Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory debugger.

From: Andrey Ryabinin
Date: Thu Nov 20 2014 - 07:35:38 EST

On 11/20/2014 12:03 PM, Ingo Molnar wrote:
> * Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote:
>> I've counted 16:
>> aab515d (fib_trie: remove potential out of bound access)
>> 984f173 ([SCSI] sd: Fix potential out-of-bounds access)
>> 5e9ae2e (aio: fix use-after-free in aio_migratepage)
>> 2811eba (ipv6: udp packets following an UFO enqueued packet need also
>> be handled by UFO)
>> 057db84 (tracing: Fix potential out-of-bounds in trace_get_user())
>> 9709674 (ipv4: fix a race in ip4_datagram_release_cb())
>> 4e8d213 (ext4: fix use-after-free in ext4_mb_new_blocks)
>> 624483f (mm: rmap: fix use-after-free in __put_anon_vma)
>> 93b7aca (lib/idr.c: fix out-of-bounds pointer dereference)
>> b4903d6 (mm: debugfs: move rounddown_pow_of_two() out from do_fault path)
>> 40eea80 (net: sendmsg: fix NULL pointer dereference)
>> 10ec947 (ipv4: fix buffer overflow in ip_options_compile())
>> dbf20cb2 (f2fs: avoid use invalid mapping of node_inode when evict meta inode)
>> d6d86c0 (mm/balloon_compaction: redesign ballooned pages management)
>> + 2 recently found, seems minor:
>> (sched/numa: Fix out of bounds read in sched_init_numa())
>> (security: smack: fix out-of-bounds access in smk_parse_smack())
>> Note that some functionality is not yet implemented in this
>> patch set. Kasan has possibility to detect out-of-bounds
>> accesses on global/stack variables. Neither
>> kmemcheck/debug_pagealloc or slub_debug could do that.
>>> That's in a 20-year-old code base, so one new minor bug discovered per
>>> three years? Not worth it!
>>> Presumably more bugs will be exposed as more people use kasan on
>>> different kernel configs, but will their number and seriousness justify
>>> the maintenance effort?
>> Yes, AFAIK there are only few users of kasan now, and I guess that
>> only small part of kernel code
>> was covered by it.
>> IMO kasan shouldn't take a lot maintenance efforts, most part of code
>> is isolated and it doesn't
>> have some complex dependencies on in-kernel API.
>> And you could always just poke me, I'd be happy to sort out any issues.
>>> If kasan will permit us to remove kmemcheck/debug_pagealloc/slub_debug
>>> then that tips the balance a little. What's the feasibility of that?
>> I think kasan could replace kmemcheck at some point.
> So that angle sounds interesting, because kmemcheck is
> essentially unmaintained right now: in the last 3 years since
> v3.0 arch/x86/mm/kmemcheck/ has not seen a single kmemcheck
> specific change, only 4 incidental changes.
> kmemcheck is also very architecture bound and somewhat fragile
> due to having to decode instructions, so if generic, compiler
> driven instrumentation can replace it, that would be a plus.

GCC already supports address sanitizer on x86_32/x86_64/arm/arm64/rs6000,
and adding compiler's support for any other architecture is trivial.

Per-arch work on kernel-side maybe is not trivial, but there is nothing complex either.
It's much more simpler then kmemcheck.

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