Re: [PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions

Re: [PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions

[Shawn Guo]

Hi Ard,

On Fri, Jun 26, 2020 at 05:58:32PM +0200, Ard Biesheuvel wrote:
> Given that the contents of EFI runtime code and data regions are
> provided by the firmware, as well as the DSDT, it is not unimaginable
> that AML code exists today that accesses EFI runtime code regions using
> a SystemMemory OpRegion. There is nothing fundamentally wrong with that,
> but since we take great care to ensure that executable code is never
> mapped writeable and executable at the same time, we should not permit
> AML to create writable mapping.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

I'm booting Lenovo Flex 5G laptop with ACPI, and seeing this change
causes a memory abort[1] when upgrading ACPI tables via initrd[2].
Dropping this change seems to fix the issue for me.  But does that
looks like a correct fix to you?

Shawn

[1] https://fileserver.linaro.org/s/iDe9SaZeNNkyNxG
[2] Documentation/admin-guide/acpi/initrd_table_override.rst

> ---
>  arch/arm64/kernel/acpi.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index 01b861e225b0..455966401102 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -301,6 +301,15 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
>  			pr_warn(FW_BUG "requested region covers kernel memory @ %pa\n", &phys);
>  			return NULL;
>  
> +		case EFI_RUNTIME_SERVICES_CODE:
> +			/*
> +			 * This would be unusual, but not problematic per se,
> +			 * as long as we take care not to create a writable
> +			 * mapping for executable code.
> +			 */
> +			prot = PAGE_KERNEL_RO;
> +			break;
> +
>  		case EFI_ACPI_RECLAIM_MEMORY:
>  			/*
>  			 * ACPI reclaim memory is used to pass firmware tables
> -- 
> 2.27.0

Re: [PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions

[Ard Biesheuvel]

On Sat, 6 Feb 2021 at 04:11, Shawn Guo <shawn.guo@linaro.org> wrote:
>
> Hi Ard,
>
> On Fri, Jun 26, 2020 at 05:58:32PM +0200, Ard Biesheuvel wrote:
> > Given that the contents of EFI runtime code and data regions are
> > provided by the firmware, as well as the DSDT, it is not unimaginable
> > that AML code exists today that accesses EFI runtime code regions using
> > a SystemMemory OpRegion. There is nothing fundamentally wrong with that,
> > but since we take great care to ensure that executable code is never
> > mapped writeable and executable at the same time, we should not permit
> > AML to create writable mapping.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>
> I'm booting Lenovo Flex 5G laptop with ACPI, and seeing this change
> causes a memory abort[1] when upgrading ACPI tables via initrd[2].
> Dropping this change seems to fix the issue for me.  But does that
> looks like a correct fix to you?
>
> Shawn
>
> [1] https://fileserver.linaro.org/s/iDe9SaZeNNkyNxG
> [2] Documentation/admin-guide/acpi/initrd_table_override.rst
>

Can you check whether reverting

32cf1a12cad43358e47dac8014379c2f33dfbed4

fixes the issue too?

If it does, please report this as a regression. The OS should not
modify firmware provided tables in-place, regardless of how they were
delivered.

BTW I recently started using my Yoga C630 with Debian, and I am quite
happy with it! Thanks a lot for spending the time on the installer
etc.

I have observed some issues while using mine - I'm happy to share
them, on a mailing list or anywhere else.



> > ---
> >  arch/arm64/kernel/acpi.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> > index 01b861e225b0..455966401102 100644
> > --- a/arch/arm64/kernel/acpi.c
> > +++ b/arch/arm64/kernel/acpi.c
> > @@ -301,6 +301,15 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
> >                       pr_warn(FW_BUG "requested region covers kernel memory @ %pa\n", &phys);
> >                       return NULL;
> >
> > +             case EFI_RUNTIME_SERVICES_CODE:
> > +                     /*
> > +                      * This would be unusual, but not problematic per se,
> > +                      * as long as we take care not to create a writable
> > +                      * mapping for executable code.
> > +                      */
> > +                     prot = PAGE_KERNEL_RO;
> > +                     break;
> > +
> >               case EFI_ACPI_RECLAIM_MEMORY:
> >                       /*
> >                        * ACPI reclaim memory is used to pass firmware tables
> > --
> > 2.27.0

Re: [PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions

[Ard Biesheuvel]

On Sat, 6 Feb 2021 at 09:10, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Sat, 6 Feb 2021 at 04:11, Shawn Guo <shawn.guo@linaro.org> wrote:
> >
> > Hi Ard,
> >
> > On Fri, Jun 26, 2020 at 05:58:32PM +0200, Ard Biesheuvel wrote:
> > > Given that the contents of EFI runtime code and data regions are
> > > provided by the firmware, as well as the DSDT, it is not unimaginable
> > > that AML code exists today that accesses EFI runtime code regions using
> > > a SystemMemory OpRegion. There is nothing fundamentally wrong with that,
> > > but since we take great care to ensure that executable code is never
> > > mapped writeable and executable at the same time, we should not permit
> > > AML to create writable mapping.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >
> > I'm booting Lenovo Flex 5G laptop with ACPI, and seeing this change
> > causes a memory abort[1] when upgrading ACPI tables via initrd[2].
> > Dropping this change seems to fix the issue for me.  But does that
> > looks like a correct fix to you?
> >
> > Shawn
> >
> > [1] https://fileserver.linaro.org/s/iDe9SaZeNNkyNxG
> > [2] Documentation/admin-guide/acpi/initrd_table_override.rst
> >
>
> Can you check whether reverting
>
> 32cf1a12cad43358e47dac8014379c2f33dfbed4
>
> fixes the issue too?
>
> If it does, please report this as a regression. The OS should not
> modify firmware provided tables in-place, regardless of how they were
> delivered.
>

That patch modifies firmware provided tables in-place, which
invalidates checksums and TPM measurements, so it needs to be reverted
in any case, and I have already sent out  the patch for doing so.

Re: [PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions

[Shawn Guo]

On Sat, Feb 06, 2021 at 09:10:19AM +0100, Ard Biesheuvel wrote:
> On Sat, 6 Feb 2021 at 04:11, Shawn Guo <shawn.guo@linaro.org> wrote:
> >
> > Hi Ard,
> >
> > On Fri, Jun 26, 2020 at 05:58:32PM +0200, Ard Biesheuvel wrote:
> > > Given that the contents of EFI runtime code and data regions are
> > > provided by the firmware, as well as the DSDT, it is not unimaginable
> > > that AML code exists today that accesses EFI runtime code regions using
> > > a SystemMemory OpRegion. There is nothing fundamentally wrong with that,
> > > but since we take great care to ensure that executable code is never
> > > mapped writeable and executable at the same time, we should not permit
> > > AML to create writable mapping.
> > >
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >
> > I'm booting Lenovo Flex 5G laptop with ACPI, and seeing this change
> > causes a memory abort[1] when upgrading ACPI tables via initrd[2].
> > Dropping this change seems to fix the issue for me.  But does that
> > looks like a correct fix to you?
> >
> > Shawn
> >
> > [1] https://fileserver.linaro.org/s/iDe9SaZeNNkyNxG
> > [2] Documentation/admin-guide/acpi/initrd_table_override.rst
> >
> 
> Can you check whether reverting
> 
> 32cf1a12cad43358e47dac8014379c2f33dfbed4
> 
> fixes the issue too?

Yes, it does.

> If it does, please report this as a regression. The OS should not
> modify firmware provided tables in-place, regardless of how they were
> delivered.
> 
> BTW I recently started using my Yoga C630 with Debian, and I am quite
> happy with it! Thanks a lot for spending the time on the installer
> etc.

Cool, glad to hear that!

Shawn