x86/sysfb: Fix check for bad VRAM size

When checking whether the reported lfb_size makes sense, the height
* stride result is page-aligned before seeing whether it exceeds the
reported size.

This doesn't work if height * stride is not an exact number of pages.
For example, as reported in the kernel bugzilla below, an 800x600x32 EFI
framebuffer gets skipped because of this.

Move the PAGE_ALIGN to after the check vs size.

Reported-by: Christopher Head <chead@chead.ca>
Tested-by: Christopher Head <chead@chead.ca>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206051
Link: https://lkml.kernel.org/r/20200107230410.2291947-1-nivedita@alum.mit.edu

diff --git a/arch/x86/kernel/sysfb_simplefb.c b/arch/x86/kernel/sysfb_simplefb.c
index 01f0e22..298fc1e 100644 (file)
--- a/arch/x86/kernel/sysfb_simplefb.c
+++ b/arch/x86/kernel/sysfb_simplefb.c
@@ -90,11 +90,11 @@ __init int create_simplefb(const struct screen_info *si,
        if (si->orig_video_isVGA == VIDEO_TYPE_VLFB)
                size <<= 16;
        length = mode->height * mode->stride;
-       length = PAGE_ALIGN(length);
        if (length > size) {
                printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n");
                return -EINVAL;
        }
+       length = PAGE_ALIGN(length);
 
        /* setup IORESOURCE_MEM as framebuffer memory */
        memset(&res, 0, sizeof(res));