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 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
