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i386: assert 'cs->kvm_state' is not null 

Coverity reports potential NULL pointer dereference in
get_supported_hv_cpuid_legacy() when 'cs->kvm_state' is NULL. While
'cs->kvm_state' can indeed be NULL in hv_cpuid_get_host(),
kvm_hyperv_expand_features() makes sure that it only happens when
KVM_CAP_SYS_HYPERV_CPUID is supported and KVM_CAP_SYS_HYPERV_CPUID
implies KVM_CAP_HYPERV_CPUID so get_supported_hv_cpuid_legacy() is
never really called. Add asserts to strengthen the protection against
broken KVM behavior.

Coverity: CID 1458243
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210716115852.418293-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2021-07-16 13:58:51 +02:00 committed by Paolo Bonzini
parent 69ea12b19a
commit e4adb09f79
1 changed files with 14 additions and 0 deletions
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14
target/i386/kvm/kvm.c
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@ -974,6 +974,12 @@ static struct kvm_cpuid2 *get_supported_hv_cpuid(CPUState *cs)
do_sys_ioctl =
kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID) > 0;
/*
* Non-empty KVM context is needed when KVM_CAP_SYS_HYPERV_CPUID is
* unsupported, kvm_hyperv_expand_features() checks for that.
*/
assert(do_sys_ioctl || cs->kvm_state);
/*
* When the buffer is too small, KVM_GET_SUPPORTED_HV_CPUID fails with
* -E2BIG, however, it doesn't report back the right size. Keep increasing
@ -1105,6 +1111,14 @@ static uint32_t hv_cpuid_get_host(CPUState *cs, uint32_t func, int reg)
if (kvm_check_extension(kvm_state, KVM_CAP_HYPERV_CPUID) > 0) {
cpuid = get_supported_hv_cpuid(cs);
} else {
/*
* 'cs->kvm_state' may be NULL when Hyper-V features are expanded
* before KVM context is created but this is only done when
* KVM_CAP_SYS_HYPERV_CPUID is supported and it implies
* KVM_CAP_HYPERV_CPUID.
*/
assert(cs->kvm_state);
cpuid = get_supported_hv_cpuid_legacy(cs);
}
hv_cpuid_cache = cpuid;