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UefiCpuPkg, OvmfPkg: Disable interrupts when using the GHCB

Browse Source 
BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3008

The QemuFlashPtrWrite() flash services runtime uses the GHCB and VmgExit()
directly to perform the flash write when running as an SEV-ES guest. If an
interrupt arrives between VmgInit() and VmgExit(), the Dr7 read in the
interrupt handler will generate a #VC, which can overwrite information in
the GHCB that QemuFlashPtrWrite() has set. This has been seen with the
timer interrupt firing and the CpuExceptionHandlerLib library code,
UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/
  Xcode5ExceptionHandlerAsm.nasm and
  ExceptionHandlerAsm.nasm
reading the Dr7 register while QemuFlashPtrWrite() is using the GHCB. In
general, it is necessary to protect the GHCB whenever it is used, not just
in QemuFlashPtrWrite().

Disable interrupts around the usage of the GHCB by modifying the VmgInit()
and VmgDone() interfaces:
- VmgInit() will take an extra parameter that is a pointer to a BOOLEAN
  that will hold the interrupt state at the time of invocation. VmgInit()
  will get and save this interrupt state before updating the GHCB.
- VmgDone() will take an extra parameter that is used to indicate whether
  interrupts are to be (re)enabled. Before exiting, VmgDone() will enable
  interrupts if that is requested.

Fixes: 437eb3f7a8db7681afe0e6064d3a8edb12abb766
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Acked-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <c326a4fd78253f784b42eb317589176cf7d8592a.1604685192.git.thomas.lendacky@amd.com>
This commit is contained in:
Tom Lendacky 2020-11-06 11:53:12 -06:00 committed by mergify[bot]
parent fdce11226c
commit 1b0db1ec87
7 changed files with 55 additions and 25 deletions
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26
OvmfPkg/Library/VmgExitLib/VmgExitLib.c
View File

@ -132,15 +132,27 @@ VmgExit (
Performs the necessary steps in preparation for invoking VMGEXIT. Must be
called before setting any fields within the GHCB.
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] InterruptState A pointer to hold the current interrupt
state, used for restoring in VmgDone ()
**/
VOID
EFIAPI
VmgInit (
IN OUT GHCB *Ghcb
IN OUT GHCB *Ghcb,
IN OUT BOOLEAN *InterruptState
)
{
//
// Be sure that an interrupt can't cause a #VC while the GHCB is
// being used.
//
*InterruptState = GetInterruptState ();
if (*InterruptState) {
DisableInterrupts ();
}
SetMem (&Ghcb->SaveArea, sizeof (Ghcb->SaveArea), 0);
}
@ -150,15 +162,21 @@ VmgInit (
Performs the necessary steps to cleanup after invoking VMGEXIT. Must be
called after obtaining needed fields within the GHCB.
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] Ghcb A pointer to the GHCB
@param[in] InterruptState An indicator to conditionally (re)enable
interrupts
**/
VOID
EFIAPI
VmgDone (
IN OUT GHCB *Ghcb
IN OUT GHCB *Ghcb,
IN BOOLEAN InterruptState
)
{
if (InterruptState) {
EnableInterrupts ();
}
}
/**

5
OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
View File

@ -1568,6 +1568,7 @@ VmgExitHandleVc (
SEV_ES_INSTRUCTION_DATA InstructionData;
UINT64 ExitCode, Status;
EFI_STATUS VcRet;
BOOLEAN InterruptState;
VcRet = EFI_SUCCESS;
@ -1578,7 +1579,7 @@ VmgExitHandleVc (
Regs = SystemContext.SystemContextX64;
Ghcb = Msr.Ghcb;
VmgInit (Ghcb);
VmgInit (Ghcb, &InterruptState);
ExitCode = Regs->ExceptionData;
switch (ExitCode) {
@ -1662,7 +1663,7 @@ VmgExitHandleVc (
VcRet = EFI_PROTOCOL_ERROR;
}
VmgDone (Ghcb);
VmgDone (Ghcb, InterruptState);
return VcRet;
}

5
OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlashDxe.c
View File

@ -52,6 +52,7 @@ QemuFlashPtrWrite (
if (MemEncryptSevEsIsEnabled ()) {
MSR_SEV_ES_GHCB_REGISTER Msr;
GHCB *Ghcb;
BOOLEAN InterruptState;
Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
Ghcb = Msr.Ghcb;
@ -63,12 +64,12 @@ QemuFlashPtrWrite (
// #VC exception. Instead, use the the VMGEXIT MMIO write support directly
// to perform the update.
//
VmgInit (Ghcb);
VmgInit (Ghcb, &InterruptState);
Ghcb->SharedBuffer[0] = Value;
Ghcb->SaveArea.SwScratch = (UINT64) (UINTN) Ghcb->SharedBuffer;
VmgSetOffsetValid (Ghcb, GhcbSwScratch);
VmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, (UINT64) (UINTN) Ptr, 1);
VmgDone (Ghcb);
VmgDone (Ghcb, InterruptState);
} else {
*Ptr = Value;
}

14
UefiCpuPkg/Include/Library/VmgExitLib.h
View File

@ -50,13 +50,16 @@ VmgExit (
Performs the necessary steps in preparation for invoking VMGEXIT. Must be
called before setting any fields within the GHCB.
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] InterruptState A pointer to hold the current interrupt
state, used for restoring in VmgDone ()
**/
VOID
EFIAPI
VmgInit (
IN OUT GHCB *Ghcb
IN OUT GHCB *Ghcb,
IN OUT BOOLEAN *InterruptState
);
/**
@ -65,13 +68,16 @@ VmgInit (
Performs the necessary steps to cleanup after invoking VMGEXIT. Must be
called after obtaining needed fields within the GHCB.
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] Ghcb A pointer to the GHCB
@param[in] InterruptState An indicator to conditionally (re)enable
interrupts
**/
VOID
EFIAPI
VmgDone (
IN OUT GHCB *Ghcb
IN OUT GHCB *Ghcb,
IN BOOLEAN InterruptState
);
/**

5
UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
View File

@ -171,6 +171,7 @@ GetSevEsAPMemory (
EFI_PHYSICAL_ADDRESS StartAddress;
MSR_SEV_ES_GHCB_REGISTER Msr;
GHCB *Ghcb;
BOOLEAN InterruptState;
//
// Allocate 1 page for AP jump table page
@ -192,9 +193,9 @@ GetSevEsAPMemory (
Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
Ghcb = Msr.Ghcb;
VmgInit (Ghcb);
VmgInit (Ghcb, &InterruptState);
VmgExit (Ghcb, SVM_EXIT_AP_JUMP_TABLE, 0, (UINT64) (UINTN) StartAddress);
VmgDone (Ghcb);
VmgDone (Ghcb, InterruptState);
return (UINTN) StartAddress;
}

7
UefiCpuPkg/Library/MpInitLib/MpLib.c
View File

@ -884,6 +884,7 @@ ApWakeupFunction (
GHCB *Ghcb;
UINT64 Status;
BOOLEAN DoDecrement;
BOOLEAN InterruptState;
DoDecrement = (BOOLEAN) (CpuMpData->InitFlag == ApInitConfig);
@ -891,7 +892,7 @@ ApWakeupFunction (
Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
Ghcb = Msr.Ghcb;
VmgInit (Ghcb);
VmgInit (Ghcb, &InterruptState);
if (DoDecrement) {
DoDecrement = FALSE;
@ -905,11 +906,11 @@ ApWakeupFunction (
Status = VmgExit (Ghcb, SVM_EXIT_AP_RESET_HOLD, 0, 0);
if ((Status == 0) && (Ghcb->SaveArea.SwExitInfo2 != 0)) {
VmgDone (Ghcb);
VmgDone (Ghcb, InterruptState);
break;
}
VmgDone (Ghcb);
VmgDone (Ghcb, InterruptState);
}
//

18
UefiCpuPkg/Library/VmgExitLibNull/VmgExitLibNull.c
View File

@ -57,15 +57,16 @@ VmgExit (
Performs the necessary steps in preparation for invoking VMGEXIT. Must be
called before setting any fields within the GHCB.
The base library function does nothing.
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] InterruptState A pointer to hold the current interrupt
state, used for restoring in VmgDone ()
**/
VOID
EFIAPI
VmgInit (
IN OUT GHCB *Ghcb
IN OUT GHCB *Ghcb,
IN OUT BOOLEAN *InterruptState
)
{
}
@ -76,15 +77,16 @@ VmgInit (
Performs the necessary steps to cleanup after invoking VMGEXIT. Must be
called after obtaining needed fields within the GHCB.
The base library function does nothing.
@param[in, out] Ghcb A pointer to the GHCB
@param[in, out] Ghcb A pointer to the GHCB
@param[in] InterruptState An indicator to conditionally (re)enable
interrupts
**/
VOID
EFIAPI
VmgDone (
IN OUT GHCB *Ghcb
IN OUT GHCB *Ghcb,
IN BOOLEAN InterruptState
)
{
}