On 11/20/19 21:06, Lendacky, Thomas wrote: > The flash detection routine will attempt to determine how the flash > device behaves (e.g. ROM, RAM, Flash). But when SEV-ES is enabled and > the flash device behaves as a ROM device (meaning it is marked read-only > by the hypervisor), this check may result in an infinite nested page fault > because of the attempted write. Since the instruction cannot be emulated > when SEV-ES is enabled, the RIP is never advanced, resulting in repeated > nested page faults. > > When SEV-ES is enabled, exit the flash detection early and assume that > the FD behaves as Flash. This will result in QemuFlashWrite() being called > to store EFI variables, which will also result in an infinite nested page > fault when the write is performed. In this case, update QemuFlashWrite() > to use the VmgMmioWrite function from the VmgExitLib library to have the > hypervisor perform the write without having to emulate the instruction.
(1) Please include the Bugzilla link in the commit message: https://bugzilla.tianocore.org/show_bug.cgi?id=2198 > > Signed-off-by: Tom Lendacky <thomas.lenda...@amd.com> > --- > OvmfPkg/OvmfPkgIa32.dsc | 1 + > OvmfPkg/OvmfPkgIa32X64.dsc | 1 + > OvmfPkg/OvmfPkgX64.dsc | 1 + > .../FvbServicesRuntimeDxe.inf | 2 + > .../QemuFlash.c | 38 +++++++++++++++++-- > 5 files changed, 40 insertions(+), 3 deletions(-) > > diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc > index 56670eefde6b..ff2814c6246e 100644 > --- a/OvmfPkg/OvmfPkgIa32.dsc > +++ b/OvmfPkg/OvmfPkgIa32.dsc > @@ -320,6 +320,7 @@ [LibraryClasses.common.DXE_RUNTIME_DRIVER] > BaseCryptLib|CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf > PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf > QemuFwCfgS3Lib|OvmfPkg/Library/QemuFwCfgS3Lib/DxeQemuFwCfgS3LibFwCfg.inf > + VmgExitLib|UefiCpuPkg/Library/VmgExitLib/VmgExitLib.inf > > [LibraryClasses.common.UEFI_DRIVER] > PcdLib|MdePkg/Library/DxePcdLib/DxePcdLib.inf > diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc > index 9897e6889573..212952cfaacd 100644 > --- a/OvmfPkg/OvmfPkgIa32X64.dsc > +++ b/OvmfPkg/OvmfPkgIa32X64.dsc > @@ -325,6 +325,7 @@ [LibraryClasses.common.DXE_RUNTIME_DRIVER] > BaseCryptLib|CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf > PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf > QemuFwCfgS3Lib|OvmfPkg/Library/QemuFwCfgS3Lib/DxeQemuFwCfgS3LibFwCfg.inf > + VmgExitLib|UefiCpuPkg/Library/VmgExitLib/VmgExitLib.inf > > [LibraryClasses.common.UEFI_DRIVER] > PcdLib|MdePkg/Library/DxePcdLib/DxePcdLib.inf > diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc > index 59c4f9207fc3..8331fc0b663e 100644 > --- a/OvmfPkg/OvmfPkgX64.dsc > +++ b/OvmfPkg/OvmfPkgX64.dsc > @@ -325,6 +325,7 @@ [LibraryClasses.common.DXE_RUNTIME_DRIVER] > BaseCryptLib|CryptoPkg/Library/BaseCryptLib/RuntimeCryptLib.inf > PciLib|OvmfPkg/Library/DxePciLibI440FxQ35/DxePciLibI440FxQ35.inf > QemuFwCfgS3Lib|OvmfPkg/Library/QemuFwCfgS3Lib/DxeQemuFwCfgS3LibFwCfg.inf > + VmgExitLib|UefiCpuPkg/Library/VmgExitLib/VmgExitLib.inf > > [LibraryClasses.common.UEFI_DRIVER] > PcdLib|MdePkg/Library/DxePcdLib/DxePcdLib.inf > diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf > b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf > index ca6326e833ed..0b7741ac07f8 100644 > --- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf > +++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf > @@ -38,6 +38,7 @@ [Sources] > [Packages] > MdePkg/MdePkg.dec > MdeModulePkg/MdeModulePkg.dec > + UefiCpuPkg/UefiCpuPkg.dec > OvmfPkg/OvmfPkg.dec > > [LibraryClasses] > @@ -52,6 +53,7 @@ [LibraryClasses] > UefiBootServicesTableLib > UefiDriverEntryPoint > UefiRuntimeLib > + VmgExitLib > > [Guids] > gEfiEventVirtualAddressChangeGuid # ALWAYS_CONSUMED These hunks look good. > diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c > b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c > index c81c58972bf2..4f3bf690fcad 100644 > --- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c > +++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/QemuFlash.c > @@ -9,7 +9,9 @@ > > #include <Library/BaseMemoryLib.h> > #include <Library/DebugLib.h> > +#include <Library/MemEncryptSevLib.h> > #include <Library/PcdLib.h> > +#include <Library/VmgExitLib.h> > > #include "QemuFlash.h" > > @@ -80,6 +82,20 @@ QemuFlashDetected ( > > DEBUG ((EFI_D_INFO, "QEMU Flash: Attempting flash detection at %p\n", > Ptr)); > > + if (MemEncryptSevEsIsEnabled()) { > + // > + // When SEV-ES is enabled, the check below can result in an infinite > + // loop with respect to a nested page fault. When the FD behaves as > + // a ROM, the nested page table entry is read-only. The check below (2) I suggest a slight change to the wording above. Please replace when the FD behaves as a ROM with when the memslot is mapped read-only (It's OK to make qemu / kvm references in this code: the name of the file includes "Qemu".) > + // will cause a nested page fault that cannot be emulated, causing > + // the instruction to retried over and over. For SEV-ES, assume that > + // the FD does not behave as FLASH. (3) I would recommend For SEV-ES, acknowledge that the FD appears as ROM and not as FLASH, but report FLASH anyway. > + // > + DEBUG ((DEBUG_INFO, > + "QEMU Flash: SEV-ES enabled, assuming FD behaves as FLASH\n")); > + return TRUE; > + } > + > OriginalUint8 = *Ptr; > *Ptr = CLEAR_STATUS_CMD; > ProbeUint8 = *Ptr; > @@ -147,6 +163,21 @@ QemuFlashRead ( > } > > > +STATIC > +VOID > +QemuFlashPtrWrite ( > + IN volatile UINT8 *Ptr, > + IN UINT8 Value > + ) > +{ > + if (MemEncryptSevEsIsEnabled()) { > + VmgMmioWrite ((UINT8 *) Ptr, &Value, 1); > + } else { > + *Ptr = Value; > + } > +} > + > + > /** > Write to QEMU Flash > (4) This change will break the "FvbServicesSmm.inf" build of this module. (Because, you have -- correctly -- added the VmgExitLib class to "FvbServicesRuntimeDxe.inf" only.) Please: - create two implementations of the QemuFlashPtrWrite() function, one in "QemuFlashDxe.c", and another in "QemuFlashSmm.c". - the former should be the function shown above, the latter should only perform the direct assignment. - the '#include <Library/VmgExitLib.h>' directive should also be moved to "QemuFlashDxe.c". - the prototype for QemuFlashPtrWrite() should be added to "QemuFlash.h" please. > @@ -181,8 +212,9 @@ QemuFlashWrite ( > // > Ptr = QemuFlashPtr (Lba, Offset); > for (Loop = 0; Loop < *NumBytes; Loop++) { > - *Ptr = WRITE_BYTE_CMD; > - *Ptr = Buffer[Loop]; > + QemuFlashPtrWrite (Ptr, WRITE_BYTE_CMD); > + QemuFlashPtrWrite (Ptr, Buffer[Loop]); > + > Ptr++; > } > > @@ -190,7 +222,7 @@ QemuFlashWrite ( > // Restore flash to read mode > // > if (*NumBytes > 0) { > - *(Ptr - 1) = READ_ARRAY_CMD; > + QemuFlashPtrWrite (Ptr - 1, READ_ARRAY_CMD); > } > > return EFI_SUCCESS; > With (1) and (4) fixed, and with (2) and (3) optionally fixed (i.e., if you agree): Reviewed-by: Laszlo Ersek <ler...@redhat.com> Thanks Laszlo -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. 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