[PATCH 3/6] qemu: check if AMD secure guest support is enabled

[Brijesh Singh]

Thanks for the patch Paulo, Few comments.

On 5/11/20 11:41 AM, Boris Fiuczynski wrote:
> From: Paulo de Rezende Pinatti <ppinatti at linux.ibm.com>
>
> Implement secure guest check for AMD SEV (Secure Encrypted
> Virtualization) in order to invalidate the qemu capabilities
> cache in case the availability of the feature changed.
>
> For AMD SEV the verification consists of:
> - checking if /sys/module/kvm_amd/parameters/sev contains the
> value '1': meaning SEV is enabled in the host kernel;
> - checking if the kernel cmdline contains 'mem_encrypt=on': meaning
> SME memory encryption feature on the host is enabled


In addition to the kernel module parameter, we probably also need to
check whether QEMU supports the feature. e.g, what if user has newer
kernel but older qemu. e.g kernel > 4.18 but Qemu < 2.12.  To check the
SEV feature support, we should verify the following conditions:

1) check kernel module parameter is set

2) check if /dev/sev device exist (aka firmware is detected)

3) Check if Qemu supports SEV feature (maybe we can detect the existence
of the query-sev QMP command or detect Qemu version >= 2.12)

thanks

> Signed-off-by: Paulo de Rezende Pinatti <ppinatti at linux.ibm.com>
> Reviewed-by: Bjoern Walk <bwalk at linux.ibm.com>
> Reviewed-by: Boris Fiuczynski <fiuczy at linux.ibm.com>
> ---
>  docs/kbase/launch_security_sev.rst |  2 +-
>  src/qemu/qemu_capabilities.c       | 27 +++++++++++++++++++++++++++
>  2 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/docs/kbase/launch_security_sev.rst b/docs/kbase/launch_security_sev.rst
> index 65f258587d..fa602c7432 100644
> --- a/docs/kbase/launch_security_sev.rst
> +++ b/docs/kbase/launch_security_sev.rst
> @@ -109,7 +109,7 @@ following:
>       </features>
>     </domainCapabilities>
>  
> -Note that if libvirt was already installed and libvirtd running before
> +Note that if libvirt (<6.4.0) was already installed and libvirtd running before
>  enabling SEV in the kernel followed by the host reboot you need to force
>  libvirtd to re-probe both the host and QEMU capabilities. First stop
>  libvirtd:
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index 2874bb1e7c..6cf926d52d 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -4604,6 +4604,31 @@ virQEMUCapsKVMSupportsSecureGuestS390(void)
>  }
>  
>  
> +/*
> + * Check whether AMD Secure Encrypted Virtualization (x86) is enabled
> + */
> +static bool
> +virQEMUCapsKVMSupportsSecureGuestAMD(void)
> +{
> +    g_autofree char *cmdline = NULL;
> +    g_autofree char *modValue = NULL;
> +    static const char *kValues[] = {"on"};
> +
> +    if (virFileReadValueString(&modValue, "/sys/module/kvm_amd/parameters/sev") < 0)
> +        return false;
> +    if (modValue[0] != '1')
> +        return false;
> +    if (virFileReadValueString(&cmdline, "/proc/cmdline") < 0)
> +        return false;
> +    if (virKernelCmdlineMatchParam(cmdline, "mem_encrypt", kValues,
> +                                   G_N_ELEMENTS(kValues),
> +                                   VIR_KERNEL_CMDLINE_FLAGS_SEARCH_LAST |
> +                                   VIR_KERNEL_CMDLINE_FLAGS_CMP_EQ))
> +        return true;
> +    return false;
> +}
> +
> +
>  /*
>   * Check whether the secure guest functionality is enabled.
>   * See the specific architecture function for details on the verifications made.
> @@ -4615,6 +4640,8 @@ virQEMUCapsKVMSupportsSecureGuest(void)
>  
>      if (ARCH_IS_S390(arch))
>          return virQEMUCapsKVMSupportsSecureGuestS390();
> +    if (ARCH_IS_X86(arch))
> +        return virQEMUCapsKVMSupportsSecureGuestAMD();
>      return false;
>  }
>