回复: [edk2-devel] [PATCH 1/1] MdeModulePkg/VariableRuntimeDxe: avoid double VA conversion of FVB protocol
Ard:
> -邮件原件-
> 发件人: devel@edk2.groups.io 代表 Laszlo Ersek
> 发送时间: 2021年3月16日 23:58
> 收件人: Ard Biesheuvel ; devel@edk2.groups.io
> 抄送: liming@intel.com; j...@solid-run.com; l...@nuviainc.com
> 主题: Re: [edk2-devel] [PATCH 1/1] MdeModulePkg/VariableRuntimeDxe:
> avoid double VA conversion of FVB protocol
>
> On 03/13/21 00:05, Ard Biesheuvel wrote:
> > For historical reasons, the VariableRuntimeDxe performs virtual address
> > conversion on the FVB protocol member pointers of the protocol instance
> > that backs the EFI variable store. However, the driver that produces the
> > actual instance should be doing this, as it is the owner, and provides
> > the actual implementation of those methods.
> >
> > Unfortunately, we cannot simply change this: existing drivers may rely
> > on this behavior, and so the variable driver should take care to only
> > convert the pointers when necessary, but leave them alone when the owner
> > is taking care of this.
To answer Laszlo question, I want to know the impact for the simple fix.
> >
> > The virtual address switch event can be delivered in arbitrary order, and
> > so we should take care of this in a way that does not rely on whether this
> > driver converts its pointers either before or after the owner of the FVB
> > protocol receives the event.
> >
> > So let's not convert the pointers at all when the event is delivered, but
> > record the converted addresses in a shadow FVB protocol. This way, we can
> > check when the variable driver is invoked at runtime whether the switch
> > has occurred or not, and perform the switch if it hasn't.
> >
> > Signed-off-by: Ard Biesheuvel
> > ---
> > Build tested only.
> >
> > MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c | 50
> +---
> > 1 file changed, 43 insertions(+), 7 deletions(-)
> >
> > diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > index 0fca0bb2a9b5..3d83ac4452ee 100644
> > --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> > @@ -37,6 +37,8 @@ EDKII_VAR_CHECK_PROTOCOL
> mVarCheck = { VarCheckRegis
> >
> VarCheckVariablePropertySet,
> >
> VarCheckVariablePropertyGet };
> >
> > +STATIC EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL
> mFvbProtocolShadow;
> > +
> > /**
> >Some Secure Boot Policy Variable may update following other variable
> changes(SecureBoot follows PK change, etc).
> >Record their initial State when variable write service is ready.
> > @@ -105,8 +107,26 @@ AcquireLockOnlyAtBootTime (
> >IN EFI_LOCK *Lock
> >)
> > {
>
> (1) Why is AcquireLockOnlyAtBootTime() the best place to add this?
>
> (Considering especially the leading comment, "This is a temperary
> function that will be removed when EfiAcquireLock() in UefiLib can
> handle the call in UEFI Runtimer driver in RT phase".)
>
> Obviously, I don't want to create more work for you! I just feel that,
> if this is not the best place, we shouldn't overload this function with
> a new responsibility.
>
> > + EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL *FvbInstance;
> > +
> >if (!AtRuntime ()) {
> > EfiAcquireLock (Lock);
> > + } else {
> > +//
> > +// Check whether we need to swap in the converted pointer values
> for the
> > +// FVB protocol methods
> > +//
> > +FvbInstance = mVariableModuleGlobal->FvbInstance;
> > +if (FvbInstance != NULL &&
> > +FvbInstance->GetBlockSize !=
> mFvbProtocolShadow.GetBlockSize) {
>
> (2) It occurs to me that the following pattern (in a single-threaded
> environment):
>
> if (a != b) {
> a = b;
> }
>
> is just:
>
> a = b;
>
> (the small CPU cost notwithstanding).
>
> And that puts this patch in a bit different light: it's not that we may
> or may not convert. Instead, we *always* convert, the question is *when*
> we apply the result of the conversion.
>
> Functionally, there is no difference, but to me mentally, there'd be a
> difference, if we said "delay applying the runtime conversion until
> first call".
>
> Anyway... just wanted to highlight this: we could drop the GetBlockSize
> funcptr comparison. But, we don't have to.
>
> Given the reviews from Liming and Hao -- and thank you in the first
> place for writing the patch! --, I won't really ask for a v2. I'd just
> somehow prefer the compat logic to be elsewhere, rather than in
> AcquireLockOnlyAtBootTime(). In the first place, I'm not clear what we
> currently use AcquireLockOnlyAtBootTime() for.
>
> Up to the maintainers to decide whether this justifies v2. If not:
>
> Acked-by: Laszlo Ersek
>
> Thanks
> Laszlo
>
> > + FvbInstance->GetBlockSize =
> mFvbProtocolShadow.GetBlockSize;
> > + FvbInstance->GetPhysicalAddress =
> mFvbProtocolShadow.GetPhysicalAddress;
> > + FvbInstance->GetAttributes =
>
回复: [edk2-devel] [PATCH 1/1] MdeModulePkg/VariableRuntimeDxe: avoid double VA conversion of FVB protocol
Ard:
Thanks for your fix. Reviewed-by: Liming Gao
Can you include BZ into the commit message? BZ can mention the correct
conversion solution. Other modules should follow the same way to convert FVB
protocol VA.
Thanks
Liming
> -邮件原件-
> 发件人: devel@edk2.groups.io 代表 Ard
> Biesheuvel
> 发送时间: 2021年3月13日 7:06
> 收件人: devel@edk2.groups.io
> 抄送: ler...@redhat.com; liming@intel.com; j...@solid-run.com;
> l...@nuviainc.com; Ard Biesheuvel
> 主题: [edk2-devel] [PATCH 1/1] MdeModulePkg/VariableRuntimeDxe: avoid
> double VA conversion of FVB protocol
>
> For historical reasons, the VariableRuntimeDxe performs virtual address
> conversion on the FVB protocol member pointers of the protocol instance
> that backs the EFI variable store. However, the driver that produces the
> actual instance should be doing this, as it is the owner, and provides
> the actual implementation of those methods.
>
> Unfortunately, we cannot simply change this: existing drivers may rely
> on this behavior, and so the variable driver should take care to only
> convert the pointers when necessary, but leave them alone when the owner
> is taking care of this.
>
> The virtual address switch event can be delivered in arbitrary order, and
> so we should take care of this in a way that does not rely on whether this
> driver converts its pointers either before or after the owner of the FVB
> protocol receives the event.
>
> So let's not convert the pointers at all when the event is delivered, but
> record the converted addresses in a shadow FVB protocol. This way, we can
> check when the variable driver is invoked at runtime whether the switch
> has occurred or not, and perform the switch if it hasn't.
>
> Signed-off-by: Ard Biesheuvel
> ---
> Build tested only.
>
> MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c | 50
> +---
> 1 file changed, 43 insertions(+), 7 deletions(-)
>
> diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> index 0fca0bb2a9b5..3d83ac4452ee 100644
> --- a/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> +++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
> @@ -37,6 +37,8 @@ EDKII_VAR_CHECK_PROTOCOL
> mVarCheck = { VarCheckRegis
>
> VarCheckVariablePropertySet,
>
> VarCheckVariablePropertyGet };
>
> +STATIC EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL mFvbProtocolShadow;
> +
> /**
>Some Secure Boot Policy Variable may update following other variable
> changes(SecureBoot follows PK change, etc).
>Record their initial State when variable write service is ready.
> @@ -105,8 +107,26 @@ AcquireLockOnlyAtBootTime (
>IN EFI_LOCK *Lock
>)
> {
> + EFI_FIRMWARE_VOLUME_BLOCK_PROTOCOL *FvbInstance;
> +
>if (!AtRuntime ()) {
> EfiAcquireLock (Lock);
> + } else {
> +//
> +// Check whether we need to swap in the converted pointer values for
> the
> +// FVB protocol methods
> +//
> +FvbInstance = mVariableModuleGlobal->FvbInstance;
> +if (FvbInstance != NULL &&
> +FvbInstance->GetBlockSize != mFvbProtocolShadow.GetBlockSize)
> {
> + FvbInstance->GetBlockSize =
> mFvbProtocolShadow.GetBlockSize;
> + FvbInstance->GetPhysicalAddress =
> mFvbProtocolShadow.GetPhysicalAddress;
> + FvbInstance->GetAttributes =
> mFvbProtocolShadow.GetAttributes;
> + FvbInstance->SetAttributes =
> mFvbProtocolShadow.SetAttributes;
> + FvbInstance->Read = mFvbProtocolShadow.Read;
> + FvbInstance->Write = mFvbProtocolShadow.Write;
> + FvbInstance->EraseBlocks=
> mFvbProtocolShadow.EraseBlocks;
> +}
>}
> }
>
> @@ -247,13 +267,22 @@ VariableClassAddressChangeEvent (
>UINTN Index;
>
>if (mVariableModuleGlobal->FvbInstance != NULL) {
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->GetBlockSize);
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->GetPhysicalAddress);
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->GetAttributes);
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->SetAttributes);
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->Read);
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->Write);
> -EfiConvertPointer (0x0, (VOID **)
> >FvbInstance->EraseBlocks);
> +//
> +// This module did not produce the FVB protocol instance that
provides
> the
> +// variable store, so it should not be the one performing the pointer
> +// conversion on its members. However, some FVB protocol
> implementations
> +// may rely on this behavior, which was present in older versions of
this
> +// driver, so we need to perform the conversion if the protocol
producer
> +// fails to do so. So let's record the converted values now, and swap
> them
> +// in later if they haven't changed values.
> +//
> +EfiConvertPointer (0x0, (VOID **));
>
