[edk2-devel] [PATCH 12/12] OvfmPkg/VmgExitLib: Validate #VC MMIO is to un-encrypted memory
Lendacky, Thomas
thomas.lendacky at amd.com
Tue Jan 5 14:45:01 UTC 2021
On 1/5/21 4:28 AM, Laszlo Ersek wrote:
> On 12/15/20 21:51, Lendacky, Thomas wrote:
>> From: Tom Lendacky <thomas.lendacky at amd.com>
>>
>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3108&data=04%7C01%7Cthomas.lendacky%40amd.com%7C4a5d3dd1c25d4935bd6608d8b164b73b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637454393417282277%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=vEIKCoKCg1P46pkl2X0iod8x5I7%2FGyDu9beOoR2Pfww%3D&reserved=0
>>
>> When SEV-ES is active, and MMIO operation will trigger a #VC and the
>> VmgExitLib exception handler will process this MMIO operation.
>>
>> A malicious hypervisor could try to extract information from encrypted
>> memory by setting a reserved bit in the guests nested page tables for
>> a non-MMIO area. This can result in the encrypted data being copied into
>> the GHCB shared buffer area and accessed by the hypervisor.
>>
>> Prevent this by ensuring that the MMIO source/destination is un-encrypted
>> memory. For the APIC register space, access is allowed in general.
>>
>> Cc: Jordan Justen <jordan.l.justen at intel.com>
>> Cc: Laszlo Ersek <lersek at redhat.com>
>> Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
>> Cc: Brijesh Singh <brijesh.singh at amd.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
>> ---
>> OvmfPkg/AmdSev/AmdSevX64.dsc | 1 +
>> OvmfPkg/OvmfPkgX64.dsc | 1 +
>> .../DxeBaseMemEncryptSevLib.inf | 2 +-
>> OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf | 1 +
>> OvmfPkg/Library/VmgExitLib/VmgExitLib.inf | 2 +
>> OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 81 +++++++++++++++++++
>> 6 files changed, 87 insertions(+), 1 deletion(-)
>>
>> diff --git a/OvmfPkg/AmdSev/AmdSevX64.dsc b/OvmfPkg/AmdSev/AmdSevX64.dsc
>> index 3e5a3f648ad5..d0e9d28fc492 100644
>> --- a/OvmfPkg/AmdSev/AmdSevX64.dsc
>> +++ b/OvmfPkg/AmdSev/AmdSevX64.dsc
>> @@ -237,6 +237,7 @@ [LibraryClasses.common.SEC]
>> CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf
>> !endif
>> VmgExitLib|OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
>> + MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/SecBaseMemEncryptSevLib.inf
>>
>> [LibraryClasses.common.PEI_CORE]
>> HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
>> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
>> index 226b576545a9..2a230888c636 100644
>> --- a/OvmfPkg/OvmfPkgX64.dsc
>> +++ b/OvmfPkg/OvmfPkgX64.dsc
>> @@ -265,6 +265,7 @@ [LibraryClasses.common.SEC]
>> CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf
>> !endif
>> VmgExitLib|OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
>> + MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/SecBaseMemEncryptSevLib.inf
>>
>> [LibraryClasses.common.PEI_CORE]
>> HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
>> diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeBaseMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeBaseMemEncryptSevLib.inf
>> index 04728a5dd256..10f794759207 100644
>> --- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeBaseMemEncryptSevLib.inf
>> +++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeBaseMemEncryptSevLib.inf
>> @@ -14,7 +14,7 @@ [Defines]
>> FILE_GUID = c1594631-3888-4be4-949f-9c630dbc842b
>> MODULE_TYPE = BASE
>> VERSION_STRING = 1.0
>> - LIBRARY_CLASS = MemEncryptSevLib|DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER UEFI_DRIVER
>> + LIBRARY_CLASS = MemEncryptSevLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER UEFI_DRIVER
>>
>> #
>> # The following information is for reference only and not required by the build
>> diff --git a/OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf b/OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
>> index df14de3c21bc..9c8de326f3d1 100644
>> --- a/OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
>> +++ b/OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
>> @@ -35,6 +35,7 @@ [LibraryClasses]
>> BaseLib
>> BaseMemoryLib
>> DebugLib
>> + MemEncryptSevLib
>> PcdLib
>>
>> [FixedPcd]
>> diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitLib.inf b/OvmfPkg/Library/VmgExitLib/VmgExitLib.inf
>> index b3c3e56ecff8..c66c68726cdb 100644
>> --- a/OvmfPkg/Library/VmgExitLib/VmgExitLib.inf
>> +++ b/OvmfPkg/Library/VmgExitLib/VmgExitLib.inf
>> @@ -35,4 +35,6 @@ [LibraryClasses]
>> BaseLib
>> BaseMemoryLib
>> DebugLib
>> + LocalApicLib
>> + MemEncryptSevLib
>>
>
> (1) I don't understand why LocalApicLib is added only to
> "VmgExitLib.inf", and not "SecVmgExitLib.inf". The source file
> "VmgExitVcHandler.c" is shared between both INF files, and that file
> gets a GetLocalApicBaseAddress() call below. And, "SecVmgExitLib.inf"
> doesn't list the LocalApicLib class dependency from any earlier patch.
>
> ... Hm, the issue is masked because "OvmfPkg/Sec/SecMain.inf" lists
> LocalApicLib already, so when the SEC module is linked, the LocalApicLib
> dependency is ultimately (independently) noted/satisfied.
>
> But, that doesn't make this omission right; please amend the
> "SecVmgExitLib.inf" file.
Good catch, I'm not sure how I missed that. I'll make that change.
Thanks,
Tom
>
> With that update:
>
> Acked-by: Laszlo Ersek <lersek at redhat.com>
>
> Thanks
> Laszlo
>
>> diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
>> index ce577e4677eb..24259060fd65 100644
>> --- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
>> +++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
>> @@ -9,6 +9,7 @@
>> #include <Base.h>
>> #include <Uefi.h>
>> #include <Library/BaseMemoryLib.h>
>> +#include <Library/LocalApicLib.h>
>> #include <Library/MemEncryptSevLib.h>
>> #include <Library/VmgExitLib.h>
>> #include <Register/Amd/Msr.h>
>> @@ -595,6 +596,61 @@ UnsupportedExit (
>> return Status;
>> }
>>
>> +/**
>> + Validate that the MMIO memory access is not to encrypted memory.
>> +
>> + Examine the pagetable entry for the memory specified. MMIO should not be
>> + performed against encrypted memory. MMIO to the APIC page is always allowed.
>> +
>> + @param[in] Ghcb Pointer to the Guest-Hypervisor Communication Block
>> + @param[in] MemoryAddress Memory address to validate
>> + @param[in] MemoryLength Memory length to validate
>> +
>> + @retval 0 Memory is not encrypted
>> + @return New exception value to propogate
>> +
>> +**/
>> +STATIC
>> +UINT64
>> +ValidateMmioMemory (
>> + IN GHCB *Ghcb,
>> + IN UINTN MemoryAddress,
>> + IN UINTN MemoryLength
>> + )
>> +{
>> + MEM_ENCRYPT_SEV_ADDRESS_RANGE_STATE State;
>> + GHCB_EVENT_INJECTION GpEvent;
>> + UINTN Address;
>> +
>> + //
>> + // Allow APIC accesses (which will have the encryption bit set during
>> + // SEC and PEI phases).
>> + //
>> + Address = MemoryAddress & ~(SIZE_4KB - 1);
>> + if (Address == GetLocalApicBaseAddress ()) {
>> + return 0;
>> + }
>> +
>> + State = MemEncryptSevGetAddressRangeState (
>> + 0,
>> + MemoryAddress,
>> + MemoryLength
>> + );
>> + if (State == MemEncryptSevAddressRangeUnencrypted) {
>> + return 0;
>> + }
>> +
>> + //
>> + // Any state other than unencrypted is an error, issue a #GP.
>> + //
>> + GpEvent.Uint64 = 0;
>> + GpEvent.Elements.Vector = GP_EXCEPTION;
>> + GpEvent.Elements.Type = GHCB_EVENT_INJECTION_TYPE_EXCEPTION;
>> + GpEvent.Elements.Valid = 1;
>> +
>> + return GpEvent.Uint64;
>> +}
>> +
>> /**
>> Handle an MMIO event.
>>
>> @@ -653,6 +709,11 @@ MmioExit (
>> return UnsupportedExit (Ghcb, Regs, InstructionData);
>> }
>>
>> + Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);
>> + if (Status != 0) {
>> + return Status;
>> + }
>> +
>> ExitInfo1 = InstructionData->Ext.RmData;
>> ExitInfo2 = Bytes;
>> CopyMem (Ghcb->SharedBuffer, &InstructionData->Ext.RegData, Bytes);
>> @@ -683,6 +744,11 @@ MmioExit (
>> InstructionData->ImmediateSize = Bytes;
>> InstructionData->End += Bytes;
>>
>> + Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);
>> + if (Status != 0) {
>> + return Status;
>> + }
>> +
>> ExitInfo1 = InstructionData->Ext.RmData;
>> ExitInfo2 = Bytes;
>> CopyMem (Ghcb->SharedBuffer, InstructionData->Immediate, Bytes);
>> @@ -717,6 +783,11 @@ MmioExit (
>> return UnsupportedExit (Ghcb, Regs, InstructionData);
>> }
>>
>> + Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);
>> + if (Status != 0) {
>> + return Status;
>> + }
>> +
>> ExitInfo1 = InstructionData->Ext.RmData;
>> ExitInfo2 = Bytes;
>>
>> @@ -748,6 +819,11 @@ MmioExit (
>> case 0xB7:
>> Bytes = (Bytes != 0) ? Bytes : 2;
>>
>> + Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);
>> + if (Status != 0) {
>> + return Status;
>> + }
>> +
>> ExitInfo1 = InstructionData->Ext.RmData;
>> ExitInfo2 = Bytes;
>>
>> @@ -774,6 +850,11 @@ MmioExit (
>> case 0xBF:
>> Bytes = (Bytes != 0) ? Bytes : 2;
>>
>> + Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);
>> + if (Status != 0) {
>> + return Status;
>> + }
>> +
>> ExitInfo1 = InstructionData->Ext.RmData;
>> ExitInfo2 = Bytes;
>>
>>
>
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