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

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

[Arvind Sankar]

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@alum.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

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

[Borislav Petkov]

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@alum.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.

https://people.kernel.org/tglx/notes-about-netiquette

[tip: x86/boot] x86/sysfb: Fix check for bad VRAM size

[tip-bot2 for Arvind Sankar]

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     dacc9092336be20b01642afe1a51720b31f60369
Gitweb:        https://git.kernel.org/tip/dacc9092336be20b01642afe1a51720b31f60369
Author:        Arvind Sankar <nivedita@alum.mit.edu>
AuthorDate:    Tue, 07 Jan 2020 18:04:10 -05:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 20 Jan 2020 10:57:53 +01:00

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
---
 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 01f0e22..298fc1e 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));