lkml.org 
[lkml]   [2015]   [Apr]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: regression from your recent change to x86's copy_user_handle_tail()
From
On Tue, Apr 21, 2015 at 11:33 PM, Jan Beulich <JBeulich@suse.com> wrote:
>
> while the description of commit cae2a173fe certainly makes sense, the
> change itself ignores the __probe_kernel_write() code path, for which
> the destination address is expected to be in kernel space but accesses
> may still fault. I.e. the use of plain memset() causes
> __probe_kernel_write() to oops rather than return an error. Shouldn't
> the "(unsigned long)to >= TASK_SIZE_MAX" be relaxed to take the
> effect of set_fs() into account?

Hmm. I think you're right. So something like

--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -82,7 +82,7 @@ copy_user_handle_tail(char *to, char *from, unsigned len)
clac();

/* If the destination is a kernel buffer, we always clear the end */
- if ((unsigned long)to >= TASK_SIZE_MAX)
+ if (!__addr_ok(to))
memset(to, 0, len);
return len;
}

which will effectively say "only if we copy from user mode to kernel
mode" because if we use "set_fs(KERNEL_DS)" then kernel addresses will
also be __addr_ok..

Did you have a test-case for this? I guess we're talking odd ftrace
uses or kgdb?

Linus


\
 
 \ /
  Last update: 2015-04-23 18:01    [W:0.075 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site