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

From: Paulo de Rezende Pinatti <ppinatti(a)linux.ibm.com&gt; 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 Signed-off-by: Paulo de Rezende Pinatti <ppinatti(a)linux.ibm.com&gt; Reviewed-by: Bjoern Walk <bwalk(a)linux.ibm.com&gt; Reviewed-by: Boris Fiuczynski <fiuczy(a)linux.ibm.com&gt; --- 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();