On 16 March 2017 at 07:51, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > From: "Cohen, Eugene" <eugene@xxxxxx> > > 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@xxxxxx> > [ardb: clarify that Blt() only GOPs are unusable by the kernel] > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > --- > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
