Date: Mon, 25 Jul 2016 10:50:05 -0700 From: Kees Cook <keescook@...omium.org> To: Laura Abbott <labbott@...hat.com> Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, 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" <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-arm-kernel@...ts.infradead.org>, linux-ia64@...r.kernel.org, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, sparclinux <sparclinux@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v4 00/12] mm: Hardened usercopy On Fri, Jul 22, 2016 at 5:36 PM, Laura Abbott <labbott@...hat.com> wrote: > 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. Yeah, there is an entire section of tests in lkdtm for the usercopy protection. I didn't add anything for CMA or multipage allocations yet, though. Feel free to add those if you have a moment! :) It's on my todo list. -Kees -- Kees Cook Chrome OS & Brillo Security
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