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

From: Ard Biesheuvel <ardb@kernel.org>
To: Shawn Guo <shawn.guo@linaro.org>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	 Kernel Hardening <kernel-hardening@lists.openwall.com>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	 ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	 Will Deacon <will@kernel.org>,
	linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions
Date: Sat, 6 Feb 2021 09:10:19 +0100	[thread overview]
Message-ID: <CAMj1kXHSkBcSDuHbsFMJjC89JrO8TxYUoabDmWerNp27s45Ngw@mail.gmail.com> (raw)
In-Reply-To: <20210206031145.GA27503@dragon>

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