Re: [PATCH v10 1/3] x86/syscalls: Check address limit on user-mode return
From: Thomas Garnier
Date: Thu Jul 06 2017 - 16:38:28 EST
On Wed, Jun 28, 2017 at 10:52 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
> >> Ensure the address limit is a user-mode segment before returning to
> >> user-mode. Otherwise a process can corrupt kernel-mode memory and elevate
> >> privileges .
> >> The set_fs function sets the TIF_SETFS flag to force a slow path on
> >> return. In the slow path, the address limit is checked to be USER_DS if
> >> needed.
> >> The addr_limit_user_check function is added as a cross-architecture
> >> function to check the address limit.
> >>  https://bugs.chromium.org/p/project-zero/issues/detail?id=990
> >> Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
> > Thanks for reworking this series!
> > The bad state correctly BUGs under the LKDTM test:
> > [ 21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS
> > [ 21.172791] lkdtm: setting bad task size limit
> > [ 21.173742] ------------[ cut here ]------------
> > [ 21.174641] kernel BUG at ./include/linux/syscalls.h:220!
> > ...
> > [ 21.193166] Call Trace:
> > [ 21.193617] ? trace_hardirqs_on_thunk+0x1a/0x1c
> > [ 21.194443] entry_SYSCALL64_slow_path+0x25/0x25
> > Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Is everyone happy with this patch for x86? Does this need anything
Asking again. Additional feedback? Anyone wants to pick-it up?
> Kees Cook
> Pixel Security