linux-kernel - [PATCH] x86/sysfb: Fix check for bad VRAM size

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Message-Id: <20200107230410.2291947-1-nivedita@alum.mit.edu>
Date:   Tue,  7 Jan 2020 18:04:10 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Christopher Head <bugs@...ad.ca>
Subject: [PATCH] x86/sysfb: Fix check for bad VRAM size

When checking whether the reported lfb_size makes sense, we PAGE_ALIGN
height * stride 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 kernel bugzilla linked, an 800x600x32 EFI
framebuffer gets skipped because of this.

Move the PAGE_ALIGN to after the check vs size.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206051
Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 arch/x86/kernel/sysfb_simplefb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sysfb_simplefb.c b/arch/x86/kernel/sysfb_simplefb.c
index 01f0e2263b86..298fc1edd9c9 100644
--- 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));
-- 
2.24.1