* Dave Hansen <dave@xxxxxxxx> wrote:
> On 10/01/2015 01:39 PM, Kees Cook wrote:
> > On Thu, Oct 1, 2015 at 4:17 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> >> So could we try to add an (opt-in) kernel option that enables this transparently
> >> and automatically for all PROT_EXEC && !PROT_WRITE mappings, without any
> >> user-space changes and syscalls necessary?
> >
> > I would like this very much. :)
>
> Here it is in a quite fugly form (well, it's not opt-in). Init crashes
> if I boot with this, though.
>
> I'll see if I can turn it in to a bit more of an opt-in and see what's
> actually going wrong.
So the reality of modern Linux distros is that, according to some limited
strace-ing around, pure PROT_EXEC usage does not seem to exist: 99% of executable
mappings are mapped via PROT_EXEC|PROT_READ.
So the most usable kernel testing approach would be to enable these types of pkeys
for a child task via some mechanism and inherit it to all children (including
inheriting it over non-suid exec) - but not to any other task.
You could hijack a new personality bit just for debug purposes - see the (totally
untested) patch below.
Depending on user-space's assumptions it might not end up being anything usable we
can apply, but it would be a great testing tool if it worked to a certain degree.
I.e. allow the system to boot in without pkeys set for any task, then set the
personality of a shell process to PER_LINUX_PKEYS and see which binaries (if any!)
will start up without segfaulting.
This way you don't have to debug SystemD, which is extremely fragile and
passive-aggressive towards kernels that don't behave in precisely the fashion
under which SystemD is being developed.
Thanks,
Ingo
========>
Absolutely-Not-Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
include/uapi/linux/personality.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/include/uapi/linux/personality.h b/include/uapi/linux/personality.h
index aa169c4339d2..bead47213419 100644
--- a/include/uapi/linux/personality.h
+++ b/include/uapi/linux/personality.h
@@ -8,6 +8,7 @@
* These occupy the top three bytes.
*/
enum {
+ PROT_READ_EXEC_HACK = 0x0010000, /* PROT_READ|PROT_EXEC == PROT_EXEC hack */
UNAME26 = 0x0020000,
ADDR_NO_RANDOMIZE = 0x0040000, /* disable randomization of VA space */
FDPIC_FUNCPTRS = 0x0080000, /* userspace function ptrs point to descriptors
@@ -41,6 +42,7 @@ enum {
enum {
PER_LINUX = 0x0000,
PER_LINUX_32BIT = 0x0000 | ADDR_LIMIT_32BIT,
+ PER_LINUX_PKEYS = 0x0000 | PROT_READ_EXEC_HACK,
PER_LINUX_FDPIC = 0x0000 | FDPIC_FUNCPTRS,
PER_SVR4 = 0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO,
PER_SVR3 = 0x0002 | STICKY_TIMEOUTS | SHORT_INODE,
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