[PATCH]mtd: map: fixed bug in 64-bit systems

[Wang Haitao]

Thanks for your advice.

Hardware：
        CPU：XLP832,the 64-bit OS
        NOR Flash:S29GL128S 128M
Software:
        Kernel:2.6.32.41
        Filesystem:JFFS2

When writing files, errors appear:
        Write len 182  but return retlen 180
        Write of 182 bytes at 0x072c815c failed. returned -5, retlen 180
        Write len 186  but return retlen 184
        Write of 186 bytes at 0x072caff4 failed. returned -5, retlen 184
These errors exist only in 64-bit systems,not in 32-bit systems. After
analysis, we found that the left shift operation is wrong in
map_word_load_partial. For instance：
        unsigned char buf[3] ={0x9e,0x3a,0xea};
        map_bankwidth(map) is 4;

        for (i=0; i < 3; i++) {
                int bitpos;
                bitpos = (map_bankwidth(map)-1-i)*8;
                orig.x[0] &= ~(0xff << bitpos);
                orig.x[0] |= buf[i] << bitpos;
        }

The value of orig.x[0] is expected to be 0x9e3aeaff, but in this
situation(64-bit System) we'll get the wrong value of 0xffffffff9e3aeaff
due to the 64-bit sign extension:
buf[i] is defined as "unsigned char" and the left-shift operation will
convert it to the type of "signed int", so when left-shift buf[i] by 24
bits, the final result will get the wrong value: 0xffffffff9e3aeaff.

If the left-shift bits are less than 24, then sign extension will not
occur. Whereas the bankwidth of the nor flash we used is 4, therefore this
BUG emerges.

Signed-off-by:Pang Xunlei <pang.xunlei at zte.com.cn>
Signed-off-by: Zhang Yi <zhang.yi20 at zte.com.cn>
Signed-off-by:Lu Zhongjun <lu.zhongjun at zte.com.cn>
Reviewed-by: Jiang Biao <jiang.biao2 at zte.com.cn>
Tested-by: Ma Chenggong <ma.chenggong at zte.com.cn>

diff --git a/include/linux/mtd/map.h b/include/linux/mtd/map.h
index aa30244..18ee717
--- a/include/linux/mtd/map.h
+++ b/include/linux/mtd/map.h
@@ -342,7 +342,7 @@ static inline map_word map_word_load_partial(struct map_info *map, map_word orig
 			bitpos = (map_bankwidth(map)-1-i)*8;
 #endif
 			orig.x[0] &= ~(0xff << bitpos);
-			orig.x[0] |= buf[i-start] << bitpos;
+			orig.x[0] |= (unsigned long)buf[i-start] << bitpos;
 		}
 	}
 	return orig;
@@ -361,7 +361,7 @@ static inline map_word map_word_ff(struct map_info *map)

 	if (map_bankwidth(map) < MAP_FF_LIMIT) {
 		int bw = 8 * map_bankwidth(map);
-		r.x[0] = (1 << bw) - 1;
+		r.x[0] = (1UL << bw) - 1;
 	} else {
 		for (i=0; i<map_words(map); i++)
 			r.x[i] = ~0UL;

Brian Norris <computersforpeace at gmail.com> 写于 2013-08-21 16:57:58:

> Hi Wang,
>
> Can you please resend this patch with a few fixups?
>
> The description below is good, but please wrap it to ~70 characters. It
> is hard to read.
>
> Also, you need to test your patch with scripts/checkpatch.pl both before
> and after you email it -- all your whitespace is mangled (i.e., you use
> spaces where there should be tabs).
>
> See the kernel documentation:
>
>   Documentation/SubmittingPatches
>   Documentation/email-clients.txt
>
> On Wed, Aug 07, 2013 at 03:34:20PM +0800, Wang Haitao wrote:
> > Hardware：
> >          CPU：XLP832,the 64-bit OS
> >          NOR Flash:S29GL128S 128M
> > Software:
> >          Kernel:2.6.32.41
> >          Filesystem:JFFS2
> >
> > When writing files, errors appear:
> >          Write len 182  but return retlen 180
> >          Write of 182 bytes at 0x072c815c failed. returned -5, retlen 180
> >          Write len 186  but return retlen 184
> >          Write of 186 bytes at 0x072caff4 failed. returned -5, retlen 184
> > These errors exist only in 64-bit systems,not in 32-bit systems.
> After analysis, we found that the left shift operation is wrong in
> map_word_load_partial. For instance：
> >          unsigned char buf[3] ={0x9e,0x3a,0xea};
> >          map_bankwidth(map) is 4;
> >
> >          for (i=0; i < 3; i++) {
> >                    int bitpos;
> >                    bitpos = (map_bankwidth(map)-1-i)*8;
> >                    orig.x[0] &= ~(0xff << bitpos);
> >                    orig.x[0] |= buf[i] << bitpos;
> >          }
> >
> > The value of orig.x[0] is expected to be 0x9e3aeaff, but in this
> situation(64-bit System) we'll get the wrong value of
> 0xffffffff9e3aeaff due to the 64-bit sign extension:
> > buf[i] is defined as "unsigned char" and the left-shift operation
> will convert it to the type of "signed int", so when left-shift
> buf[i] by 24 bits, the final result will get the wrong value:
> 0xffffffff9e3aeaff.
> >
> > If the left-shift bits are less than 24, then sign extension will
> not occur. Whereas the bankwidth of the nor flash we used is 4,
> therefore this BUG emerges.
> >
> > Signed-off-by:Pang Xunlei <pang.xunlei at zte.com.cn>
> > Signed-off-by: Zhang Yi <zhang.yi20 at zte.com.cn>
> > Signed-off-by:Lu Zhongjun <lu.zhongjun at zte.com.cn>
> > Reviewed-by: Jiang Biao <jiang.biao2 at zte.com.cn>
> > Tested-by: Ma Chenggong <ma.chenggong at zte.com.cn>
>
> [...]
>
> Thanks,
> Brian