linux-kernel - Re: [PATCH 18/30] acpi: Disable APEI error injection if the kernel is locked down

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Date:   Thu, 7 Nov 2019 08:21:40 +0000
From:   Joey Lee <JLee@...e.com>
To:     "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
CC:     David Howells <dhowells@...hat.com>,
        "gnomes@...rguk.ukuu.org.uk" <gnomes@...rguk.ukuu.org.uk>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jforbes@...hat.com" <jforbes@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        James Morris <jmorris@...ei.org>
Subject: Re: [PATCH 18/30] acpi: Disable APEI error injection if the kernel is
 locked down

Hi experts,

On Thu, Nov 09, 2017 at 05:32:53PM +0000, David Howells wrote:
> From: Linn Crosetto <linn@....com>
> 
> ACPI provides an error injection mechanism, EINJ, for debugging and testing
> the ACPI Platform Error Interface (APEI) and other RAS features.  If
> supported by the firmware, ACPI specification 5.0 and later provide for a
> way to specify a physical memory address to which to inject the error.
> 
> Injecting errors through EINJ can produce errors which to the platform are
> indistinguishable from real hardware errors.  This can have undesirable
> side-effects, such as causing the platform to mark hardware as needing
> replacement.
> 
> While it does not provide a method to load unauthenticated privileged code,
> the effect of these errors may persist across reboots and affect trust in
> the underlying hardware, so disable error injection through EINJ if
> the kernel is locked down.
> 
> Signed-off-by: Linn Crosetto <linn@....com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> Reviewed-by: "Lee, Chun-Yi" <jlee@...e.com>
> cc: linux-acpi@...r.kernel.org

I was looking at the lockdown pathes in v5.4-rc kernel and found that the
"acpi: Disable APEI error injection if the kernel is locked down" did not
merged with lockdown patch set. This patch be sent with Matthew's pull
request lockdown patches for 5.2:
    http://kernsec.org/pipermail/linux-security-module-archive/2019-March/012033.html

But it didn't show in Morris's git:
    https://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git/log/?h=next-lockdown

Maybe I missed some detail of this patch. Could anyone point out the
concern of this patch please?

> ---
> 
>  drivers/acpi/apei/einj.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/acpi/apei/einj.c b/drivers/acpi/apei/einj.c
> index b38737c83a24..6d71e1e97b20 100644
> --- a/drivers/acpi/apei/einj.c
> +++ b/drivers/acpi/apei/einj.c
> @@ -518,6 +518,9 @@ static int einj_error_inject(u32 type, u32 flags, u64 param1, u64 param2,
>  	int rc;
>  	u64 base_addr, size;
>  
> +	if (kernel_is_locked_down("ACPI error injection"))
> +		return -EPERM;
> +
>  	/* If user manually set "flags", make sure it is legal */
>  	if (flags && (flags &
>  		~(SETWA_FLAGS_APICID|SETWA_FLAGS_MEM|SETWA_FLAGS_PCIE_SBDF)))
> 
> --
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Thanks
Joey Lee