Re: [PATCH] x86/efi-bgrt: remove the check of the version field

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Ingo Molnar]

* Icenowy Zheng <icenowy@aosc.xyz> wrote:

> Some broken firmwares have a wrongly filled version field in BGRT table.
> (See http://wiki.osdev.org/Broken_UEFI_implementations )
> 
> As we know, these firmwares can also provide correct BGRT image, although
> the table is wrong.
> 
> After removing the check of the version field, the kernel can now extract
> the image correctly, and the information is also correct.
> 
> Tested on a Thinkpad E531 (68854UC).

What's the practical effects of the bug - what problems does a missing 
/sys/firmware/acpi/bgrt/ cause?

I.e. how does the user notice?

Thanks,

	Ingo

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Ingo Molnar]

* Icenowy Zheng <icenowy@aosc.xyz> wrote:

> 
> 
> 10.08.2016, 20:52, "Ingo Molnar" <mingo@kernel.org>:
> > * Icenowy Zheng <icenowy@aosc.xyz> wrote:
> >
> >>  Some broken firmwares have a wrongly filled version field in BGRT table.
> >>  (See http://wiki.osdev.org/Broken_UEFI_implementations )
> >>
> >>  As we know, these firmwares can also provide correct BGRT image, although
> >>  the table is wrong.
> >>
> >>  After removing the check of the version field, the kernel can now extract
> >>  the image correctly, and the information is also correct.
> >>
> >>  Tested on a Thinkpad E531 (68854UC).
> >
> > What's the practical effects of the bug - what problems does a missing
> > /sys/firmware/acpi/bgrt/ cause?
> 
> Currently nothing uses this featues. However, one of my friend is trying to
> develop a splash screen which uses ACPI BGRT, like the splash screen
> of Windows 8 and above.
> Without the directory, there won't be any way to retrieve the vendor splash
> logo.

Ok - please add this information to the changelog.

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Matt Fleming]

On Tue, 09 Aug, at 01:25:46PM, Icenowy Zheng wrote:
> Some broken firmwares have a wrongly filled version field in BGRT table.
> (See http://wiki.osdev.org/Broken_UEFI_implementations )
> 
> As we know, these firmwares can also provide correct BGRT image, although
> the table is wrong.
> 
> After removing the check of the version field, the kernel can now extract
> the image correctly, and the information is also correct.
> 
> Tested on a Thinkpad E531 (68854UC).
> 
> Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
> ---
>  arch/x86/platform/efi/efi-bgrt.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/efi-bgrt.c
> index 6a2f569..f492ea0 100644
> --- a/arch/x86/platform/efi/efi-bgrt.c
> +++ b/arch/x86/platform/efi/efi-bgrt.c
> @@ -47,11 +47,6 @@ void __init efi_bgrt_init(void)
>  		       bgrt_tab->header.length, sizeof(*bgrt_tab));
>  		return;
>  	}
> -	if (bgrt_tab->version != 1) {
> -		pr_notice("Ignoring BGRT: invalid version %u (expected 1)\n",
> -		       bgrt_tab->version);
> -		return;
> -	}
>  	if (bgrt_tab->status & 0xfe) {
>  		pr_notice("Ignoring BGRT: reserved status bits are non-zero %u\n",
>  		       bgrt_tab->status);

This would be less scary if we checked for known broken and known good
version values instead of removing the check altogether, i.e. 0 and 1.

The whole point of the version field is that it tells us about the
layout of the BGRT table, so it's not exactly a useless check.

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Josh Triplett]

On Mon, Aug 15, 2016 at 01:56:43PM +0100, Matt Fleming wrote:
> On Tue, 09 Aug, at 01:25:46PM, Icenowy Zheng wrote:
> > Some broken firmwares have a wrongly filled version field in BGRT table.
> > (See http://wiki.osdev.org/Broken_UEFI_implementations )
> > 
> > As we know, these firmwares can also provide correct BGRT image, although
> > the table is wrong.
> > 
> > After removing the check of the version field, the kernel can now extract
> > the image correctly, and the information is also correct.
> > 
> > Tested on a Thinkpad E531 (68854UC).
> > 
> > Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
> > ---
> >  arch/x86/platform/efi/efi-bgrt.c | 5 -----
> >  1 file changed, 5 deletions(-)
> > 
> > diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/efi-bgrt.c
> > index 6a2f569..f492ea0 100644
> > --- a/arch/x86/platform/efi/efi-bgrt.c
> > +++ b/arch/x86/platform/efi/efi-bgrt.c
> > @@ -47,11 +47,6 @@ void __init efi_bgrt_init(void)
> >  		       bgrt_tab->header.length, sizeof(*bgrt_tab));
> >  		return;
> >  	}
> > -	if (bgrt_tab->version != 1) {
> > -		pr_notice("Ignoring BGRT: invalid version %u (expected 1)\n",
> > -		       bgrt_tab->version);
> > -		return;
> > -	}
> >  	if (bgrt_tab->status & 0xfe) {
> >  		pr_notice("Ignoring BGRT: reserved status bits are non-zero %u\n",
> >  		       bgrt_tab->status);
> 
> This would be less scary if we checked for known broken and known good
> version values instead of removing the check altogether, i.e. 0 and 1.
> 
> The whole point of the version field is that it tells us about the
> layout of the BGRT table, so it's not exactly a useless check.

Agreed.  It seems likely that BIOSes would have incorrectly left the
version at 0.  It seems less likely that they'd set it to some other
random value.

So, I'd suggest changing the check to pr_debug and continue for 0,
continue for 1, and pr_notice and abort for anything else.

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Dave Young]

On 08/15/16 at 01:56pm, Matt Fleming wrote:
> On Tue, 09 Aug, at 01:25:46PM, Icenowy Zheng wrote:
> > Some broken firmwares have a wrongly filled version field in BGRT table.
> > (See http://wiki.osdev.org/Broken_UEFI_implementations )
> > 
> > As we know, these firmwares can also provide correct BGRT image, although
> > the table is wrong.
> > 
> > After removing the check of the version field, the kernel can now extract
> > the image correctly, and the information is also correct.
> > 
> > Tested on a Thinkpad E531 (68854UC).
> > 
> > Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
> > ---
> >  arch/x86/platform/efi/efi-bgrt.c | 5 -----
> >  1 file changed, 5 deletions(-)
> > 
> > diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/efi-bgrt.c
> > index 6a2f569..f492ea0 100644
> > --- a/arch/x86/platform/efi/efi-bgrt.c
> > +++ b/arch/x86/platform/efi/efi-bgrt.c
> > @@ -47,11 +47,6 @@ void __init efi_bgrt_init(void)
> >  		       bgrt_tab->header.length, sizeof(*bgrt_tab));
> >  		return;
> >  	}
> > -	if (bgrt_tab->version != 1) {
> > -		pr_notice("Ignoring BGRT: invalid version %u (expected 1)\n",
> > -		       bgrt_tab->version);
> > -		return;
> > -	}
> >  	if (bgrt_tab->status & 0xfe) {
> >  		pr_notice("Ignoring BGRT: reserved status bits are non-zero %u\n",
> >  		       bgrt_tab->status);
> 
> This would be less scary if we checked for known broken and known good
> version values instead of removing the check altogether, i.e. 0 and 1.

Could we add some quirk for these broken hardware instead of changing
the normal code?

> 
> The whole point of the version field is that it tells us about the
> layout of the BGRT table, so it's not exactly a useless check.

Agreed.

Thanks
Dave

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Matt Fleming]

On Wed, 17 Aug, at 01:44:13PM, Dave Young wrote:
> 
> Could we add some quirk for these broken hardware instead of changing
> the normal code?

I'd prefer not to do that if possible. Due to the way that the BIOS
ecosystem works, this kind of broken firmware spreads across the
industry, appearing in newer versions of products from the same vendor
and even products from different vendors.

Continuously updating a quirks table as additional broken platforms
are discovered simply does not scale.

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Dave Young]

On 08/18/16 at 09:41pm, Matt Fleming wrote:
> On Wed, 17 Aug, at 01:44:13PM, Dave Young wrote:
> > 
> > Could we add some quirk for these broken hardware instead of changing
> > the normal code?
> 
> I'd prefer not to do that if possible. Due to the way that the BIOS
> ecosystem works, this kind of broken firmware spreads across the
> industry, appearing in newer versions of products from the same vendor
> and even products from different vendors.
> 
> Continuously updating a quirks table as additional broken platforms
> are discovered simply does not scale.

Ok, I assumed that they are limited like one point in the web url
http://wiki.osdev.org/Broken_UEFI_implementations 

But I arm probably wrong like you said. Please ignore the comment then.

Thanks
Dave

Re: [PATCH] x86/efi-bgrt: remove the check of the version field

[Dave Young]

On 08/22/16 at 04:49pm, Icenowy Zheng wrote:
> 
> 
> 22.08.2016, 15:28, "Dave Young" <dyoung@redhat.com>:
> > On 08/18/16 at 09:41pm, Matt Fleming wrote:
> >>  On Wed, 17 Aug, at 01:44:13PM, Dave Young wrote:
> >>  >
> >>  > Could we add some quirk for these broken hardware instead of changing
> >>  > the normal code?
> >>
> >>  I'd prefer not to do that if possible. Due to the way that the BIOS
> >>  ecosystem works, this kind of broken firmware spreads across the
> >>  industry, appearing in newer versions of products from the same vendor
> >>  and even products from different vendors.
> >>
> >>  Continuously updating a quirks table as additional broken platforms
> >>  are discovered simply does not scale.
> >
> > Ok, I assumed that they are limited like one point in the web url
> > http://wiki.osdev.org/Broken_UEFI_implementations
> 
> At least I think all Thinkpads suffer from this.

Icenowy, sorry for late reply, I missed it. I'm not sure other version, but my
T440s does work well.

> 
> >
> > But I arm probably wrong like you said. Please ignore the comment then.
> >

Thanks
Dave