lkml.org 
[lkml]   [2017]   [Dec]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: Review of KPTI patchset
On Sat, 30 Dec 2017, Thomas Gleixner wrote:
> On Sat, 30 Dec 2017, Mathieu Desnoyers wrote:
> The only asymetry is in the error path of write_ldt() which can leak a half
> allocated page table. But, that's a nasty one because if there is an
> existing LDT mapped, then the pagetable cannot be freed. So yes, it's not
> nice, but harmless and needs some thought to fix.

In fact it's not a leak. It's just memory waste because the pagetable gets
freed when the process exits.

The memory waste is rather simple to fix. Delta patch below.

Thanks,

tglx

8<--------------
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -421,6 +421,14 @@ static int write_ldt(void __user *ptr, u
*/
error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
if (error) {
+ /*
+ * Drop potentially half populated page table if the
+ * mapping code failed and this was the first attempt to
+ * install a LDT. If there is a LDT installed then the LDT
+ * pagetable cannot be freed for obvious reasons.
+ */
+ if (!old_ldt)
+ free_ldt_pgtables(mm);
free_ldt_struct(new_ldt);
goto out_unlock;
}
\
 
 \ /
  Last update: 2017-12-30 23:45    [W:0.080 / U:0.264 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site