On Tue, Apr 21, 2015 at 11:33 PM, Jan Beulich <jbeul...@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
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