efi/libstub: skip GOP with PIXEL_BLT_ONLY format

Message ID 1489650662-3598-1-git-send-email-ard.biesheuvel@linaro.org
State New
Headers show

Commit Message

Ard Biesheuvel March 16, 2017, 7:51 a.m.
From: "Cohen, Eugene" <eugene@hp.com>


The UEFI Specification permits Graphics Output Protocol (GOP) instances
without direct framebuffer access. This is indicated in the Mode structure
with a PixelFormat enumeration value of PIXEL_BLT_ONLY. Given that the
kernel does not know how to drive a Blt() only framebuffer (which is only
permitted before ExitBootServices() anyway), we should disregard such
framebuffers when looking for a GOP instance that is suitable for use as
the boot console.

So modify the EFI GOP initialization to not use a PIXEL_BLT_ONLY instance,
preventing attempts later in boot to use an invalid screen_info.lfb_base
address.

Signed-off-by: Eugene Cohen <eugene@hp.com>

[ardb: clarify that Blt() only GOPs are unusable by the kernel]
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

---
 drivers/firmware/efi/libstub/gop.c | 8 ++++++++
 1 file changed, 8 insertions(+)

-- 
2.7.4

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Comments

Ard Biesheuvel April 4, 2017, 1:18 p.m. | #1
On 16 March 2017 at 07:51, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> From: "Cohen, Eugene" <eugene@hp.com>

>

> The UEFI Specification permits Graphics Output Protocol (GOP) instances

> without direct framebuffer access. This is indicated in the Mode structure

> with a PixelFormat enumeration value of PIXEL_BLT_ONLY. Given that the

> kernel does not know how to drive a Blt() only framebuffer (which is only

> permitted before ExitBootServices() anyway), we should disregard such

> framebuffers when looking for a GOP instance that is suitable for use as

> the boot console.

>

> So modify the EFI GOP initialization to not use a PIXEL_BLT_ONLY instance,

> preventing attempts later in boot to use an invalid screen_info.lfb_base

> address.

>

> Signed-off-by: Eugene Cohen <eugene@hp.com>

> [ardb: clarify that Blt() only GOPs are unusable by the kernel]

> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

> ---

>  drivers/firmware/efi/libstub/gop.c | 8 ++++++++

>  1 file changed, 8 insertions(+)

>

> diff --git a/drivers/firmware/efi/libstub/gop.c b/drivers/firmware/efi/libstub/gop.c

> index 932742e4cf23..b05b282b470d 100644

> --- a/drivers/firmware/efi/libstub/gop.c

> +++ b/drivers/firmware/efi/libstub/gop.c

> @@ -178,6 +178,10 @@ setup_gop32(efi_system_table_t *sys_table_arg, struct screen_info *si,

>         if (!first_gop)

>                 goto out;

>

> +       /* Does the GOP implement a BLT-only framebuffer? */

> +       if (pixel_format == PIXEL_BLT_ONLY)

> +               goto out;

> +

>         /* EFI framebuffer */

>         si->orig_video_isVGA = VIDEO_TYPE_EFI;

>

> @@ -295,6 +299,10 @@ setup_gop64(efi_system_table_t *sys_table_arg, struct screen_info *si,

>         if (!first_gop)

>                 goto out;

>

> +       /* Does the GOP implement a BLT-only framebuffer? */

> +       if (pixel_format == PIXEL_BLT_ONLY)

> +               goto out;

> +

>         /* EFI framebuffer */

>         si->orig_video_isVGA = VIDEO_TYPE_EFI;

>


As it turns out, the patch in its current form triggers a GCC
diagnostic regarding potential uninitialized use of the variables
pixel_format, fb_base, height, width, etc. While the diagnostic
appears to be inaccurate, introducing compiler warnings is frowned
upon and as it turns out, it may actually be more appropriate to move
the BLT-only check into the loop that iterates over the GOP handles,
since that way, there may still be other GOP candidates if we
disregard the ones that are BLT-only.

So the version that is going upstream will be updated in this regard.
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Patch hide | download patch | download mbox

diff --git a/drivers/firmware/efi/libstub/gop.c b/drivers/firmware/efi/libstub/gop.c
index 932742e4cf23..b05b282b470d 100644
--- a/drivers/firmware/efi/libstub/gop.c
+++ b/drivers/firmware/efi/libstub/gop.c
@@ -178,6 +178,10 @@  setup_gop32(efi_system_table_t *sys_table_arg, struct screen_info *si,
 	if (!first_gop)
 		goto out;
 
+	/* Does the GOP implement a BLT-only framebuffer? */
+	if (pixel_format == PIXEL_BLT_ONLY)
+		goto out;
+
 	/* EFI framebuffer */
 	si->orig_video_isVGA = VIDEO_TYPE_EFI;
 
@@ -295,6 +299,10 @@  setup_gop64(efi_system_table_t *sys_table_arg, struct screen_info *si,
 	if (!first_gop)
 		goto out;
 
+	/* Does the GOP implement a BLT-only framebuffer? */
+	if (pixel_format == PIXEL_BLT_ONLY)
+		goto out;
+
 	/* EFI framebuffer */
 	si->orig_video_isVGA = VIDEO_TYPE_EFI;