diff mbox series

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

Message ID 20200626155832.2323789-3-ardb@kernel.org (mailing list archive)
State Mainlined
Commit 325f5585ec36953a3fe2e000451f690440fe1bf5
Headers show
Series arm64/acpi: restrict AML opregion memory access | expand

Commit Message

Ard Biesheuvel June 26, 2020, 3:58 p.m. UTC
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>
---
 arch/arm64/kernel/acpi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Shawn Guo Feb. 6, 2021, 3:11 a.m. UTC | #1
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
Ard Biesheuvel Feb. 6, 2021, 8:10 a.m. UTC | #2
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
Ard Biesheuvel Feb. 6, 2021, 10:17 a.m. UTC | #3
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.
Shawn Guo Feb. 6, 2021, 10:45 a.m. UTC | #4
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
diff mbox series

Patch

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