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From: "Laszlo Ersek" <lersek@redhat.com>
To: devel@edk2.groups.io, thomas.lendacky@amd.com
Cc: Jordan Justen <jordan.l.justen@intel.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Michael D Kinney <michael.d.kinney@intel.com>,
	Liming Gao <liming.gao@intel.com>,
	Eric Dong <eric.dong@intel.com>, Ray Ni <ray.ni@intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [edk2-devel] [RFC PATCH v3 32/43] OvmfPkg/QemuFlashFvbServicesRuntimeDxe: Bypass flash detection with SEV-ES is enabled
Date: Thu, 21 Nov 2019 13:31:50 +0100	[thread overview]
Message-ID: <9a6a012c-9bdd-b3cb-65b3-79fda0158e88@redhat.com> (raw)
In-Reply-To: <c5640ef08609ec41192daf619a7048592135eaa3.1574280425.git.thomas.lendacky@amd.com>

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.lendacky@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 <lersek@redhat.com>

Thanks
Laszlo


  reply	other threads:[~2019-11-21 12:32 UTC|newest]

Thread overview: 82+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-20 20:06 [RFC PATCH v3 00/43] SEV-ES guest support Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 01/43] MdePkg: Create PCDs to be used in support of SEV-ES Lendacky, Thomas
2019-12-12  6:53   ` Ni, Ray
2019-12-12 20:48     ` Lendacky, Thomas
2019-12-13  1:21       ` Ni, Ray
2019-11-20 20:06 ` [RFC PATCH v3 02/43] MdePkg: Add the MSR definition for the GHCB register Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 03/43] MdePkg: Add a structure definition for the GHCB Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 04/43] MdeModulePkg/DxeIplPeim: Support GHCB pages when creating page tables Lendacky, Thomas
2019-12-12  6:53   ` [edk2-devel] " Ni, Ray
2019-12-12 20:58     ` Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 05/43] MdePkg/BaseLib: Add support for the XGETBV instruction Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 06/43] MdePkg/BaseLib: Add support for the VMGEXIT instruction Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 07/43] UefiCpuPkg: Implement library support for VMGEXIT Lendacky, Thomas
2019-11-21 11:15   ` [edk2-devel] " Laszlo Ersek
2019-11-21 16:48     ` Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 08/43] UefiCpuPkg/CpuExceptionHandler: Add base support for the #VC exception Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 09/43] UefiCpuPkg/CpuExceptionHandler: Add support for IOIO_PROT NAE events Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 10/43] UefiCpuPkg/CpuExceptionHandler: Support string IO " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 11/43] UefiCpuPkg/CpuExceptionHandler: Add support for CPUID " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 12/43] UefiCpuPkg/CpuExceptionHandler: Add support for MSR_PROT " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 13/43] UefiCpuPkg/CpuExceptionHandler: Add support for NPF NAE events (MMIO) Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 14/43] UefiCpuPkg/CpuExceptionHandler: Add support for WBINVD NAE events Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 15/43] UefiCpuPkg/CpuExceptionHandler: Add support for RDTSC " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 16/43] UefiCpuPkg/CpuExceptionHandler: Add support for RDPMC " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 17/43] UefiCpuPkg/CpuExceptionHandler: Add support for INVD " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 18/43] UefiCpuPkg/CpuExceptionHandler: Add support for VMMCALL " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 19/43] UefiCpuPkg/CpuExceptionHandler: Add support for RDTSCP " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 20/43] UefiCpuPkg/CpuExceptionHandler: Add support for MONITOR/MONITORX " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 21/43] UefiCpuPkg/CpuExceptionHandler: Add support for MWAIT/MWAITX " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 22/43] UefiCpuPkg/CpuExceptionHandler: Add support for DR7 Read/Write " Lendacky, Thomas
2019-12-12  6:53   ` Ni, Ray
2019-12-12 20:39     ` Lendacky, Thomas
2019-12-12  6:53   ` Ni, Ray
2019-12-12 20:27     ` Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 23/43] OvmfPkg/MemEncryptSevLib: Add an SEV-ES guest indicator function Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 24/43] OvmfPkg: Add support to perform SEV-ES initialization Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 25/43] OvmfPkg/ResetVector: Add support for a 32-bit SEV check Lendacky, Thomas
2019-11-21 11:02   ` [edk2-devel] " Laszlo Ersek
2019-11-20 20:06 ` [RFC PATCH v3 26/43] OvmfPkg: Create a GHCB page for use during Sec phase Lendacky, Thomas
2019-11-21 11:29   ` [edk2-devel] " Laszlo Ersek
2019-11-20 20:06 ` [RFC PATCH v3 27/43] OvmfPkg/PlatformPei: Reserve GHCB-related areas if S3 is supported Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 28/43] OvmfPkg: Create GHCB pages for use during Pei and Dxe phase Lendacky, Thomas
2019-12-12  6:54   ` Ni, Ray
2019-12-12 21:03     ` Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 29/43] OvmfPkg/PlatformPei: Move early GDT into ram when SEV-ES is enabled Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 30/43] OvmfPkg/Sec: Add #VC exception handling for Sec phase Lendacky, Thomas
2019-11-21 12:06   ` [edk2-devel] " Laszlo Ersek
2019-11-21 20:46     ` Lendacky, Thomas
2019-11-22 12:52       ` Laszlo Ersek
2019-11-22 16:30         ` Lendacky, Thomas
2019-11-22 21:10           ` Laszlo Ersek
2019-11-22 22:48             ` Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 31/43] OvmfPkg/Sec: Enable cache early to speed up booting Lendacky, Thomas
2019-11-21 12:08   ` [edk2-devel] " Laszlo Ersek
2019-11-20 20:06 ` [RFC PATCH v3 32/43] OvmfPkg/QemuFlashFvbServicesRuntimeDxe: Bypass flash detection with SEV-ES is enabled Lendacky, Thomas
2019-11-21 12:31   ` Laszlo Ersek [this message]
2019-11-21 21:11     ` [edk2-devel] " Lendacky, Thomas
2019-11-22 12:20       ` Laszlo Ersek
2019-11-20 20:06 ` [RFC PATCH v3 33/43] MdeModulePkg: Reserve a 16-bit protected mode code segment descriptor Lendacky, Thomas
2019-12-12  6:57   ` Ni, Ray
2019-12-12 21:19     ` [edk2-devel] " Lendacky, Thomas
2019-12-13  1:20       ` Ni, Ray
2019-11-20 20:06 ` [RFC PATCH v3 34/43] UefiCpuPkg: Add " Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 35/43] UefiCpuPkg/MpInitLib: Add a CPU MP data flag to indicate if SEV-ES is enabled Lendacky, Thomas
2019-12-12  7:01   ` Ni, Ray
2019-12-12 21:21     ` Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 36/43] UefiCpuPkg: Allow AP booting under SEV-ES Lendacky, Thomas
2019-11-20 20:06 ` [RFC PATCH v3 37/43] OvmfPkg: Reserve a page in memory for the SEV-ES AP reset vector Lendacky, Thomas
2019-11-21 19:27   ` [edk2-devel] " Laszlo Ersek
2019-11-21 22:49     ` Lendacky, Thomas
2019-11-22 16:06       ` Laszlo Ersek
2019-11-22 16:40         ` Lendacky, Thomas
2019-11-20 20:07 ` [RFC PATCH v3 38/43] OvmfPkg: Move the GHCB allocations into reserved memory Lendacky, Thomas
2019-11-20 20:07 ` [RFC PATCH v3 39/43] MdePkg: Add a finalization function to the CPU protocol Lendacky, Thomas
2019-11-20 21:32 ` [RFC PATCH v3 40/43] UefiCpuPkg/MpInitLib: Add MP finalization interface to MpInitLib Lendacky, Thomas
2019-11-20 21:32 ` [RFC PATCH v3 41/43] UefiCpuPkg/MpInitLib: Prepare SEV-ES guest APs for OS use Lendacky, Thomas
2019-11-20 21:32 ` [RFC PATCH v3 42/43] UefiCpuPkg/CpuDxe: Provide an DXE MP finalization routine to support SEV-ES Lendacky, Thomas
2019-11-20 21:32 ` [RFC PATCH v3 43/43] MdeModulePkg/DxeCore: Perform the CPU protocol finalization support Lendacky, Thomas
2019-11-21  1:53 ` [edk2-devel] [RFC PATCH v3 00/43] SEV-ES guest support Nate DeSimone
2019-11-21 15:50   ` Lendacky, Thomas
2019-11-21  9:45 ` Laszlo Ersek
2019-11-21  9:48   ` Laszlo Ersek

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