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Thu Feb 16 00:10:22 2017 UTC (5 years, 11 months ago) by maya
Branches: MAIN
CVS tags: HEAD
oops, made the markdown worse.

# Tips for using analyzers on NetBSD #

## Address Sanitizer (+UBsan) (preliminary) ##

ASan reports memory violations, and detects many off-by-ones. It seems to produce very high quality reports.

It only needs to be compiled on the resulting binary[1]. It cannot compile static objects so requires some fiddling with makefiles to disable those.

I've been running it on netbsd tests in the following manner[2]:

    cd /usr/src/tests/lib/libc
    env USETOOLS=never MK_SSP=no HAVE_SSP=no CFLAGS="-fno-omit-frame-pointer -O0 -g -ggdb -U_FORTIFY_SOURCE -fsanitize=address -fsanitize=undefined" LDFLAGS="-lasan -lubsan" make -j20

    env ASAN_OPTIONS=alloc_dealloc_mismatch=0 LD_PRELOAD="/usr/lib/ /usr/lib/" atf-run # [3]

    sysctl -w security.pax.aslr.enabled=0 # [4]

1. Seems like this is a cause of worse reports, as in-library functions
are not intercepted.

2. Not even close to canonical commands, should probably be improved.

3. ASAN_OPTIONS=alloc_dealloc_mismatch=0 is because atf-run itself triggers a bug. Should have a look at it so this option doesn't need to be disabled.

4. To workaround "Shadow memory range interleaves with an existing memory mapping. ASan cannot proceed correctly". An alternative is to LD_PRELOAD and LD_LIBRARY_PATH an entirely separate libc, ld.elf_so, etc.

5. ASan can be wrong about which function is faulting, if we're talking about functions internal to the library. Running it on a separate file or in GDB can be helpful. Worth trying if the failure doesn't make sense.

Important note: ASan should not be run on production systems. [It can pose a
security risk](

## Coverity ##

Coverity is a static analyzer.

You can see a part of its output in coverity-updates@, and a lot more
if you go to the website (sign up with your netbsd email or poke someone
for access).

A lot of the reports are about strncpy/strcpy or in code that belongs
to GCC (in the case of userland), you can tackle this by limiting
results to a particular directory (click the folder icon). You can
also sort by issue.

Some suggestions for things to focus on, as there are many defects

- Setuid programs
- Anything kernel
- Stuff that runs as root
- Library or other code you know well already
- Drivers for hardware you actually own and can test

Future ideas:

- GCC could be told to add ASan flags for all shared objects, making it easier to build world with those flags
- We could run all of NetBSD with ASan for some real world tests.
- ASan for kernel? (subr_kmem.c has some flags which do some of the work, could it do more?)
- Fuzzers are cool.

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