[PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

Andy Lutomirski
2016-06-20T23:45:12Z

Since the dawn of time, a kernel stack overflow has been a real PITA
to debug, has caused nondeterministic crashes some time after the
actual overflow, and has generally been easy to exploit for root.

With this series, arches can enable HAVE_ARCH_VMAP_STACK. Arches
that enable it (just x86 for now) get virtually mapped stacks with
guard pages. This causes reliable faults when the stack overflows.

If the arch implements it well, we get a nice OOPS on stack overflow
(as opposed to panicing directly or otherwise exploding badly). On
x86, the OOPS is nice, has a usable call trace, and the overflowing
task is killed cleanly.

On my laptop, this adds about 1.5µs of overhead to task creation,
which seems to be mainly caused by vmalloc inefficiently allocating
individual pages even when a higher-order page is available on the
freelist.

This does not address interrupt stacks. It also does not address
the possibility of privilege escalation by a controlled stack
overflow that overwrites thread_info without hitting the guard page.
I'll send patches to address the latter issue once this series
lands.

It's worth noting that s390 has an arch-specific gcc feature that
detects stack overflows by adjusting function prologues. Arches
with features like that may wish to avoid using vmapped stacks to
minimize the performance hit.

Ingo, would it make sense to throw it into a seaparate branch in
-tip? I wouldn't mind seeing some -next testing to give people a
chance to shake out problems. I'm particularly interested in
whether there are any drivers that expect virt_to_phys to work on
stack addresses. (I know that virtio-net used to, but I fixed that
a while back.)

Changes from v2:
- Delete kerne_unmap_pages_in_pgd rather than hardening it (Borislav)
- Fix sub-page stack accounting better (Josh)

Changes from v1:
- Fix rewind_stack_and_do_exit (Josh)
- Fix deadlock under load
- Clean up generic stack vmalloc code
- Many other minor fixes

Andy Lutomirski (12):
x86/cpa: In populate_pgd, don't set the pgd entry until it's populated
x86/mm: Remove kernel_unmap_pages_in_pgd() and
efi_cleanup_page_tables()
mm: Track NR_KERNEL_STACK in KiB instead of number of stacks
mm: Fix memcg stack accounting for sub-page stacks
fork: Add generic vmalloced stack support
x86/die: Don't try to recover from an OOPS on a non-default stack
x86/dumpstack: When OOPSing, rewind the stack before do_exit
x86/dumpstack: When dumping stack bytes due to OOPS, start with
regs->sp
x86/dumpstack: Try harder to get a call trace on stack overflow
x86/dumpstack/64: Handle faults when printing the "Stack:" part of an
OOPS
x86/mm/64: Enable vmapped stacks
x86/mm: Improve stack-overflow #PF handling

Ingo Molnar (1):
x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()

arch/Kconfig | 29 ++++++++++++
arch/ia64/include/asm/thread_info.h | 2 +-
arch/x86/Kconfig | 1 +
arch/x86/entry/entry_32.S | 11 +++++
arch/x86/entry/entry_64.S | 11 +++++
arch/x86/include/asm/efi.h | 1 -
arch/x86/include/asm/pgtable_types.h | 2 -
arch/x86/include/asm/switch_to.h | 28 +++++++++++-
arch/x86/include/asm/traps.h | 6 +++
arch/x86/kernel/dumpstack.c | 19 +++++++-
arch/x86/kernel/dumpstack_32.c | 4 +-
arch/x86/kernel/dumpstack_64.c | 16 +++++--
arch/x86/kernel/traps.c | 32 ++++++++++++++
arch/x86/mm/fault.c | 39 ++++++++++++++++
arch/x86/mm/init_64.c | 27 -----------
arch/x86/mm/pageattr.c | 32 ++------------
arch/x86/mm/tlb.c | 15 +++++++
arch/x86/platform/efi/efi.c | 2 -
arch/x86/platform/efi/efi_32.c | 3 --
arch/x86/platform/efi/efi_64.c | 5 ---
drivers/base/node.c | 3 +-
fs/proc/meminfo.c | 2 +-
include/linux/memcontrol.h | 2 +-
include/linux/mmzone.h | 2 +-
include/linux/sched.h | 15 +++++++
kernel/fork.c | 86 +++++++++++++++++++++++++++---------
mm/memcontrol.c | 2 +-
mm/page_alloc.c | 3 +-
28 files changed, 295 insertions(+), 105 deletions(-)

--
2.5.5