KVM: x86: avoid vmalloc(0) in the KVM_SET_CPUID
This causes an ugly dmesg splat. Beautified syzkaller testcase:
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/kvm.h>
long r[8];
int main()
{
struct kvm_cpuid2 c = { 0 };
r[2] = open("/dev/kvm", O_RDWR);
r[3] = ioctl(r[2], KVM_CREATE_VM, 0);
r[4] = ioctl(r[3], KVM_CREATE_VCPU, 0x8);
r[7] = ioctl(r[4], KVM_SET_CPUID, &c);
return 0;
}
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 769af90..7597b42 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -181,19 +181,22 @@
struct kvm_cpuid_entry __user *entries)
{
int r, i;
- struct kvm_cpuid_entry *cpuid_entries;
+ struct kvm_cpuid_entry *cpuid_entries = NULL;
r = -E2BIG;
if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
goto out;
r = -ENOMEM;
- cpuid_entries = vmalloc(sizeof(struct kvm_cpuid_entry) * cpuid->nent);
- if (!cpuid_entries)
- goto out;
- r = -EFAULT;
- if (copy_from_user(cpuid_entries, entries,
- cpuid->nent * sizeof(struct kvm_cpuid_entry)))
- goto out_free;
+ if (cpuid->nent) {
+ cpuid_entries = vmalloc(sizeof(struct kvm_cpuid_entry) *
+ cpuid->nent);
+ if (!cpuid_entries)
+ goto out;
+ r = -EFAULT;
+ if (copy_from_user(cpuid_entries, entries,
+ cpuid->nent * sizeof(struct kvm_cpuid_entry)))
+ goto out;
+ }
for (i = 0; i < cpuid->nent; i++) {
vcpu->arch.cpuid_entries[i].function = cpuid_entries[i].function;
vcpu->arch.cpuid_entries[i].eax = cpuid_entries[i].eax;
@@ -212,9 +215,8 @@
kvm_x86_ops->cpuid_update(vcpu);
r = kvm_update_cpuid(vcpu);
-out_free:
- vfree(cpuid_entries);
out:
+ vfree(cpuid_entries);
return r;
}