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Emulate IA32_BIOS_SIGN_ID read

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This commit is contained in:
Satoshi Tanda
2020-02-23 13:12:33 -08:00
parent b9b638d32b
commit fa47889170
4 changed files with 89 additions and 26 deletions
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37
Sources/HostMain.c
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@@ -47,6 +47,12 @@ typedef struct _INITIAL_HYPERVISOR_STACK
/*!
@brief Handles VM-exit due to execution of the RDMSR and WRMSR instruction.
@details Accessing MSR can results in #GP(0) that would have been handled by
the guest. However, in this context, this results in host exception leading
to the panic (See HandleHostException). For graceful handling, the handler
can check the exception is #GP(0) caused by RDMSR or WRMSR, and if this
is the case, inject it to the guest.
@param[in,out] GuestContext - A pointer to the guest context.
@param[in] OperationType - The type of the operation.
@@ -64,18 +70,35 @@ HandleMsrAccess (
msr = (IA32_MSR_ADDRESS)GuestContext->StackBasedRegisters->Rcx;
if (OperationType == OperationRead)
{
//
// Performs the same read on behalf of the guest.
//
value = __readmsr(msr);
switch (msr)
{
case IA32_BIOS_SIGN_ID:
//
// Linux reads this MSR during boot and may attempt to update BIOS
// microcode. Returning the greater value than the value the kernel
// wishes prevent it from attempt to update microcode. APs will enter
// infinite INIT-SIPI loop if this is not done.
//
// "The VMM may wish to prevent a guest from loading a microcode
// update (...). To prevent microcode update loading, the VMM may
// return a microcode update signature value greater than the value
// of IA32_BIOS_SIGN_ID MSR. A well behaved guest will not attempt
// to load an older microcode update."
// See: 32.4.2 Late Load of Microcode Updates
//
value = MAXUINT64;
break;
default:
value = __readmsr(msr);
break;
}
GuestContext->StackBasedRegisters->Rax = value & MAXUINT32;
GuestContext->StackBasedRegisters->Rdx = (value >> 32) & MAXUINT32;
}
else
{
//
// Performs the same write on behalf of the guest.
//
value = (GuestContext->StackBasedRegisters->Rax & MAXUINT32) |
((GuestContext->StackBasedRegisters->Rdx & MAXUINT32) << 32);
__writemsr(msr, value);