[edk2-devel] [PATCH v2 15/15] OvfmPkg/VmgExitLib: Validate #VC MMIO is to un-encrypted memory
Laszlo Ersek
lersek at redhat.com
Thu Jan 7 17:27:47 UTC 2021
On 01/06/21 22:21, Lendacky, Thomas wrote:
> From: Tom Lendacky <thomas.lendacky at amd.com>
>
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3108
>
> 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>
> Acked-by: Laszlo Ersek <lersek at redhat.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
> ---
> OvmfPkg/AmdSev/AmdSevX64.dsc | 1 +
> OvmfPkg/OvmfPkgX64.dsc | 1 +
> OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf | 2 +-
> OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf | 2 +
> OvmfPkg/Library/VmgExitLib/VmgExitLib.inf | 2 +
> OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 81 ++++++++++++++++++++
> 6 files changed, 88 insertions(+), 1 deletion(-)
Looks OK, thanks.
Laszlo
> diff --git a/OvmfPkg/AmdSev/AmdSevX64.dsc b/OvmfPkg/AmdSev/AmdSevX64.dsc
> index c4d93f39b9f1..dad8635c3388 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/SecMemEncryptSevLib.inf
>
> [LibraryClasses.common.PEI_CORE]
> HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
> index bfa9dd7cac1f..70ff2bcf2342 100644
> --- a/OvmfPkg/OvmfPkgX64.dsc
> +++ b/OvmfPkg/OvmfPkgX64.dsc
> @@ -266,6 +266,7 @@ [LibraryClasses.common.SEC]
> CpuExceptionHandlerLib|UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf
> !endif
> VmgExitLib|OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
> + MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/SecMemEncryptSevLib.inf
>
> [LibraryClasses.common.PEI_CORE]
> HobLib|MdePkg/Library/PeiHobLib/PeiHobLib.inf
> diff --git a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
> index 8e3b8ddd5a95..f2e162d68076 100644
> --- a/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf
> +++ b/OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.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..e6f6ea7972fd 100644
> --- a/OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
> +++ b/OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf
> @@ -35,6 +35,8 @@ [LibraryClasses]
> BaseLib
> BaseMemoryLib
> DebugLib
> + LocalApicLib
> + 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
>
> 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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