Re: [PATCH v12 07/46] MdePkg/BaseLib: Add support for the VMGEXIT instruction

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 7/28/20 7:04 AM, Laszlo Ersek wrote:
> On 07/28/20 09:39, Gao, Liming wrote:
>> This error is reported from nasm compiler. My nasm compiler version is
>> 2.11.08. It may be a little old. 2.12 should be fine.

I have 2.13.02.

>>
>> This change also requires to update
>> edk2\BaseTools\Conf\tools_def.template and mention nasm compiler
>> version.
> 
> "tools_def.template" says:
> 
>   NASM 2.10 or later for use with the GCC toolchain family
> 
> Bumping the NASM requirement from 2.10 to 2.12 will rule out:
> 
> - Debian "jessie" (oldoldstable),
> - Ubuntu "xenial" (16.04 LTS),
> - and RHEL7,
> 
> as build hosts.
> 
> Debian "jessie" is no longer supported (LTS ended in June 2020), but
> Ubuntu "xenial" and RHEL7 are still supported by their vendors.
> 
> I seem to recall that it was me to recommend "BITS 64" in front of "rep
> vmmcall" in the IA32 NASM source file:
> 
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> 
> I don't understand why my testing worked back then, and now it doesn't.
> (IOW, I can also reproduce the error that Liming reported!) It's likely
> because I didn't specify the elf32 output format back then.
> 
> Indeed: the following command fails:
> 
>> "nasm" \
>>   -I"$WORKSPACE"/MdePkg/Library/BaseLib/Ia32/ \
>>   -I"$WORKSPACE"/MdePkg/Library/BaseLib/Ia32/ \
>>   -I"$WORKSPACE"/MdePkg/Library/BaseLib/ \
>>   -I"$WORKSPACE"/Build/OvmfIa32/NOOPT_GCC48/IA32/MdePkg/Library/BaseLib/BaseLib/DEBUG/ \
>>   -I"$WORKSPACE"/MdePkg/ \
>>   -I"$WORKSPACE"/MdePkg/Include/ \
>>   -I"$WORKSPACE"/MdePkg/Test/UnitTest/Include/ \
>>   -I"$WORKSPACE"/MdePkg/Include/Ia32/ \
>>   -f elf32 \
>>   -o "$WORKSPACE"/Build/OvmfIa32/NOOPT_GCC48/IA32/MdePkg/Library/BaseLib/BaseLib/OUTPUT/Ia32/VmgExit.obj \
>>   "$WORKSPACE"/Build/OvmfIa32/NOOPT_GCC48/IA32/MdePkg/Library/BaseLib/BaseLib/OUTPUT/Ia32/VmgExit.iii
> 
> but if I remove "-f elf32", it completes fine. :(

With version 2.13.02, I can successfully build with '-f elf32', so it
seems to be version related.

> 
> The AMD manual says about VMGEXIT:
> 
>> The VMGEXIT opcode is only valid within a guest when run with SEV-ES
>> mode active. If the guest is not run with SEV-ES mode active, the
>> VMGEXIT opcode will be treated as a VMMCALL opcode and will behave
>> exactly like a VMMCALL.
> 
> VMGEXIT is a SEV-ES-only form of guest-host communication. SEV-ES mode
> depends on SEV. A SEV guest can only interact with the host (= decrypt
> its pages for the host to access) if the guest is executing in long
> mode.
> 
> So does it even make sense to *attempt* implementing AsmVmgExit()
> "correctly" for IA32?

We are only enabling SEV-ES support for X64, so this is a valid point. It
would be very hard to enable the Ia32X64 combination (because of how long
it takes to get into long mode) and impossible for the Ia32 alone.

> 
> I don't want to complicate the build dependencies in this series
> further, so I won't suggest that we simply *not* implement AsmVmgExit()
> for IA32 at all. (Purely from a BaseLib perspective, this would be a
> valid approach, but then call sites would have to be *build-time*
> restricted to X64 too. The call sites *are* already restricted to X64,
> AIUI, but that happens at runtime (= dynamic checks), not at build
> time.)
> 
> So here's what I suggest: implement AsmVmgExit() for IA32 in the C
> language, namely as a call to CpuBreakpoint().

IIUC, create a VmgExit.c file in MdePkg/Library/BaseLib/Ia32/ that doesn't
actually encode the VMGEXIT instruction, just calls CpuBreakpoint(), e.g.:

  VOID
  EFIAPI
  AsmVmgExit (
    VOID
    )
  {
    CpuBreakpoint();
  }


The other alternative is to use a DB-encoded instruction, though I know
that isn't the most popular approach.

The BITS 64 method to generate the instruction bytes is also used in
OvmfPkg/ResetVector/Ia32/PageTables64.asm, but that file is only included
when ARCH_X64 is defined, so there shouldn't be an issue there, plus the
nasm file format is bin (-f bin).

Thanks,
Tom

> 
> I wouldn't like to tighten the NASM version requirement for *all* of
> edk2, for the sake of building a BaseLib primitive for IA32 that we
> never *call* on IA32.
> 
> Thanks,
> Laszlo
> 
>>
>> Thanks
>> Liming
>> -----Original Message-----
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>> Sent: 2020t7\b28å 12:08
>> To: Gao, Liming <liming.gao@intel.com>; devel@edk2.groups.io
>> Cc: Brijesh Singh <brijesh.singh@amd.com>; Ard Biesheuvel <ard.biesheuvel@arm.com>; Dong, Eric <eric.dong@intel.com>; Justen, Jordan L <jordan.l.justen@intel.com>; Laszlo Ersek <lersek@redhat.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Ni, Ray <ray.ni@intel.com>
>> Subject: Re: [PATCH v12 07/46] MdePkg/BaseLib: Add support for the VMGEXIT instruction
>>
>> On 7/27/20 8:34 PM, Gao, Liming wrote:
>>> Tom:
>>
>> Hi Liming,
>>
>>>    I meet with GCC failure on this patch. Can you help check it? If nasm doesn't support the vmmcall instruction in 32-bit mode, you have to use inline assembly to support it.
>>
>> What version of GCC are you using. I was able to successfully build the
>> Ia32 version with my GCC level. The Ia32 version uses a trick to do switch to 64-bit just to encode the instruction. Looks like that doesn't work with your version of GCC.
>>
>> I can probably switch to defining the instruction as bytes. Let me look into that and possibly send you a patch to test.
>>
>> Thanks,
>> Tom
>>
>>>
>>> Edk2/Build/IntelFsp2Pkg/DEBUG_GCC5/IA32/MdePkg/Library/BaseLib/BaseLib
>>> /OUTPUT/Ia32/VmgExit.iii:33: error: elf32 output format does not
>>> support 64-bit code
>>> GNUmakefile:741: recipe for target
>>>
>>> Thanks
>>> Liming
>>> -----Original Message-----
>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>> Sent: 2020t7\b27å 23:26
>>> To: devel@edk2.groups.io
>>> Cc: Brijesh Singh <brijesh.singh@amd.com>; Ard Biesheuvel
>>> <ard.biesheuvel@arm.com>; Dong, Eric <eric.dong@intel.com>; Justen,
>>> Jordan L <jordan.l.justen@intel.com>; Laszlo Ersek
>>> <lersek@redhat.com>; Gao, Liming <liming.gao@intel.com>; Kinney,
>>> Michael D <michael.d.kinney@intel.com>; Ni, Ray <ray.ni@intel.com>
>>> Subject: [PATCH v12 07/46] MdePkg/BaseLib: Add support for the VMGEXIT
>>> instruction
>>>
>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>
>>> BZ:
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugz
>>> illa.tianocore.org%2Fshow_bug.cgi%3Fid%3D2198&amp;data=02%7C01%7Cthoma
>>> s.lendacky%40amd.com%7C77c8250cd9e14f2929a008d832965726%7C3dd8961fe488
>>> 4e608e11a82d994e183d%7C0%7C0%7C637314968570901400&amp;sdata=6zqseI3tVm
>>> aw351w9mfEymMnDcjDzjvcBrhARU6r3Ho%3D&amp;reserved=0
>>>
>>> VMGEXIT is a new instruction used for Hypervisor/Guest communication when running as an SEV-ES guest. A VMGEXIT will cause an automatic exit (AE) to occur, resulting in a #VMEXIT with an exit code value of 0x403.
>>>
>>> Provide the necessary support to execute the VMGEXIT instruction, which is "rep; vmmcall".
>>>
>>> Cc: Michael D Kinney <michael.d.kinney@intel.com>
>>> Cc: Liming Gao <liming.gao@intel.com>
>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>> ---
>>>   MdePkg/Library/BaseLib/BaseLib.inf       |  2 ++
>>>   MdePkg/Include/Library/BaseLib.h         | 14 +++++++++
>>>   MdePkg/Library/BaseLib/Ia32/VmgExit.nasm | 37 ++++++++++++++++++++++++  MdePkg/Library/BaseLib/X64/VmgExit.nasm  | 32 ++++++++++++++++++++
>>>   4 files changed, 85 insertions(+)
>>>   create mode 100644 MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
>>>   create mode 100644 MdePkg/Library/BaseLib/X64/VmgExit.nasm
>>>
>>> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf
>>> b/MdePkg/Library/BaseLib/BaseLib.inf
>>> index 3b93b5db8d24..3b85c56c3c03 100644
>>> --- a/MdePkg/Library/BaseLib/BaseLib.inf
>>> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
>>> @@ -184,6 +184,7 @@ [Sources.Ia32]
>>>     Ia32/DisableCache.nasm| GCC
>>>     Ia32/RdRand.nasm
>>>     Ia32/XGetBv.nasm
>>> +  Ia32/VmgExit.nasm
>>>
>>>     Ia32/DivS64x64Remainder.c
>>>     Ia32/InternalSwitchStack.c | MSFT
>>> @@ -317,6 +318,7 @@ [Sources.X64]
>>>     X64/DisablePaging64.nasm
>>>     X64/RdRand.nasm
>>>     X64/XGetBv.nasm
>>> +  X64/VmgExit.nasm
>>>     ChkStkGcc.c  | GCC
>>>
>>>   [Sources.EBC]
>>> diff --git a/MdePkg/Include/Library/BaseLib.h
>>> b/MdePkg/Include/Library/BaseLib.h
>>> index 7edf0051a0a0..04fb329eaabb 100644
>>> --- a/MdePkg/Include/Library/BaseLib.h
>>> +++ b/MdePkg/Include/Library/BaseLib.h
>>> @@ -7848,6 +7848,20 @@ AsmXGetBv (
>>>     );
>>>
>>>
>>> +/**
>>> +  Executes a VMGEXIT instruction (VMMCALL with a REP prefix)
>>> +
>>> +  Executes a VMGEXIT instruction. This function is only available on
>>> + IA-32 and  x64.
>>> +
>>> +**/
>>> +VOID
>>> +EFIAPI
>>> +AsmVmgExit (
>>> +  VOID
>>> +  );
>>> +
>>> +
>>>   /**
>>>     Patch the immediate operand of an IA32 or X64 instruction such that the byte,
>>>     word, dword or qword operand is encoded at the end of the
>>> instruction's diff --git a/MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
>>> b/MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
>>> new file mode 100644
>>> index 000000000000..a4b37385cc7a
>>> --- /dev/null
>>> +++ b/MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
>>> @@ -0,0 +1,37 @@
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +;
>>> +; Copyright (C) 2020, Advanced Micro Devices, Inc. All rights
>>> +reserved.<BR> ; SPDX-License-Identifier: BSD-2-Clause-Patent ; ;
>>> +Module
>>> +Name:
>>> +;
>>> +;   VmgExit.Asm
>>> +;
>>> +; Abstract:
>>> +;
>>> +;   AsmVmgExit function
>>> +;
>>> +; Notes:
>>> +;
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +
>>> +    SECTION .text
>>> +
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +; VOID
>>> +; EFIAPI
>>> +; AsmVmgExit (
>>> +;   VOID
>>> +;   );
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +global ASM_PFX(AsmVmgExit)
>>> +ASM_PFX(AsmVmgExit):
>>> +;
>>> +; NASM doesn't support the vmmcall instruction in 32-bit mode, so
>>> +work around ; this by temporarily switching to 64-bit mode.
>>> +;
>>> +BITS    64
>>> +    rep     vmmcall
>>> +BITS    32
>>> +    ret
>>> +
>>> diff --git a/MdePkg/Library/BaseLib/X64/VmgExit.nasm
>>> b/MdePkg/Library/BaseLib/X64/VmgExit.nasm
>>> new file mode 100644
>>> index 000000000000..26f034593c67
>>> --- /dev/null
>>> +++ b/MdePkg/Library/BaseLib/X64/VmgExit.nasm
>>> @@ -0,0 +1,32 @@
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +;
>>> +; Copyright (C) 2020, Advanced Micro Devices, Inc. All rights
>>> +reserved.<BR> ; SPDX-License-Identifier: BSD-2-Clause-Patent ; ;
>>> +Module
>>> +Name:
>>> +;
>>> +;   VmgExit.Asm
>>> +;
>>> +; Abstract:
>>> +;
>>> +;   AsmVmgExit function
>>> +;
>>> +; Notes:
>>> +;
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +
>>> +    DEFAULT REL
>>> +    SECTION .text
>>> +
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +; VOID
>>> +; EFIAPI
>>> +; AsmVmgExit (
>>> +;   VOID
>>> +;   );
>>> +;--------------------------------------------------------------------
>>> +--
>>> +--------
>>> +global ASM_PFX(AsmVmgExit)
>>> +ASM_PFX(AsmVmgExit):
>>> +    rep     vmmcall
>>> +    ret
>>> +
>>> --
>>> 2.27.0
>>>
>>
>