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Fork-fuzzing provides a few pros, but our implementation prevents us
from using fuzzers other than libFuzzer, and may be causing issues such
as coverage-failure builds on OSS-Fuzz. It is not a great long-term
solution as it depends on internal implementation details of libFuzzer
(which is no longer in active development). Remove it in favor of other
methods of resetting state between inputs.
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
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LLVM's linker, LLD, supports the keyword "INSERT AFTER", starting with
version 11.
However, when multiple sections are defined in the same "INSERT AFTER",
they are added in a reversed order, compared to BFD's LD.
This patch makes fork_fuzz.ld generic enough to work with both linkers.
Each section now has its own "INSERT AFTER" keyword, so proper ordering is
defined between the sections added.
Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
Message-Id: <20201105221905.1350-2-dbuono@linux.vnet.ibm.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Thomas Huth <thuth@redhat.com>
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Previously, we relied on "FuzzerTracePC*(.bss*)" to place libfuzzer's
fuzzer::TPC object into our contiguous shared-memory region. This does
not work for some libfuzzer builds, so this addition identifies the
region by its mangled name: *(.bss._ZN6fuzzer3TPCE);
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20200512030133.29896-4-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20200227031439.31386-2-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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fork() is a simple way to ensure that state does not leak in between
fuzzing runs. Unfortunately, the fuzzer mutation engine relies on
bitmaps which contain coverage information for each fuzzing run, and
these bitmaps should be copied from the child to the parent(where the
mutation occurs). These bitmaps are created through compile-time
instrumentation and they are not shared with fork()-ed processes, by
default. To address this, we create a shared memory region, adjust its
size and map it _over_ the counter region. Furthermore, libfuzzer
doesn't generally expose the globals that specify the location of the
counters/coverage bitmap. As a workaround, we rely on a custom linker
script which forces all of the bitmaps we care about to be placed in a
contiguous region, which is easy to locate and mmap over.
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20200220041118.23264-16-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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