Re: [edk2-devel] [PATCH] UefiCpuPkg/MpInitLib: Add check for CR3/GDT/IDT.

["Laszlo Ersek" <lersek@redhat.com>]

Hi Eric,

On 09/02/20 02:43, Dong, Eric wrote:
> AP needs to run from real mode to 32bit mode to LONG mode. Page table
> (pointed by CR3) and GDT are necessary to set up to correct value when
> CPU execution mode is switched to LONG mode.
> AP uses the same location page table (CR3) and GDT as what BSP uses.
> But when the page table or GDT is above 4GB, it's impossible for CPU
> to use because GDTR.base and CR3 are 32bits before switching to LONG
> mode.
> This patch adds check for the CR3, GDT.Base and IDT.Base to not above
> 32 bits restriction.
> 
> Signed-off-by: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/DxeMpLib.c |   8 +-
>  UefiCpuPkg/Library/MpInitLib/MpLib.c    | 108 +++++++++++++++++++-----
>  UefiCpuPkg/Library/MpInitLib/MpLib.h    |   6 +-
>  3 files changed, 97 insertions(+), 25 deletions(-)

(1) This is not for edk2-stable202008, correct?


(2) If I understand correctly, this patch does not solve the problem
when any one of the IDT, GDT, and CR3, are out of 32-bit address space.
Instead, the patch makes the failure symptoms more graceful.

Is that correct?

If so, can you explain in the commit message what happens without the
patch, versus with the patch, when the IDT / GDT / CR3 are out of 32-bit
address space?

Like, if we abandon MpInitChangeApLoopCallback() mid-way, then (AIUI)
the AP "pen" (HLT loop) will not be relocated to reserved memory at
ExitBootServces(). I don't think that simply giving up can end well for
the OS!


(3) Can you remind us in the commit message where the IDT / GDT / page
tables are actually allocated? That is, can you please name the
component that is usually responsible for keeping the allocations in the
32-bit address space?

And once we know where the IDT / GDT / page tables come from --
shouldn't we rather modify those modules, to allocate IDT / GDT / page
tables in the 32-bit address space?

More below:

> diff --git a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
> index 2c00d72dde..27f12a75a8 100644
> --- a/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/DxeMpLib.c
> @@ -393,13 +393,19 @@ MpInitChangeApLoopCallback (
>    )
>  {
>    CPU_MP_DATA               *CpuMpData;
> +  EFI_STATUS                Status;
>  
>    CpuMpData = GetCpuMpData ();
>    CpuMpData->PmCodeSegment = GetProtectedModeCS ();
>    CpuMpData->Pm16CodeSegment = GetProtectedMode16CS ();
>    CpuMpData->ApLoopMode = PcdGet8 (PcdCpuApLoopMode);
>    mNumberToFinish = CpuMpData->CpuCount - 1;
> -  WakeUpAP (CpuMpData, TRUE, 0, RelocateApLoop, NULL, TRUE);
> +  Status = WakeUpAP (CpuMpData, TRUE, 0, RelocateApLoop, NULL, TRUE);
> +  if (EFI_ERROR (Status)) {
> +    DEBUG ((DEBUG_ERROR, "ERROR :: %a() Change Ap Loop Mode failed!\n", __FUNCTION__));
> +    return;
> +  }
> +
>    while (mNumberToFinish > 0) {
>      CpuPause ();
>    }
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index 07426274f6..21b17a7b40 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -470,7 +470,7 @@ GetProcessorNumber (
>  
>    @return  CPU count detected
>  **/
> -UINTN
> +EFI_STATUS
>  CollectProcessorCount (
>    IN CPU_MP_DATA         *CpuMpData
>    )
> @@ -478,12 +478,17 @@ CollectProcessorCount (
>    UINTN                  Index;
>    CPU_INFO_IN_HOB        *CpuInfoInHob;
>    BOOLEAN                X2Apic;
> +  EFI_STATUS             Status;
>  
>    //
>    // Send 1st broadcast IPI to APs to wakeup APs
>    //
>    CpuMpData->InitFlag = ApInitConfig;
> -  WakeUpAP (CpuMpData, TRUE, 0, NULL, NULL, TRUE);
> +  Status = WakeUpAP (CpuMpData, TRUE, 0, NULL, NULL, TRUE);
> +  if (EFI_ERROR (Status)) {
> +    return Status;
> +  }
> +
>    CpuMpData->InitFlag = ApInitDone;
>    ASSERT (CpuMpData->CpuCount <= PcdGet32 (PcdCpuMaxLogicalProcessorNumber));
>    //
> @@ -520,7 +525,11 @@ CollectProcessorCount (
>      //
>      // Wakeup all APs to enable x2APIC mode
>      //
> -    WakeUpAP (CpuMpData, TRUE, 0, ApFuncEnableX2Apic, NULL, TRUE);
> +    Status = WakeUpAP (CpuMpData, TRUE, 0, ApFuncEnableX2Apic, NULL, TRUE);
> +    if (EFI_ERROR (Status)) {
> +      return Status;
> +    }
> +
>      //
>      // Wait for all known APs finished
>      //
> @@ -546,7 +555,7 @@ CollectProcessorCount (
>  
>    DEBUG ((DEBUG_INFO, "MpInitLib: Find %d processors in system.\n", CpuMpData->CpuCount));
>  
> -  return CpuMpData->CpuCount;
> +  return EFI_SUCCESS;
>  }
>  
>  /**
> @@ -990,7 +999,7 @@ WaitApWakeup (
>    @param[in] CpuMpData          Pointer to CPU MP Data
>  
>  **/
> -VOID
> +EFI_STATUS
>  FillExchangeInfoData (
>    IN CPU_MP_DATA               *CpuMpData
>    )
> @@ -1001,6 +1010,35 @@ FillExchangeInfoData (
>    IA32_CR4                         Cr4;
>  
>    ExchangeInfo                  = CpuMpData->MpCpuExchangeInfo;
> +  ExchangeInfo->Cr3             = AsmReadCr3 ();
> +  if (ExchangeInfo->Cr3 > 0xFFFFFFFF) {
> +    //
> +    // AP needs to run from real mode to 32bit mode to LONG mode. Page table
> +    // (pointed by CR3) and GDT are necessary to set up to correct value when
> +    // CPU execution mode is switched to LONG mode.
> +    // AP uses the same location page table (CR3) and GDT as what BSP uses.
> +    // But when the page table or GDT is above 4GB, it's impossible for CPU
> +    // to use because GDTR.base and CR3 are 32bits before switching to LONG
> +    // mode.
> +    // Here add check for the CR3, GDT.Base and IDT.Base to not above 32 bits
> +    // limitation.
> +    //
> +    return EFI_UNSUPPORTED;
> +  }
> +
> +  //
> +  // Get the BSP's data of GDT and IDT
> +  //
> +  AsmReadGdtr ((IA32_DESCRIPTOR *) &ExchangeInfo->GdtrProfile);
> +  if (ExchangeInfo->GdtrProfile.Base > 0xFFFFFFFF) {
> +    return EFI_UNSUPPORTED;
> +  }
> +
> +  AsmReadIdtr ((IA32_DESCRIPTOR *) &ExchangeInfo->IdtrProfile);
> +  if (ExchangeInfo->IdtrProfile.Base > 0xFFFFFFFF) {
> +    return EFI_UNSUPPORTED;
> +  }
> +
>    ExchangeInfo->Lock            = 0;
>    ExchangeInfo->StackStart      = CpuMpData->Buffer;
>    ExchangeInfo->StackSize       = CpuMpData->CpuApStackSize;

(4) Style: I think we should use

  >= BASE_4GB

rather than

  > 0xFFFFFFFF

(5) Correctness: the conditions above only check the base addresses of
the tables. However I think we should check whether the *last byte* in
each table fits in 32-bits.

(6) How about a different approach: in case we realize the IDT / GDT /
page tables are "out of reach", can we simply copy them under 4GB, and
pass the *copy* to the APs? (I guess this would be difficult with the
page table hierarchy.)

--*--

All in all I'm really surprised (and concerned!) that we need to add an
after-the-fact check for this situation. This situation should never
occur, in my opinion.

Basically the idea seems to be that FillExchangeInfoData() can now fail,
and because of that, WakeUpAP() can now fail too. And we attempt to
propagate that failure out to the callers of WakeUpAP().

But WakeUpAP() is called from *lots* of places, which currently assume
that WakeUpAP() can not fail. I don't think it may even be possible to
cleanly handle WakeUpAP() failure in some of those places. I mentioned
MpInitChangeApLoopCallback() in point (2) above, but
CollectProcessorCount() is a good example too. If
CollectProcessorCount() is abandoned early, then we won't know how many
CPUs are in the system, xAPIC / x2APIC mode will not be set, etc. So
basically MP services in the system will be unusable. I don't think we
should even attempt booting at all, in that case.

I think we should look into point (3) more deeply; that is, figure out
where the page tables / IDT / GDT are allocated in the first place, and
make sure *in those modules* that the allocation is safe.


Hmm wait -- if MpInitLibInitialize() fails (for example because
CollectProcessorCount() fails), then we hit ASSERT_EFI_ERROR()s anyway!
In the following locations:

- InitializeMpSupport() function in "UefiCpuPkg/CpuDxe/CpuMp.c",

- MemoryDiscoveredPpiNotifyCallback() function in
"UefiCpuPkg/CpuMpPei/CpuPaging.c" -- via InitializeCpuMpWorker()

So it seems like this condition is impossible to mitigate, and we're not
going to boot even with this patch (in NOOPT/DEBUG builds) if the
condition occurs (and RELEASE builds will just crash or misbehave badly).

However, in that case, I don't think we should complicate the code with
a bunch of error propagation. We identify the problem in
FillExchangeInfoData(). *If* we cannot fix the agents that are
responsible for the GDT / IDT / page table allocations in the first
place, *then* we should ASSERT() in FillExchangeInfoData() immediately.
It's a serious platform misconfiguration, and we shouldn't even attempt
to continue.

Consider it from the following angle too: if this condition causes
MpInitLibInitialize() to fail, then we'll never reach functions such as
SwitchBSPWorker() and MpInitChangeApLoopCallback() -- so why complicate
them with new branches (that don't do the right thing anyway)?


Is it perhaps the case that the open source code in edk2 *itself* is
safe, but you have some proprietary firmware platforms that use
MpInitLib *but* do not satisfy the 32-bit allocation requirements? How
and where was the problem actually experienced?

Thanks,
Laszlo



> @@ -1009,9 +1047,6 @@ FillExchangeInfoData (
>  
>    ExchangeInfo->CodeSegment     = AsmReadCs ();
>    ExchangeInfo->DataSegment     = AsmReadDs ();
> -
> -  ExchangeInfo->Cr3             = AsmReadCr3 ();
> -
>    ExchangeInfo->CFunction       = (UINTN) ApWakeupFunction;
>    ExchangeInfo->ApIndex         = 0;
>    ExchangeInfo->NumApsExecuting = 0;
> @@ -1037,13 +1072,6 @@ FillExchangeInfoData (
>  
>    ExchangeInfo->SevEsIsEnabled  = CpuMpData->SevEsIsEnabled;
>    ExchangeInfo->GhcbBase        = (UINTN) CpuMpData->GhcbBase;
> -
> -  //
> -  // Get the BSP's data of GDT and IDT
> -  //
> -  AsmReadGdtr ((IA32_DESCRIPTOR *) &ExchangeInfo->GdtrProfile);
> -  AsmReadIdtr ((IA32_DESCRIPTOR *) &ExchangeInfo->IdtrProfile);
> -
>    //
>    // Find a 32-bit code segment
>    //
> @@ -1084,6 +1112,8 @@ FillExchangeInfoData (
>                           (UINT32)ExchangeInfo->ModeOffset -
>                           (UINT32)CpuMpData->AddressMap.ModeTransitionOffset;
>    ExchangeInfo->ModeHighSegment = (UINT16)ExchangeInfo->CodeSegment;
> +
> +  return EFI_SUCCESS;
>  }
>  
>  /**
> @@ -1308,8 +1338,12 @@ SetSevEsJumpTable (
>    @param[in] Procedure          The function to be invoked by AP
>    @param[in] ProcedureArgument  The argument to be passed into AP function
>    @param[in] WakeUpDisabledAps  Whether need to wake up disabled APs in broadcast mode.
> +
> +  @retval EFI_SUCCESS           Wake up the AP success.
> +  @retval EFI_UNSUPPORTED       Invalid CR3, IDT, GDT value caused fail to wake up AP.
> +
>  **/
> -VOID
> +EFI_STATUS
>  WakeUpAP (
>    IN CPU_MP_DATA               *CpuMpData,
>    IN BOOLEAN                   Broadcast,
> @@ -1324,6 +1358,7 @@ WakeUpAP (
>    CPU_AP_DATA                      *CpuData;
>    BOOLEAN                          ResetVectorRequired;
>    CPU_INFO_IN_HOB                  *CpuInfoInHob;
> +  EFI_STATUS                       Status;
>  
>    CpuMpData->FinishedCount = 0;
>    ResetVectorRequired = FALSE;
> @@ -1333,7 +1368,10 @@ WakeUpAP (
>      ResetVectorRequired = TRUE;
>      AllocateResetVector (CpuMpData);
>      AllocateSevEsAPMemory (CpuMpData);
> -    FillExchangeInfoData (CpuMpData);
> +    Status = FillExchangeInfoData (CpuMpData);
> +    if (EFI_ERROR (Status)) {
> +      return Status;
> +    }
>      SaveLocalApicTimerSetting (CpuMpData);
>    }
>  
> @@ -1500,6 +1538,8 @@ WakeUpAP (
>    // S3SmmInitDone Ppi.
>    //
>    CpuMpData->WakeUpByInitSipiSipi = (CpuMpData->ApLoopMode == ApInHltLoop);
> +
> +  return EFI_SUCCESS;
>  }
>  
>  /**
> @@ -1945,6 +1985,7 @@ MpInitLibInitialize (
>    UINTN                    ApResetVectorSize;
>    UINTN                    BackupBufferAddr;
>    UINTN                    ApIdtBase;
> +  EFI_STATUS               Status;
>  
>    OldCpuMpData = GetCpuMpDataFromGuidedHob ();
>    if (OldCpuMpData == NULL) {
> @@ -2067,7 +2108,10 @@ MpInitLibInitialize (
>        //
>        // Wakeup all APs and calculate the processor count in system
>        //
> -      CollectProcessorCount (CpuMpData);
> +      Status = CollectProcessorCount (CpuMpData);
> +      if (EFI_ERROR (Status)) {
> +        return Status;
> +      }
>      }
>    } else {
>      //
> @@ -2118,7 +2162,11 @@ MpInitLibInitialize (
>        //
>        CpuMpData->InitFlag = ApInitReconfig;
>      }
> -    WakeUpAP (CpuMpData, TRUE, 0, ApInitializeSync, CpuMpData, TRUE);
> +    Status = WakeUpAP (CpuMpData, TRUE, 0, ApInitializeSync, CpuMpData, TRUE);
> +    if (EFI_ERROR (Status)) {
> +      return Status;
> +    }
> +
>      //
>      // Wait for all APs finished initialization
>      //
> @@ -2262,6 +2310,7 @@ SwitchBSPWorker (
>    MSR_IA32_APIC_BASE_REGISTER  ApicBaseMsr;
>    BOOLEAN                      OldInterruptState;
>    BOOLEAN                      OldTimerInterruptState;
> +  EFI_STATUS                   Status;
>  
>    //
>    // Save and Disable Local APIC timer interrupt
> @@ -2333,7 +2382,10 @@ SwitchBSPWorker (
>    //
>    // Need to wakeUp AP (future BSP).
>    //
> -  WakeUpAP (CpuMpData, FALSE, ProcessorNumber, FutureBSPProc, CpuMpData, TRUE);
> +  Status = WakeUpAP (CpuMpData, FALSE, ProcessorNumber, FutureBSPProc, CpuMpData, TRUE);
> +  if (EFI_ERROR (Status)) {
> +    return Status;
> +  }
>  
>    AsmExchangeRole (&CpuMpData->BSPInfo, &CpuMpData->APInfo);
>  
> @@ -2669,14 +2721,21 @@ StartupAllCPUsWorker (
>    CpuMpData->WaitEvent     = WaitEvent;
>  
>    if (!SingleThread) {
> -    WakeUpAP (CpuMpData, TRUE, 0, Procedure, ProcedureArgument, FALSE);
> +    Status = WakeUpAP (CpuMpData, TRUE, 0, Procedure, ProcedureArgument, FALSE);
> +    if (EFI_ERROR (Status)) {
> +      return Status;
> +    }
>    } else {
>      for (ProcessorNumber = 0; ProcessorNumber < ProcessorCount; ProcessorNumber++) {
>        if (ProcessorNumber == CallerNumber) {
>          continue;
>        }
>        if (CpuMpData->CpuData[ProcessorNumber].Waiting) {
> -        WakeUpAP (CpuMpData, FALSE, ProcessorNumber, Procedure, ProcedureArgument, TRUE);
> +        Status = WakeUpAP (CpuMpData, FALSE, ProcessorNumber, Procedure, ProcedureArgument, TRUE);
> +        if (EFI_ERROR (Status)) {
> +          return Status;
> +        }
> +
>          break;
>        }
>      }
> @@ -2795,7 +2854,10 @@ StartupThisAPWorker (
>    CpuData->ExpectedTime = CalculateTimeout (TimeoutInMicroseconds, &CpuData->CurrentTime);
>    CpuData->TotalTime    = 0;
>  
> -  WakeUpAP (CpuMpData, FALSE, ProcessorNumber, Procedure, ProcedureArgument, TRUE);
> +  Status = WakeUpAP (CpuMpData, FALSE, ProcessorNumber, Procedure, ProcedureArgument, TRUE);
> +  if (EFI_ERROR (Status)) {
> +    return Status;
> +  }
>  
>    //
>    // If WaitEvent is NULL, execute in blocking mode.
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.h b/UefiCpuPkg/Library/MpInitLib/MpLib.h
> index 02652eaae1..9cf5c0f9b4 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.h
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.h
> @@ -459,8 +459,12 @@ GetSevEsAPMemory (
>    @param[in] Procedure          The function to be invoked by AP
>    @param[in] ProcedureArgument  The argument to be passed into AP function
>    @param[in] WakeUpDisabledAps  Whether need to wake up disabled APs in broadcast mode.
> +
> +  @retval EFI_SUCCESS           Wake up the AP success.
> +  @retval EFI_UNSUPPORTED       Invalid CR3, IDT, GDT value caused fail to wake up AP.
> +
>  **/
> -VOID
> +EFI_STATUS
>  WakeUpAP (
>    IN CPU_MP_DATA               *CpuMpData,
>    IN BOOLEAN                   Broadcast,
>