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

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Date:   Wed, 15 Jan 2020 14:12:06 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Christopher Head <bugs@...ad.ca>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/sysfb: Fix check for bad VRAM size

On Tue, Jan 07, 2020 at 06:04:10PM -0500, Arvind Sankar wrote:
> 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));
> -- 

Christopher,

can I add your Reported-by: and Tested-by: tags to the patch?

Thx.

-- 
Regards/Gruss,
    Boris.

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