Re: [Qemu-devel] [RFC PATCH v1 16/22] i386: pc: load OS images at fixed location in SEV-enabled guest

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 13, 2016 at 10:49:29AM -0400, Brijesh Singh wrote:
> Typically linux kernel, initrd and cmdline are build and loaded
> into guest memory through linux optionrom. The linux optionrom is
> probed and executed by SeaBIOS. This method will not work for
> SEV-enabled guest.
> 
> In SEV-enabled guest all the code and data must be copied using SEV
> launch command prior to starting the guest (i.e before first vmrun).
> The data copied using SEV launch command will be encrypted using guest
> owner's key. This patch loads kernel, initrd and cmdline blobs at fixed
> location into guest memory and builds etc/sev_cfg config file. The cfg
> file provide the below structure
> 
> struct sev_cfg {
> 	u32 kernel_addr, initrd_addr, cmdline_addr;
> 	u32 kernel_size, initrd_size, cmdline_size;
> }
> 
> The config file can be used by SeaBIOS to locate OS images into guest
> RAM and build linux boot entry code.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

I don't think we want to give users this kind of
control over how we manage memory internally
for what is essentially a debugging feature at this point.

Isn't there a way to first launch guest, and then have it
encrypt itself once it's running?

If not, I guess it's not too bad if -kernel does not
work with sev debug feature - just load kernel from disk.


> ---
>  hw/i386/pc.c |   94 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 93 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 1471df4..f2c7472 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -104,6 +104,15 @@ static struct e820_entry *e820_table;
>  static unsigned e820_entries;
>  struct hpet_fw_config hpet_cfg = {.count = UINT8_MAX};
>  
> +struct sev_cfg_data {
> +    uint32_t kernel_addr;
> +    uint32_t initrd_addr;
> +    uint32_t cmdline_addr;
> +    uint32_t kernel_size;
> +    uint32_t initrd_size;
> +    uint32_t cmdline_size;
> +} QEMU_PACKED __attribute((__aligned__(4)));
> +
>  void gsi_handler(void *opaque, int n, int level)
>  {
>      GSIState *s = opaque;
> @@ -824,6 +833,86 @@ struct setup_data {
>      uint8_t data[0];
>  } __attribute__((packed));
>  
> +#define round_up(x, align) ((x + align) & ~(align - 1))
> +
> +static void sev_load_file_fixed(const char *filename, int start,
> +                                int *end, int *sz)
> +{
> +    FILE *f;
> +    int sz_aligned, ret;
> +    char *data;
> +
> +    f = fopen(filename, "rb");
> +    if (!f) {
> +        fprintf(stderr, "qemu: could not load '%s': %s\n",
> +                filename, strerror(errno));
> +        exit(1);
> +    }
> +
> +    /* SEV update commands needs 16-byte aligned length */
> +    *sz = get_file_size(f);
> +    sz_aligned = round_up(*sz, 16);
> +    data = g_malloc(sz_aligned);
> +    ret = fread(data, 1, *sz, f);
> +    if (ret != *sz) {
> +        fprintf(stderr, "qemu: failed to read %d bytes from %s\n",
> +                *sz, filename);
> +        exit(1);
> +    }
> +    rom_add_blob_fixed(filename, data, sz_aligned, start);
> +    *end = start + sz_aligned;
> +    fclose(f);
> +    g_free(data);
> +}
> +
> +/* load kernel, initrd and cmdline blobs at fixed location into guest
> + * memory and generate etc/sev config file.
> + */
> +static void sev_load_linux(PCMachineState *pcms,
> +                           FWCfgState *fw_cfg)
> +{
> +    FILE *f;
> +    int cmdline_size, kernel_size, initrd_size;
> +    int initrd_addr, kernel_addr, cmdline_addr, end;
> +    MachineState *machine = MACHINE(pcms);
> +    const char *kernel_cmdline = machine->kernel_cmdline;
> +    struct sev_cfg_data *sev_cfg;
> +    char *cmdline_string;
> +
> +    /* load kernel command line string */
> +    cmdline_addr = 0x1000000;
> +    cmdline_size = round_up(strlen(kernel_cmdline), 16);
> +    cmdline_string = g_malloc(cmdline_size);
> +    strncpy(cmdline_string, kernel_cmdline, strlen(kernel_cmdline));
> +    rom_add_blob_fixed("cmdline", cmdline_string, cmdline_size, cmdline_addr);
> +    g_free(cmdline_string);
> +
> +    /* load linux kernel */
> +    kernel_addr = cmdline_addr + cmdline_size;
> +    sev_load_file_fixed(machine->kernel_filename, kernel_addr,
> +            &initrd_addr, &kernel_size);
> +
> +    /* load initrd */
> +    f = fopen(machine->initrd_filename, "rb");
> +    if (f) {
> +        sev_load_file_fixed(machine->initrd_filename, initrd_addr,
> +                &end, &initrd_size);
> +    } else {
> +        initrd_addr = 0;
> +        initrd_size = 0;
> +    }
> +
> +    sev_cfg = g_malloc0(sizeof(*sev_cfg));
> +    sev_cfg->kernel_addr = kernel_addr;
> +    sev_cfg->initrd_addr = initrd_addr;
> +    sev_cfg->cmdline_addr = cmdline_addr;
> +    sev_cfg->kernel_size = kernel_size;
> +    sev_cfg->initrd_size = initrd_size;
> +    sev_cfg->cmdline_size = cmdline_size;
> +
> +    fw_cfg_add_file(fw_cfg, "etc/sev_cfg", sev_cfg, sizeof(*sev_cfg));
> +}
> +
>  static void load_linux(PCMachineState *pcms,
>                         FWCfgState *fw_cfg)
>  {
> @@ -1471,7 +1560,10 @@ void pc_memory_init(PCMachineState *pcms,
>      }
>  
>      if (linux_boot) {
> -        load_linux(pcms, fw_cfg);
> +        if (kvm_sev_enabled())
> +            sev_load_linux(pcms, fw_cfg);
> +        else
> +            load_linux(pcms, fw_cfg);
>      }
>  
>      for (i = 0; i < nb_option_roms; i++) {