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* [PATCH -next] kasan: fix -Wstringop-overflow warning
@ 2020-03-11 13:42 ` Walter Wu
  0 siblings, 0 replies; 6+ messages in thread
From: Walter Wu @ 2020-03-11 13:42 UTC (permalink / raw)
  To: Andrey Ryabinin, Alexander Potapenko, Dmitry Vyukov, Qian Cai,
	Andrew Morton, Stephen Rothwell
  Cc: kasan-dev, linux-mm, linux-kernel, linux-arm-kernel,
	wsd_upstream, Walter Wu

Compiling with gcc-9.2.1 points out below warnings.

In function 'memmove',
    inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
include/linux/string.h:441:9: warning: '__builtin_memmove' specified
bound 18446744073709551614 exceeds maximum object size
9223372036854775807 [-Wstringop-overflow=]

Why generate this warnings?
Because our test function deliberately pass a negative number in memmove(),
so we need to make it "volatile" so that compiler doesn't see it.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
---
 lib/test_kasan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index f123b4b8aadf..e3087d90e00d 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
 {
 	char *ptr;
 	size_t size = 64;
+	volatile size_t invalid_size = -2;
 
 	pr_info("invalid size in memmove\n");
 	ptr = kmalloc(size, GFP_KERNEL);
@@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
 	}
 
 	memset((char *)ptr, 0, 64);
-	memmove((char *)ptr, (char *)ptr + 4, -2);
+	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
 	kfree(ptr);
 }
 
-- 
2.18.0

^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [PATCH -next] kasan: fix -Wstringop-overflow warning
@ 2020-03-11 13:42 ` Walter Wu
  0 siblings, 0 replies; 6+ messages in thread
From: Walter Wu @ 2020-03-11 13:42 UTC (permalink / raw)
  To: Andrey Ryabinin, Alexander Potapenko, Dmitry Vyukov, Qian Cai,
	Andrew Morton, Stephen Rothwell
  Cc: Walter Wu, wsd_upstream, linux-kernel, kasan-dev, linux-mm,
	linux-arm-kernel

Compiling with gcc-9.2.1 points out below warnings.

In function 'memmove',
    inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
include/linux/string.h:441:9: warning: '__builtin_memmove' specified
bound 18446744073709551614 exceeds maximum object size
9223372036854775807 [-Wstringop-overflow=]

Why generate this warnings?
Because our test function deliberately pass a negative number in memmove(),
so we need to make it "volatile" so that compiler doesn't see it.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
---
 lib/test_kasan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index f123b4b8aadf..e3087d90e00d 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
 {
 	char *ptr;
 	size_t size = 64;
+	volatile size_t invalid_size = -2;
 
 	pr_info("invalid size in memmove\n");
 	ptr = kmalloc(size, GFP_KERNEL);
@@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
 	}
 
 	memset((char *)ptr, 0, 64);
-	memmove((char *)ptr, (char *)ptr + 4, -2);
+	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
 	kfree(ptr);
 }
 
-- 
2.18.0
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [PATCH -next] kasan: fix -Wstringop-overflow warning
  2020-03-11 13:42 ` Walter Wu
@ 2020-03-11 23:38   ` Andrew Morton
  -1 siblings, 0 replies; 6+ messages in thread
From: Andrew Morton @ 2020-03-11 23:38 UTC (permalink / raw)
  To: Walter Wu
  Cc: Andrey Ryabinin, Alexander Potapenko, Dmitry Vyukov, Qian Cai,
	Stephen Rothwell, kasan-dev, linux-mm, linux-kernel,
	linux-arm-kernel, wsd_upstream

On Wed, 11 Mar 2020 21:42:44 +0800 Walter Wu <walter-zh.wu@mediatek.com> wrote:

> Compiling with gcc-9.2.1 points out below warnings.
> 
> In function 'memmove',
>     inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
> include/linux/string.h:441:9: warning: '__builtin_memmove' specified
> bound 18446744073709551614 exceeds maximum object size
> 9223372036854775807 [-Wstringop-overflow=]
> 
> Why generate this warnings?
> Because our test function deliberately pass a negative number in memmove(),
> so we need to make it "volatile" so that compiler doesn't see it.
> 
> ...
>
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
>  {
>  	char *ptr;
>  	size_t size = 64;
> +	volatile size_t invalid_size = -2;
>  
>  	pr_info("invalid size in memmove\n");
>  	ptr = kmalloc(size, GFP_KERNEL);
> @@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
>  	}
>  
>  	memset((char *)ptr, 0, 64);
> -	memmove((char *)ptr, (char *)ptr + 4, -2);
> +	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
>  	kfree(ptr);
>  }

Huh.  Why does this trick suppress the warning?

Do we have any guarantee that this it will contiue to work in future
gcc's?



^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH -next] kasan: fix -Wstringop-overflow warning
@ 2020-03-11 23:38   ` Andrew Morton
  0 siblings, 0 replies; 6+ messages in thread
From: Andrew Morton @ 2020-03-11 23:38 UTC (permalink / raw)
  To: Walter Wu
  Cc: Stephen Rothwell, wsd_upstream, linux-kernel, kasan-dev,
	linux-mm, Qian Cai, linux-arm-kernel, Andrey Ryabinin,
	Alexander Potapenko, Dmitry Vyukov

On Wed, 11 Mar 2020 21:42:44 +0800 Walter Wu <walter-zh.wu@mediatek.com> wrote:

> Compiling with gcc-9.2.1 points out below warnings.
> 
> In function 'memmove',
>     inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
> include/linux/string.h:441:9: warning: '__builtin_memmove' specified
> bound 18446744073709551614 exceeds maximum object size
> 9223372036854775807 [-Wstringop-overflow=]
> 
> Why generate this warnings?
> Because our test function deliberately pass a negative number in memmove(),
> so we need to make it "volatile" so that compiler doesn't see it.
> 
> ...
>
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
>  {
>  	char *ptr;
>  	size_t size = 64;
> +	volatile size_t invalid_size = -2;
>  
>  	pr_info("invalid size in memmove\n");
>  	ptr = kmalloc(size, GFP_KERNEL);
> @@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
>  	}
>  
>  	memset((char *)ptr, 0, 64);
> -	memmove((char *)ptr, (char *)ptr + 4, -2);
> +	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
>  	kfree(ptr);
>  }

Huh.  Why does this trick suppress the warning?

Do we have any guarantee that this it will contiue to work in future
gcc's?



_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH -next] kasan: fix -Wstringop-overflow warning
  2020-03-11 23:38   ` Andrew Morton
@ 2020-03-12  5:03     ` Walter Wu
  -1 siblings, 0 replies; 6+ messages in thread
From: Walter Wu @ 2020-03-12  5:03 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Andrey Ryabinin, Alexander Potapenko, Dmitry Vyukov, Qian Cai,
	Stephen Rothwell, kasan-dev, linux-mm, linux-kernel,
	linux-arm-kernel, wsd_upstream

On Wed, 2020-03-11 at 16:38 -0700, Andrew Morton wrote:
> On Wed, 11 Mar 2020 21:42:44 +0800 Walter Wu <walter-zh.wu@mediatek.com> wrote:
> 
> > Compiling with gcc-9.2.1 points out below warnings.
> > 
> > In function 'memmove',
> >     inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
> > include/linux/string.h:441:9: warning: '__builtin_memmove' specified
> > bound 18446744073709551614 exceeds maximum object size
> > 9223372036854775807 [-Wstringop-overflow=]
> > 
> > Why generate this warnings?
> > Because our test function deliberately pass a negative number in memmove(),
> > so we need to make it "volatile" so that compiler doesn't see it.
> > 
> > ...
> >
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
> >  {
> >  	char *ptr;
> >  	size_t size = 64;
> > +	volatile size_t invalid_size = -2;
> >  
> >  	pr_info("invalid size in memmove\n");
> >  	ptr = kmalloc(size, GFP_KERNEL);
> > @@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
> >  	}
> >  
> >  	memset((char *)ptr, 0, 64);
> > -	memmove((char *)ptr, (char *)ptr + 4, -2);
> > +	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
> >  	kfree(ptr);
> >  }
> 
> Huh.  Why does this trick suppress the warning?
> 
We read below the document, so we try to verify whether it is work for
another checking. After we changed the code, It is ok.

https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Warning-Options.html#Warning-Options
"They do not occur for variables or elements declared volatile. Because
these warnings depend on optimization, the exact variables or elements
for which there are warnings depends on the precise optimization options
and version of GCC used."

> Do we have any guarantee that this it will contiue to work in future
> gcc's?
> 
Sorry, I am not compiler expert, so I can't guarantee gcc will not
modify the rule, but at least it is work before gcc-9.
> 


^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH -next] kasan: fix -Wstringop-overflow warning
@ 2020-03-12  5:03     ` Walter Wu
  0 siblings, 0 replies; 6+ messages in thread
From: Walter Wu @ 2020-03-12  5:03 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Stephen Rothwell, wsd_upstream, linux-kernel, kasan-dev,
	linux-mm, Qian Cai, linux-arm-kernel, Andrey Ryabinin,
	Alexander Potapenko, Dmitry Vyukov

On Wed, 2020-03-11 at 16:38 -0700, Andrew Morton wrote:
> On Wed, 11 Mar 2020 21:42:44 +0800 Walter Wu <walter-zh.wu@mediatek.com> wrote:
> 
> > Compiling with gcc-9.2.1 points out below warnings.
> > 
> > In function 'memmove',
> >     inlined from 'kmalloc_memmove_invalid_size' at lib/test_kasan.c:301:2:
> > include/linux/string.h:441:9: warning: '__builtin_memmove' specified
> > bound 18446744073709551614 exceeds maximum object size
> > 9223372036854775807 [-Wstringop-overflow=]
> > 
> > Why generate this warnings?
> > Because our test function deliberately pass a negative number in memmove(),
> > so we need to make it "volatile" so that compiler doesn't see it.
> > 
> > ...
> >
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -289,6 +289,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
> >  {
> >  	char *ptr;
> >  	size_t size = 64;
> > +	volatile size_t invalid_size = -2;
> >  
> >  	pr_info("invalid size in memmove\n");
> >  	ptr = kmalloc(size, GFP_KERNEL);
> > @@ -298,7 +299,7 @@ static noinline void __init kmalloc_memmove_invalid_size(void)
> >  	}
> >  
> >  	memset((char *)ptr, 0, 64);
> > -	memmove((char *)ptr, (char *)ptr + 4, -2);
> > +	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
> >  	kfree(ptr);
> >  }
> 
> Huh.  Why does this trick suppress the warning?
> 
We read below the document, so we try to verify whether it is work for
another checking. After we changed the code, It is ok.

https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Warning-Options.html#Warning-Options
"They do not occur for variables or elements declared volatile. Because
these warnings depend on optimization, the exact variables or elements
for which there are warnings depends on the precise optimization options
and version of GCC used."

> Do we have any guarantee that this it will contiue to work in future
> gcc's?
> 
Sorry, I am not compiler expert, so I can't guarantee gcc will not
modify the rule, but at least it is work before gcc-9.
> 

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-03-12  5:07 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-11 13:42 [PATCH -next] kasan: fix -Wstringop-overflow warning Walter Wu
2020-03-11 13:42 ` Walter Wu
2020-03-11 23:38 ` Andrew Morton
2020-03-11 23:38   ` Andrew Morton
2020-03-12  5:03   ` Walter Wu
2020-03-12  5:03     ` Walter Wu

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