Re: [PATCH 4/4] OvmfPkg/QemuVideoDxe: Update QemuVideoDxe driver to bypass NULL pointer detection if enabled.

["Wang, Jian J" <jian.j.wang@intel.com>]

It’s an implementation limitation. All page attributes will be filtered out before calling CPU arch protocol to update the attributes (Gcd.c).

From: Yao, Jiewen
Sent: Thursday, September 14, 2017 4:38 PM
To: Laszlo Ersek <lersek@redhat.com>; Wang, Jian J <jian.j.wang@intel.com>
Cc: Dong, Eric <eric.dong@intel.com>; Justen, Jordan L <jordan.l.justen@intel.com>; edk2-devel@lists.01.org; Wolman, Ayellet <ayellet.wolman@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Zeng, Star <star.zeng@intel.com>
Subject: RE: [edk2] [PATCH 4/4] OvmfPkg/QemuVideoDxe: Update QemuVideoDxe driver to bypass NULL pointer detection if enabled.

HI
I wonder if it is spec limitation or implementation limitation.

If it is implementation limitation, we can enhance the DxeCore to allow it.

Thank you
Yao Jiewen

From: Laszlo Ersek [mailto:lersek@redhat.com]
Sent: Thursday, September 14, 2017 4:30 PM
To: Wang, Jian J <jian.j.wang@intel.com<mailto:jian.j.wang@intel.com>>
Cc: Dong, Eric <eric.dong@intel.com<mailto:eric.dong@intel.com>>; Justen, Jordan L <jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>; edk2-devel@lists.01.org<mailto:edk2-devel@lists.01.org>; Yao, Jiewen <jiewen.yao@intel.com<mailto:jiewen.yao@intel.com>>; Wolman, Ayellet <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>; Kinney, Michael D <michael.d.kinney@intel.com<mailto:michael.d.kinney@intel.com>>; Zeng, Star <star.zeng@intel.com<mailto:star.zeng@intel.com>>
Subject: Re: [edk2] [PATCH 4/4] OvmfPkg/QemuVideoDxe: Update QemuVideoDxe driver to bypass NULL pointer detection if enabled.

On 09/14/17 05:17, Wang, Jian J wrote:
> For the use of arch protocol, there's one thing I mentioned is not
> accurate. I actually tried gDS->SetMemorySpaceAttributes() but it
> cannot change page attributes. That's why I have to turn to cpu arch
> protocol.
Thank you for the explanation.

In that case, we cannot avoid violating the PI spec. I agree we can
break the spec if it happens for security purposes, but in that case, I
believe that hiding the implementation behind a library class is
mandatory. Viewed from the spec side, accessing the CPU Arch protocol is
a hack, and so it should not be spread to the source code of several
driver modules.

Thank you,
Laszlo


>
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Wang, Jian J
> Sent: Thursday, September 14, 2017 9:17 AM
> To: Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>
> Cc: Dong, Eric <eric.dong@intel.com<mailto:eric.dong@intel.com>>; Justen, Jordan L <jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>; edk2-devel@lists.01.org<mailto:edk2-devel@lists.01.org>; Yao, Jiewen <jiewen.yao@intel.com<mailto:jiewen.yao@intel.com>>; Wolman, Ayellet <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>; Kinney, Michael D <michael.d.kinney@intel.com<mailto:michael.d.kinney@intel.com>>; Zeng, Star <star.zeng@intel.com<mailto:star.zeng@intel.com>>
> Subject: Re: [edk2] [PATCH 4/4] OvmfPkg/QemuVideoDxe: Update QemuVideoDxe driver to bypass NULL pointer detection if enabled.
>
> Thanks for the comments and good advices. Sorry the format issues.
> This is my first patch for this project. Too many details for me to get
> familiar with.
>
> (1) Sure.
> (2) I'll change that.
> (3) I'll use the tool to ensure the patch format.
> (4) I'll remove the ',' in name
> (5) I'll add more description about it.
> (6) You're right. I should use SetMemorySpaceAttributes() of DXE service
>      instead. The only reason I didn't do it is that I found
>       GetMemorySpaceDescriptor() doesn't return the same information
>      which SetMemorySpaceAttributes() just changed. So I feel using CPU
>     arch protocol is a bit safer. Anyway, I'll change it.
> (7) I did put those macros in the install function before. To reduce the
>      number of changed files, I made current changes. You're right it's
>      not worthy.
> (8) Using macro can help the readability, which is more important to me.
>     I know function can do the same. But it looks a bit heavy in this situation.
>     I have to admit replacing  the macros with a library is a very good idea,
>     which brings the same readability. I didn't think of that before. Although
>     Library is still a little bit heavy to me but it's in a different way, I think it
>     worth a trying.
> (9) Putting a space before open parenthesis is forced style? If so, I'll add it.
> (10) You're right. Using library can reduce the disturbs to affected drivers
>        by this feature to the minimum.
>
> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Thursday, September 14, 2017 7:35 AM
> To: Wang, Jian J <jian.j.wang@intel.com<mailto:jian.j.wang@intel.com>>
> Cc: edk2-devel@lists.01.org<mailto:edk2-devel@lists.01.org>; Justen, Jordan L <jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>; Dong, Eric <eric.dong@intel.com<mailto:eric.dong@intel.com>>; Kinney, Michael D <michael.d.kinney@intel.com<mailto:michael.d.kinney@intel.com>>; Wolman, Ayellet <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>; Yao, Jiewen <jiewen.yao@intel.com<mailto:jiewen.yao@intel.com>>; Zeng, Star <star.zeng@intel.com<mailto:star.zeng@intel.com>>
> Subject: Re: [edk2] [PATCH 4/4] OvmfPkg/QemuVideoDxe: Update QemuVideoDxe driver to bypass NULL pointer detection if enabled.
>
> Hi,
>
> some of the points I'm going to make have already been pointed out by
> Jordan:
>
> (1) When posting a patch series, please collect the Cc: tags from all of
> the patches, and add them *all* to the cover letter. This way everyone
> will get a personal copy of the general description.
>
>
> (2) The subject line is too long. One possible simplification:
>
> OvmfPkg/QemuVideoDxe: bypass NULL pointer detection
>
>
> On 09/13/17 11:25, Wang, Jian J wrote:
>> QemuVideoDxe driver will install VBE SHIM into page 0. If NULL pointer
>> detection is enabled, page 0 must be enabled temporarily before
>> installing and disabled again afterwards. For Windows 7 boot, BIT7 of
>> PcdNullPointerDetectionPropertyMask must still be set to avoid hang.
>
> (3) Subject line and commit message both should not exceed 74 characters
> line length. (Not sure how many chars PatchCheck.py actually enforces, I
> always stick with 74, following the Linux kernel tradition.)
>
> I rewrapped the commit message here for readability.
>
>
>>
>> Cc: Jiewen Yao <jiewen.yao@intel.com<mailto:jiewen.yao@intel.com>>
>> Cc: Eric Dong <eric.dong@intel.com<mailto:eric.dong@intel.com>>
>> Cc: Star Zeng <star.zeng@intel.com<mailto:star.zeng@intel.com>>
>> Cc: Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>
>> Cc: Justen, Jordan L <jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>
>> Cc: Kinney, Michael D <michael.d.kinney@intel.com<mailto:michael.d.kinney@intel.com>>
>> Cc: Wolman, Ayellet <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>
>> Suggested-by: Wolman, Ayellet <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Wang, Jian J <jian.j.wang@intel.com<mailto:jian.j.wang@intel.com>>
>
> (4) I think this is also something that Jordan had pointed out a long
> time ago (apologies if I mis-remember):
>
> The strings after the tags should form correct email addresses, and if
> there are various email meta-characters in them, like "." (dot) and ","
> (comma), then they should be quoted, like this:
>
> Cc: "Justen, Jordan L" <jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>
> Cc: "Kinney, Michael D" <michael.d.kinney@intel.com<mailto:michael.d.kinney@intel.com>>
> Cc: "Wolman, Ayellet" <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>
> Suggested-by: "Wolman, Ayellet" <ayellet.wolman@intel.com<mailto:ayellet.wolman@intel.com>>
> Signed-off-by: "Wang, Jian J" <jian.j.wang@intel.com<mailto:jian.j.wang@intel.com>>
>
> If you look at the actual addresses on the emails that have been sent
> out, you can see they are all malformed. For example, I have:
>
> "Jordan L <jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>" for Jordan -- the part before the
> comma was taken to be a separate email address (a malformed one).
>
> At least for my reply, I have fixed up the email addresses.
>
>
> (5) The commit message mentions BIT7 of the new PCD.
>
> First, thanks for checking Windows 7 boot (and I'm happy that I got
> suspicious of the feature with regard to Windows 7). I think BIT7 is a
> good feature.
>
> However, please include the short description of that feature in the
> commit message -- it is one sentence; "Disable NULL pointer detection
> just after EndOfDxe."
>
> (I think BIT7 is a really smart feature, and I like *how* it is used in
> "NULL_DETECTION_ENABLED" below. The check means, "if the protection is
> enabled for DXE, and *not disabled* (== also enabled) after End-of-Dxe".
>
> This doesn't mean that I like the NULL_DETECTION_ENABLED macro itself;
> more on that below.)
>
>
>> ---
>>  OvmfPkg/QemuVideoDxe/Driver.c         | 15 ++++++++++++++-
>>  OvmfPkg/QemuVideoDxe/Qemu.h           | 16 ++++++++++++++++
>>  OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf |  2 ++
>>  3 files changed, 32 insertions(+), 1 deletion(-)
>>
>> diff --git a/OvmfPkg/QemuVideoDxe/Driver.c b/OvmfPkg/QemuVideoDxe/Driver.c
>> index 0dce80e59b..ee0eed7214 100644
>> --- a/OvmfPkg/QemuVideoDxe/Driver.c
>> +++ b/OvmfPkg/QemuVideoDxe/Driver.c
>> @@ -194,6 +194,7 @@ QemuVideoControllerDriverStart (
>>    PCI_TYPE00                        Pci;
>>    QEMU_VIDEO_CARD                   *Card;
>>    EFI_PCI_IO_PROTOCOL               *ChildPciIo;
>> +  EFI_CPU_ARCH_PROTOCOL             *Cpu;
>
> (6) I believe I mentioned this in the earlier discussion, in some form,
> but now I'll say it again:
>
> A UEFI driver has no business poking at the CPU Arch protocol. The PI
> spec (1.6) states,
>
>   12.3 CPU Architectural Protocol
>   EFI_CPU_ARCH_PROTOCOL
>
>   Summary
>
>   Abstracts the processor services that are required to implement some
>   of the DXE services. This protocol must be produced by a boot service
>   or runtime DXE driver and may only be consumed by the DXE Foundation
>   and DXE drivers that produce architectural protocols.
>
> The DXE core is obviously free to use the CPU Arch protocol, but a UEFI
> driver is forbidden from it, *even if* we say that, in this UEFI driver,
> we are going to use DXE services. (Which come from the PI spec, and not
> the UEFI spec.)
>
> Therefore, here we have to use gDS->SetMemorySpaceAttributes().
>
> The gDS->SetMemorySpaceAttributes() service depends on the CPU Arch
> protocol, by the PI spec. It is not easy to see, because the PI spec has
> a formatting error in this area. If you look under
> GetMemorySpaceDescriptor(), there is an error code
>
>   EFI_NOT_AVAILABLE_YET  The attributes cannot be set because CPU
>                          architectural protocol is not available yet.
>
> Obviously this error code belongs to SetMemorySpaceAttributes(), not
> GetMemorySpaceDescriptor().
>
> Anyway, gDS should be used, architectural protocols shouldn't be.
>
>
>>
>>    OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
>>
>> @@ -479,7 +480,19 @@ QemuVideoControllerDriverStart (
>>  #if defined MDE_CPU_IA32 || defined MDE_CPU_X64
>>    if (Private->Variant == QEMU_VIDEO_BOCHS_MMIO ||
>>        Private->Variant == QEMU_VIDEO_BOCHS) {
>> -    InstallVbeShim (Card->Name, Private->GraphicsOutput.Mode->FrameBufferBase);
>> +    //
>> +    // Prepare CPU arch protocol for NULL pointer detection
>> +    //
>> +    Status = gBS->LocateProtocol (
>> +                    &gEfiCpuArchProtocolGuid,
>> +                    NULL,
>> +                    (VOID **) &Cpu
>> +                    );
>> +    ASSERT_EFI_ERROR (Status);
>> +
>> +    DISABLE_NULL_DETECTION(Cpu);
>> +      InstallVbeShim (Card->Name, Private->GraphicsOutput.Mode->FrameBufferBase);
>> +    ENABLE_NULL_DETECTION(Cpu);
>
> (7) The NULL detection disabling and enabling should bracket the
> affected code as tightly as possible.
>
> So please move this into InstallVbeShim() accordingly.
>
>
>>    }
>>  #endif
>>
>> diff --git a/OvmfPkg/QemuVideoDxe/Qemu.h b/OvmfPkg/QemuVideoDxe/Qemu.h
>> index 7fbb25b3ef..bb3bc6eb0f 100644
>> --- a/OvmfPkg/QemuVideoDxe/Qemu.h
>> +++ b/OvmfPkg/QemuVideoDxe/Qemu.h
>> @@ -25,6 +25,7 @@
>>  #include <Protocol/PciIo.h>
>>  #include <Protocol/DriverSupportedEfiVersion.h>
>>  #include <Protocol/DevicePath.h>
>> +#include <Protocol/Cpu.h>
>>
>>  #include <Library/DebugLib.h>
>>  #include <Library/UefiDriverEntryPoint.h>
>> @@ -82,6 +83,21 @@ typedef struct {
>>
>>  #define GRAPHICS_OUTPUT_INVALIDE_MODE_NUMBER  0xffff
>>
>> +//
>> +// VBE code will access memory between 0-4095 which will cause page fault exception
>> +// if NULL pointer detection mechanism is enabled. Following macros can be used to
>> +// disable/enable NULL pointer detection before/after accessing those memory.
>> +//
>> +#define NULL_DETECTION_ENABLED  ((PcdGet8(PcdNullPointerDetectionPropertyMask) & (BIT0|BIT7)) == BIT0)
>> +#define DISABLE_NULL_DETECTION(Cpu)                                             \
>> +  if (NULL_DETECTION_ENABLED) {                                                 \
>> +    (Cpu)->SetMemoryAttributes((Cpu), 0, EFI_PAGE_SIZE, 0);                     \
>> +  }
>> +#define ENABLE_NULL_DETECTION(Cpu)                                              \
>> +  if (NULL_DETECTION_ENABLED) {                                                 \
>> +    (Cpu)->SetMemoryAttributes((Cpu), 0, EFI_PAGE_SIZE, EFI_MEMORY_RP);         \
>> +  }
>> +
>
> (8) I believe Jordan too commented on these macros elsewhere (under
> patch 1/4).
>
> In my opinion, this functionality should be extracted into a library
> class, with a library instance that is suitable for at least UEFI_DRIVER
> modules. (Maybe even for DXE_DRIVER modules.)
>
> You could add a separate library instance for SMM drivers, if that were
> necessary.
>
>
> (9) Style comment: please put one space character between the function
> designator and the opening parenthesis.
>
>
>>  //
>>  // QEMU Video Private Data Structure
>>  //
>> diff --git a/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf b/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf
>> index 7c7d429bca..5d166eb99c 100644
>> --- a/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf
>> +++ b/OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf
>> @@ -72,7 +72,9 @@
>>    gEfiGraphicsOutputProtocolGuid                # PROTOCOL BY_START
>>    gEfiDevicePathProtocolGuid                    # PROTOCOL BY_START
>>    gEfiPciIoProtocolGuid                         # PROTOCOL TO_START
>> +  gEfiCpuArchProtocolGuid
>>
>>  [Pcd]
>>    gOptionRomPkgTokenSpaceGuid.PcdDriverSupportedEfiVersion
>> +  gEfiMdeModulePkgTokenSpaceGuid.PcdNullPointerDetectionPropertyMask
>
> (10) Instead of these, the library class that I described under (8)
> should be added here.
>
> Any further dependencies like PCDs, protocols etc should be inherited by
> the driver through the library instance that the platform DSC file
> resolves the library class to.
>
> Bonus: should you realize that the feature is impossible to implement
> without accessing the CPU Arch protocol directly, you could hide the
> protocol GUID dependency in the library instance INF file, and I'd be
> none the wiser.
>
> ... Well, I could at least pretend that. :)
>
> Thanks,
> Laszlo
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