On Fri, 2016-07-15 at 14:44 -0700, Kees Cook wrote:

Hi,
?
[I'm going to carry this series in my kspp -next tree now, though I'd
really love to have some explicit Acked-bys or Reviewed-bys. If you've
looked through it or tested it, please consider it. :) (I added Valdis
and mpe's Tested-bys where they seemed correct, thank you!)]
?
This is a start of the mainline port of PAX_USERCOPY[1]. After I started
writing tests (now in lkdtm in -next) for Casey's earlier port[2], I kept
tweaking things further and further until I ended up with a whole new
patch series. To that end, I took Rik and other people's feedback along
with other changes and clean-ups.
?
Based on my understanding, PAX_USERCOPY was designed to catch a
few classes of flaws (mainly bad bounds checking) around the use of
copy_to_user()/copy_from_user(). These changes don't touch get_user() and
put_user(), since these operate on constant sized lengths, and tend to be
much less vulnerable. There are effectively three distinct protections in
the whole series, each of which I've given a separate CONFIG, though this
patch set is only the first of the three intended protections. (Generally
speaking, PAX_USERCOPY covers what I'm calling CONFIG_HARDENED_USERCOPY
(this) and CONFIG_HARDENED_USERCOPY_WHITELIST (future), and
PAX_USERCOPY_SLABS covers CONFIG_HARDENED_USERCOPY_SPLIT_KMALLOC
(future).)
?
This series, which adds CONFIG_HARDENED_USERCOPY, checks that objects
being copied to/from userspace meet certain criteria:
- if address is a heap object, the size must not exceed the object's
? allocated size. (This will catch all kinds of heap overflow flaws.)
- if address range is in the current process stack, it must be within the
? current stack frame (if such checking is possible) or at least entirely
? within the current process's stack. (This could catch large lengths that
? would have extended beyond the current process stack, or overflows if
? their length extends back into the original stack.)
- if the address range is part of kernel data, rodata, or bss, allow it.
- if address range is page-allocated, that it doesn't span multiple
? allocations.
- if address is within the kernel text, reject it.
- everything else is accepted
?
The patches in the series are:
- Support for arch-specific stack frame checking (which will likely be
? replaced in the future by Josh's more comprehensive unwinder):
????????1- mm: Implement stack frame object validation
- The core copy_to/from_user() checks, without the slab object checks:
????????2- mm: Hardened usercopy
- Per-arch enablement of the protection:
????????3- x86/uaccess: Enable hardened usercopy
????????4- ARM: uaccess: Enable hardened usercopy
????????5- arm64/uaccess: Enable hardened usercopy
????????6- ia64/uaccess: Enable hardened usercopy
????????7- powerpc/uaccess: Enable hardened usercopy
????????8- sparc/uaccess: Enable hardened usercopy
????????9- s390/uaccess: Enable hardened usercopy
- The heap allocator implementation of object size checking:
???????10- mm: SLAB hardened usercopy support
???????11- mm: SLUB hardened usercopy support
?
Some notes:
?
- This is expected to apply on top of -next which contains fixes for the
? position of _etext on both arm and arm64, though it has minor conflicts
? with KASAN that are trivial to fix up. Living in -next are also tests
? for this protection in lkdtm, prefixed with USERCOPY_.
?
- I couldn't detect a measurable performance change with these features
? enabled. Kernel build times were unchanged, hackbench was unchanged,
? etc. I think we could flip this to "on by default" at some point, but
? for now, I'm leaving it off until I can get some more definitive
? measurements. I would love if someone with greater familiarity with
? perf could give this a spin and report results.
?
- The SLOB support extracted from grsecurity seems entirely broken. I
? have no idea what's going on there, I spent my time testing SLAB and
? SLUB. Having someone else look at SLOB would be nice, but this series
? doesn't depend on it.
?
Additional features that would be nice, but aren't blocking this series:
?
- Needs more architecture support for stack frame checking (only x86 now,
? but it seems Josh will have a good solution for this soon).
?
?
Thanks!
?
-Kees
?
[1] https://grsecurity.net/download.php "grsecurity - test kernel patch"
[2] http://www.openwall.com/lists/kernel-hardening/2016/05/19/5
?
v3:
- switch to using BUG for better Oops integration
- when checking page allocations, check each for Reserved
- use enums for the stack check return for readability

Thanks looks good so far! I'll try and test it and report back

Balbir?