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

On Sat, 6 Feb 2021 at 04:11, Shawn Guo [off-list ref] wrote:

Hi Ard,

On Fri, Jun 26, 2020 at 05:58:32PM +0200, Ard Biesheuvel wrote:

quoted

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.

quoted

---
 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

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