bool do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block,
>                                   ram_addr_t offset, uint8_t *source_buf);
>  
> +static int ram_save_encrypted_page(RAMState *rs, PageSearchStatus *pss,
> +                                   bool last_stage);
> +
>  static void *do_data_compress(void *opaque)
>  {
>      CompressParam *param = opaque;
> @@ -2006,6 +2011,36 @@ static int ram_save_multifd_page(RAMState *rs, RAMBlock *block,
>      return 1;
>  }
>  
> +/**
> + * ram_save_encrypted_page - send the given encrypted page to the stream
> + */
> +static int ram_save_encrypted_page(RAMState *rs, PageSearchStatus *pss,
> +                                   bool last_stage)
> +{
> +    int ret;
> +    uint8_t *p;
> +    RAMBlock *block = pss->block;
> +    ram_addr_t offset = pss->page << TARGET_PAGE_BITS;
> +    uint64_t bytes_xmit;
> +
> +    p = block->host + offset;
> +
> +    ram_counters.transferred +=
> +        save_page_header(rs, rs->f, block,
> +                    offset | RAM_SAVE_FLAG_ENCRYPTED_PAGE);
> +
> +    ret = kvm_memcrypt_save_outgoing_page(rs->f, p,

I think you need to somehow abstract the kvm_memcrypt stuff; nothing
else in migration actually knows it's dealing with kvm.  So there
should be some indirection - probably through the cpu or the machine
type or something.

Also, this isn't bisectable - you can't make this call in this patch
because you don't define/declare this function until a later patch.


> +                        TARGET_PAGE_SIZE, &bytes_xmit);
> +    if (ret) {
> +        return -1;
> +    }
> +
> +    ram_counters.transferred += bytes_xmit;
> +    ram_counters.normal++;
> +
> +    return 1;
> +}
> +
>  static bool do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block,
>                                   ram_addr_t offset, uint8_t *source_buf)
>  {
> @@ -2450,6 +2485,16 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss,
>          return res;
>      }
>  
> +    /*
> +     * If memory encryption is enabled then use memory encryption APIs
> +     * to write the outgoing buffer to the wire. The encryption APIs
> +     * will take care of accessing the guest memory and re-encrypt it
> +     * for the transport purposes.
> +     */
> +     if (kvm_memcrypt_enabled()) {
> +        return ram_save_encrypted_page(rs, pss, last_stage);
> +     }
> +
>      if (save_compress_page(rs, block, offset)) {
>          return 1;
>      }
> @@ -4271,7 +4316,8 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>          }
>  
>          if (flags & (RAM_SAVE_FLAG_ZERO | RAM_SAVE_FLAG_PAGE |
> -                     RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
> +                     RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE |
> +                     RAM_SAVE_FLAG_ENCRYPTED_PAGE)) {
>              RAMBlock *block = ram_block_from_stream(f, flags);
>  
>              /*
> @@ -4391,6 +4437,12 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>                  break;
>              }
>              break;
> +        case RAM_SAVE_FLAG_ENCRYPTED_PAGE:
> +            if (kvm_memcrypt_load_incoming_page(f, host)) {
> +                    error_report("Failed to encrypted incoming data");

'Failed to *load* encrypted page' ?

> +                    ret = -EINVAL;

Do you want to actually return an error code here from
kvm_memcrypt_load_incoming_page, so we can keep hold of whether
it was something like a simple network error for the file stream
or something more complex.

Dave

> +            }
> +            break;
>          case RAM_SAVE_FLAG_EOS:
>              /* normal exit */
>              multifd_recv_sync_main();
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK