Date: Wed, 20 Jul 2016 13:26:55 -0700 From: Kees Cook <keescook@...omium.org> To: kernel-hardening@...ts.openwall.com Cc: Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...oraproject.org>, 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: [PATCH v4 00/12] mm: Hardened usercopy 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
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