8000 kvm: enable CPUID faulting on all VCPUs by copybara-service[bot] · Pull Request #11492 · google/gvisor · GitHub
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kvm: enable CPUID faulting on all VCPUs #11492

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Merged
merged 1 commit into from
Mar 4, 2025
Merged

kvm: enable CPUID faulting on all VCPUs #11492

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21 changes: 0 additions & 21 deletions pkg/ring0/kernel_amd64.go
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Original file line number Diff line number Diff line change
Expand Up @@ -315,27 +315,6 @@ func startGo(c *CPU) {
wrmsr(_MSR_CSTAR, kernelFunc(addrOfSysenter()))
}

// SetCPUIDFaulting sets CPUID faulting per the boolean value.
//
// True is returned if faulting could be set.
//
//go:nosplit
func SetCPUIDFaulting(on bool) bool {
// Per the SDM (Vol 3, Table 2-43), PLATFORM_INFO bit 31 denotes support
// for CPUID faulting, and we enable and disable via the MISC_FEATURES MSR.
if rdmsr(_MSR_PLATFORM_INFO)&_PLATFORM_INFO_CPUID_FAULT != 0 {
features := rdmsr(_MSR_MISC_FEATURES)
if on {
features |= _MISC_FEATURE_CPUID_TRAP
} else {
features &^= _MISC_FEATURE_CPUID_TRAP
}
wrmsr(_MSR_MISC_FEATURES, features)
return true // Setting successful.
}
return false
}

// ReadCR2 reads the current CR2 value.
//
//go:nosplit
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14 changes: 4 additions & 10 deletions pkg/ring0/x86.go
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Expand Up @@ -52,16 +52,10 @@ const (
_EFER_LMA = 0x400
_EFER_NX = 0x800

_MSR_STAR = 0xc0000081
_MSR_LSTAR = 0xc0000082
_MSR_CSTAR = 0xc0000083
_MSR_SYSCALL_MASK = 0xc0000084
_MSR_PLATFORM_INFO = 0xce
_MSR_MISC_FEATURES = 0x140

_PLATFORM_INFO_CPUID_FAULT = 1 << 31

_MISC_FEATURE_CPUID_TRAP = 0x1
_MSR_STAR = 0xc0000081
_MSR_LSTAR = 0xc0000082
_MSR_CSTAR = 0xc0000083
_MSR_SYSCALL_MASK = 0xc0000084
)

const (
Expand Down
38 changes: 20 additions & 18 deletions pkg/sentry/platform/kvm/machine_amd64.go
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Original file line number Diff line number Diff line change
Expand Up @@ -22,17 +22,18 @@ import (
"math/big"
"reflect"
"runtime"
"runtime/debug"

"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/cpuid"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/hostsyscall"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/ring0"
"gvisor.dev/gvisor/pkg/ring0/pagetables"
"gvisor.dev/gvisor/pkg/sentry/platform"
ktime "gvisor.dev/gvisor/pkg/sentry/time"
"gvisor.dev/gvisor/pkg/sync"
)

// initArchState initializes architecture-specific state.
Expand All @@ -54,22 +55,6 @@ func (m *machine) initArchState() error {
}
m.mu.Unlock()

c := m.Get()
defer m.Put(c)
// Enable CPUID faulting, if possible. Note that this also serves as a
// basic platform sanity tests, since we will enter guest mode for the
// first time here. The recovery is necessary, since if we fail to read
// the platform info register, we will retry to host mode and
// ultimately need to handle a segmentation fault.
old := debug.SetPanicOnFault(true)
defer func() {
recover()
debug.SetPanicOnFault(old)
}()

bluepill(c)
ring0.SetCPUIDFaulting(true)

return nil
}

Expand Down Expand Up @@ -97,6 +82,8 @@ const (
poolPCIDs = 8
)

var cpuidFaultingWarnOnce sync.Once

// initArchState initializes architecture-specific state.
func (c *vCPU) initArchState() error {
var (
Expand Down Expand Up @@ -158,7 +145,22 @@ func (c *vCPU) initArchState() error {
}

// Set the time offset to the host native time.
return c.setSystemTime()
if err := c.setSystemTime(); err != nil {
return err
}

// Try to enable CPUID faulting. This is required to handle app CPUID
// correctly, since we always pass the CPUID returned by
// KVM_GET_SUPPORTED_CPUID to KVM_SET_CPUID2. Note that while hardware
// support for CPUID faulting is inconsistent, KVM always supports it after
// db2336a80489e ("KVM: x86: virtualize cpuid faulting"), Linux 4.12+.
if err := c.enableCPUIDFaulting(); err != nil {
cpuidFaultingWarnOnce.Do(func() {
log.Warningf("Application CPUID will be incorrect: %v", err)
})
}

return nil
}

// bitsForScaling returns the bits available for storing the fraction component
Expand Down
20 changes: 20 additions & 0 deletions pkg/sentry/platform/kvm/machine_amd64_unsafe.go
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Expand Up @@ -140,6 +140,26 @@ func (c *vCPU) setTSC(value uint64) error {
return nil
}

func (c *vCPU) enableCPUIDFaulting() error {
const (
_MSR_MISC_FEATURES_ENABLE = 0x140
_MSR_MISC_FEATURES_ENABLES_CPUID_FAULT = 1 << 0
)
registers := modelControlRegisters{
nmsrs: 1,
}
registers.entries[0].index = _MSR_MISC_FEATURES_ENABLE
registers.entries[0].data = _MSR_MISC_FEATURES_ENABLES_CPUID_FAULT
if errno := hostsyscall.RawSyscallErrno(
unix.SYS_IOCTL,
uintptr(c.fd),
KVM_SET_MSRS,
uintptr(unsafe.Pointer(&registers))); errno != 0 {
return fmt.Errorf("error enabling CPUID faulting: %v", errno)
}
return nil
}

// setUserRegisters sets user registers in the vCPU.
//
//go:nosplit
Expand Down
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