On 3/30/2019 5:26 PM, Ben Dooks wrote:
The copy_user_handle_tail() clearly uses both from and to as pointers
to user-space memory. This triggers sparse warning on using the calls
to get and put to user-space. This can be fixed easily by changing the
call to take __user annotated pointer.s
arch/x86/lib/usercopy_64.c:68:21: warning: incorrect type in argument 1
(different address spaces)
arch/x86/lib/usercopy_64.c:68:21: expected void const volatile [noderef]
<asn:1>*<noident>
arch/x86/lib/usercopy_64.c:68:21: got char *
arch/x86/lib/usercopy_64.c:70:21: warning: incorrect type in argument 1
(different address spaces)
arch/x86/lib/usercopy_64.c:70:21: expected void const volatile [noderef]
<asn:1>*<noident>
arch/x86/lib/usercopy_64.c:70:21: got char *to
From Linus Torvalds:
On Thu, Mar 28, 2019 at 12:24 AM Borislav Petkov <b...@alien8.de> wrote:
Well, but copy_user_generic() (which ends up calling the
copy_user_handle_tail() eventually) casts those __user pointers to
(__force void *). Converting them back to __user looks strange to me.
Linus?
Well, it does that because the x86 version of copy_user_generic() can
work in either direction, so it works when either the source or
destination (or both) are user pointers, but they don't _have_ to be.
So the "userness" of a pointer in that context is a bit ambiguous, and
so we've picked the pointers to be just plain "void *".
That said, arguably we should have gone the other way and just made
them both "__user" pointers, and do the cast the other way around.
But there's no absolutely right answer here, and nobody should ever
use copy_user_generic() directly (ie it is very much meant to be only
used as a internal helper for the cases that get the pointer
annotations right).
Signed-off-by: Ben Dooks <ben.do...@codethink.co.uk>
Reviewed-by: Mukesh Ojha <mo...@codeaurora.org>
Cheers,
-Mukesh
---
arch/x86/include/asm/uaccess_64.h | 2 +-
arch/x86/lib/usercopy_64.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/uaccess_64.h
b/arch/x86/include/asm/uaccess_64.h
index a9d637bc301d..cbca2cb28939 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -208,7 +208,7 @@ __copy_from_user_flushcache(void *dst, const void __user
*src, unsigned size)
}
unsigned long
-copy_user_handle_tail(char *to, char *from, unsigned len);
+copy_user_handle_tail(char __user *to, char __user *from, unsigned len);
unsigned long
mcsafe_handle_tail(char *to, char *from, unsigned len);
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index ee42bb0cbeb3..aa180424e77a 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -60,7 +60,7 @@ EXPORT_SYMBOL(clear_user);
* it is not necessary to optimize tail handling.
*/
__visible unsigned long
-copy_user_handle_tail(char *to, char *from, unsigned len)
+copy_user_handle_tail(char __user *to, char __user *from, unsigned len)
{
for (; len; --len, to++) {
char c;
