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

[joeyli]

Hi all,

On Thu, Nov 07, 2019 at 04:21:31PM +0800, joeyli wrote:
> Hi experts,
> 
> On Thu, Nov 09, 2017 at 05:32:53PM +0000, David Howells wrote:
> > From: Linn Crosetto <linn at hpe.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 at hpe.com>
> > Signed-off-by: David Howells <dhowells at redhat.com>
> > Reviewed-by: "Lee, Chun-Yi" <jlee at suse.com>
> > cc: linux-acpi at vger.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?
>

After a couple of years, we still didn't have this patch in mainline. 
Does that mean the "APEI error injection" doesn't need to be locked down?

Actually this patch is against a CVE-2016-3695:
https://nvd.nist.gov/vuln/detail/CVE-2016-3695

It's before lockdown patchset be merged to kernel mainline. So this CVE
happened in downstream destro. Just search CVE-2016-3695 then we can see
many distros has this.

If mainline kernel doesn't have this patch, then I believe that the
CVE-2016-3695 is also in current mainline kernel.

Then why this patch not be acceptted?

Thanks!
Joey Lee
 
> > ---
> > 
> >  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