linux-kernel - Re: [PATCH] fbdev: remove unnecessary memset in vfb

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Message-ID: <55D59851.7010205@ti.com>
Date:	Thu, 20 Aug 2015 12:05:21 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Marcin Chojnacki <marcinch7@...il.com>
CC:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fbdev: remove unnecessary memset in vfb


On 20/08/15 11:21, Geert Uytterhoeven wrote:
> On Thu, Jun 18, 2015 at 3:01 PM, Marcin Chojnacki <marcinch7@...il.com> wrote:
>> In vfb_probe memory is allocated using rvmalloc which automatically
>> sets the allocated memory to zero. This patch removes the second
>> unnecessary memset in vfb_probe.
>>
>> Signed-off-by: Marcin Chojnacki <marcinch7@...il.com>
>> ---
>>  drivers/video/fbdev/vfb.c | 8 --------
>>  1 file changed, 8 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/vfb.c b/drivers/video/fbdev/vfb.c
>> index 70a897b..b2d38b7 100644
>> --- a/drivers/video/fbdev/vfb.c
>> +++ b/drivers/video/fbdev/vfb.c
>> @@ -490,14 +490,6 @@ static int vfb_probe(struct platform_device *dev)
>>         if (!(videomemory = rvmalloc(videomemorysize)))
>>                 return retval;
>>
>> -       /*
>> -        * VFB must clear memory to prevent kernel info
>> -        * leakage into userspace
>> -        * VGA-based drivers MUST NOT clear memory if
>> -        * they want to be able to take over vgacon
>> -        */
>> -       memset(videomemory, 0, videomemorysize);
>> -
> 
> As vfb also serves as a sample driver, I think it would be worthwhile to move
> the comment to rvmalloc().

I changed the patch as follows:


commit c0a3229313d6931a77e0c1e1c22e398c0312bf6f
Author: Marcin Chojnacki <marcinch7@...il.com>
Date:   Thu Jun 18 15:01:52 2015 +0200

    fbdev: remove unnecessary memset in vfb
    
    In vfb_probe memory is allocated using rvmalloc which automatically
    sets the allocated memory to zero. This patch removes the second
    unnecessary memset in vfb_probe.
    
    Signed-off-by: Marcin Chojnacki <marcinch7@...il.com>
    Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>

diff --git a/drivers/video/fbdev/vfb.c b/drivers/video/fbdev/vfb.c
index 70a897b1e458..b9c2f81fb6b9 100644
--- a/drivers/video/fbdev/vfb.c
+++ b/drivers/video/fbdev/vfb.c
@@ -51,7 +51,14 @@ static void *rvmalloc(unsigned long size)
 	if (!mem)
 		return NULL;
 
-	memset(mem, 0, size); /* Clear the ram out, no junk to the user */
+	/*
+	 * VFB must clear memory to prevent kernel info
+	 * leakage into userspace
+	 * VGA-based drivers MUST NOT clear memory if
+	 * they want to be able to take over vgacon
+	 */
+
+	memset(mem, 0, size);
 	adr = (unsigned long) mem;
 	while (size > 0) {
 		SetPageReserved(vmalloc_to_page((void *)adr));
@@ -490,14 +497,6 @@ static int vfb_probe(struct platform_device *dev)
 	if (!(videomemory = rvmalloc(videomemorysize)))
 		return retval;
 
-	/*
-	 * VFB must clear memory to prevent kernel info
-	 * leakage into userspace
-	 * VGA-based drivers MUST NOT clear memory if
-	 * they want to be able to take over vgacon
-	 */
-	memset(videomemory, 0, videomemorysize);
-
 	info = framebuffer_alloc(sizeof(u32) * 256, &dev->dev);
 	if (!info)
 		goto err;


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