437eb3f7a8
BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198 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 VMGEXIT MMIO write support to have the hypervisor perform the write without having to emulate the instruction. Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Laszlo Ersek <lersek@redhat.com> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
65 lines
1.6 KiB
C
65 lines
1.6 KiB
C
/** @file
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Define the module hooks used while probing the QEMU flash device.
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Copyright (C) 2018, Advanced Micro Devices. All rights reserved.
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SPDX-License-Identifier: BSD-2-Clause-Patent
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**/
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#include <Library/BaseMemoryLib.h>
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#include <Library/DebugLib.h>
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#include <Library/PcdLib.h>
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#include <Library/MemEncryptSevLib.h>
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#include "QemuFlash.h"
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VOID
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QemuFlashBeforeProbe (
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IN EFI_PHYSICAL_ADDRESS BaseAddress,
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IN UINTN FdBlockSize,
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IN UINTN FdBlockCount
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)
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{
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EFI_STATUS Status;
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ASSERT (FeaturePcdGet (PcdSmmSmramRequire));
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if (!MemEncryptSevIsEnabled ()) {
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return;
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}
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//
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// When SEV is enabled, AmdSevDxe runs early in DXE phase and clears the
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// C-bit from the NonExistent entry -- which is later split and accommodate
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// the flash MMIO but the driver runs in non SMM context hence it cleared the
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// flash ranges from non SMM page table. When SMM is enabled, the flash
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// services are accessed from the SMM mode hence we explicitly clear the
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// C-bit on flash ranges from SMM page table.
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//
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Status = MemEncryptSevClearPageEncMask (
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0,
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BaseAddress,
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EFI_SIZE_TO_PAGES (FdBlockSize * FdBlockCount),
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FALSE
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);
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ASSERT_EFI_ERROR (Status);
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}
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/**
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Write to QEMU Flash
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@param[in] Ptr Pointer to the location to write.
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@param[in] Value The value to write.
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**/
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VOID
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QemuFlashPtrWrite (
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IN volatile UINT8 *Ptr,
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IN UINT8 Value
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)
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{
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*Ptr = Value;
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}
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