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Date: Sat, 6 Feb 2021 09:10:19 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Shawn Guo <shawn.guo@...aro.org>
Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Catalin Marinas <catalin.marinas@....com>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>, Sudeep Holla <sudeep.holla@....com>,
Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org
Subject: 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 <shawn.guo@...aro.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@...nel.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
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