Date: Fri, 22 Jul 2016 17:36:33 -0700 From: Laura Abbott <labbott@...hat.com> To: Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com Cc: Balbir Singh <bsingharora@...il.com>, Daniel Micay <danielmicay@...il.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Rik van Riel <riel@...hat.com>, Casey Schaufler <casey@...aufler-ca.com>, PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>, Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Michael Ellerman <mpe@...erman.id.au>, Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, "David S. Miller" <davem@...emloft.net>, x86@...nel.org, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>, Mathias Krause <minipli@...glemail.com>, Jan Kara <jack@...e.cz>, Vitaly Wool <vitalywool@...il.com>, Andrea Arcangeli <aarcange@...hat.com>, Dmitry Vyukov <dvyukov@...gle.com>, linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org, linux-arch@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v4 00/12] mm: Hardened usercopy On 07/20/2016 01:26 PM, Kees Cook wrote: > Hi, > > [This is now in my kspp -next tree, though I'd really love to add some > additional explicit Tested-bys, Reviewed-bys, or Acked-bys. If you've > looked through any part of this or have done any testing, please consider > sending an email with your "*-by:" line. :)] > > This is a start of the mainline port of PAX_USERCOPY. After writing > tests (now in lkdtm in -next) for Casey's earlier port, I kept tweaking > things further and further until I ended up with a whole new patch series. > To that end, I took Rik, Laura, and other people's feedback along with > additional 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 > a valid 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 (excepting Reserved and CMA pages). > - if address is within the kernel text, reject it. > - everything else is accepted > > The patches in the series are: > - Support for examination of CMA page types: > 1- mm: Add is_migrate_cma_page > - Support for arch-specific stack frame checking (which will likely be > replaced in the future by Josh's more comprehensive unwinder): > 2- mm: Implement stack frame object validation > - The core copy_to/from_user() checks, without the slab object checks: > 3- mm: Hardened usercopy > - Per-arch enablement of the protection: > 4- x86/uaccess: Enable hardened usercopy > 5- ARM: uaccess: Enable hardened usercopy > 6- arm64/uaccess: Enable hardened usercopy > 7- ia64/uaccess: Enable hardened usercopy > 8- powerpc/uaccess: Enable hardened usercopy > 9- sparc/uaccess: Enable hardened usercopy > 10- s390/uaccess: Enable hardened usercopy > - The heap allocator implementation of object size checking: > 11- mm: SLAB hardened usercopy support > 12- 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 some conflicts > with KASAN that should be trivial to fix up. Also in -next are the > 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 > >  https://grsecurity.net/download.php "grsecurity - test kernel patch" >  http://www.openwall.com/lists/kernel-hardening/2016/05/19/5 > > v4: > - handle CMA pages, labbott > - update stack checker comments, labbott > - check for vmalloc addresses, labbott > - deal with KASAN in -next changing arm64 copy*user calls > - check for linear mappings at runtime instead of via CONFIG > > 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 > > v2: > - added s390 support > - handle slub red zone > - disallow writes to rodata area > - stack frame walker now CONFIG-controlled arch-specific helper > Do you have/plan to have LKDTM or the like tests for this? I started reviewing the slub code and was about to write some test cases for myself. I did that for CMA as well which is a decent indicator these should all go somewhere. Thanks, Laura
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