[PATCH v3 1/2] Add libfuzzer target to fuzz/x86_instruction_emulator

[PATCH v3 1/2] Add libfuzzer target to fuzz/x86_instruction_emulator

[Tamas K Lengyel]

This target enables integration into oss-fuzz. Changing invalid input return
to -1 as values other then 0/-1 are reserved by libfuzzer. Also adding the
missing __wrap_vsnprintf wrapper which is required for successful oss-fuzz
build.

Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
---
v3: don't include libfuzzer-harness in target 'all' as it requires specific cc
---
 tools/fuzz/x86_instruction_emulator/Makefile    |  6 +++++-
 tools/fuzz/x86_instruction_emulator/fuzz-emul.c |  6 ++----
 tools/tests/x86_emulator/wrappers.c             | 11 +++++++++++
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/tools/fuzz/x86_instruction_emulator/Makefile b/tools/fuzz/x86_instruction_emulator/Makefile
index 1e4c6b37f5..459743f4d9 100644
--- a/tools/fuzz/x86_instruction_emulator/Makefile
+++ b/tools/fuzz/x86_instruction_emulator/Makefile
@@ -58,6 +58,9 @@ afl-harness: afl-harness.o $(OBJS) cpuid.o wrappers.o
 afl-harness-cov: afl-harness-cov.o $(patsubst %.o,%-cov.o,$(OBJS)) cpuid.o wrappers.o
 	$(CC) $(CFLAGS) $(GCOV_FLAGS) $(addprefix -Wl$(comma)--wrap=,$(WRAPPED)) $^ -o $@
 
+libfuzzer-harness: $(OBJS) cpuid.o wrappers.o
+	$(CC) $(CFLAGS) $(LIB_FUZZING_ENGINE) -fsanitize=fuzzer $(addprefix -Wl$(comma)--wrap=,$(WRAPPED)) $^ -o $@
+
 # Common targets
 .PHONY: all
 all: x86-insn-fuzz-all
@@ -67,7 +70,8 @@ distclean: clean
 
 .PHONY: clean
 clean:
-	rm -f *.a *.o $(DEPS_RM) afl-harness afl-harness-cov *.gcda *.gcno *.gcov
+	rm -f *.a *.o $(DEPS_RM) *.gcda *.gcno *.gcov
+	rm -f afl-harness afl-harness-cov libfuzzer-harness
 	rm -rf x86_emulate x86-emulate.c x86-emulate.h wrappers.c cpuid.c
 
 .PHONY: install
diff --git a/tools/fuzz/x86_instruction_emulator/fuzz-emul.c b/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
index eeeb6931f4..2ba9ca9e0b 100644
--- a/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
+++ b/tools/fuzz/x86_instruction_emulator/fuzz-emul.c
@@ -906,14 +906,12 @@ int LLVMFuzzerTestOneInput(const uint8_t *data_p, size_t size)
 
     if ( size <= DATA_OFFSET )
     {
-        printf("Input too small\n");
-        return 1;
+        return -1;
     }
 
     if ( size > FUZZ_CORPUS_SIZE )
     {
-        printf("Input too large\n");
-        return 1;
+        return -1;
     }
 
     memcpy(&input, data_p, size);
diff --git a/tools/tests/x86_emulator/wrappers.c b/tools/tests/x86_emulator/wrappers.c
index 3829a6f416..8f3bd1656f 100644
--- a/tools/tests/x86_emulator/wrappers.c
+++ b/tools/tests/x86_emulator/wrappers.c
@@ -91,6 +91,17 @@ int __wrap_snprintf(char *buf, size_t n, const char *fmt, ...)
     return rc;
 }
 
+int __wrap_vsnprintf(char *buf, size_t n, const char *fmt, va_list varg)
+{
+    int rc;
+
+    emul_save_fpu_state();
+    rc = __real_vsnprintf(buf, n, fmt, varg);
+    emul_restore_fpu_state();
+
+    return rc;
+}
+
 char *__wrap_strstr(const char *s1, const char *s2)
 {
     char *s;
-- 
2.34.1

[PATCH v3 2/2] Add tools/fuzz/oss-fuzz/build.sh

[Tamas K Lengyel]

The build integration script for oss-fuzz targets. Future fuzzing targets can
be added to this script and those targets will be automatically picked up by
oss-fuzz without having to open separate PRs on the oss-fuzz repo.

Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
---
v3: Add Apache-2.0 to LICENSES and use only SPDX on script
---
 LICENSES/Apache-2.0          | 202 +++++++++++++++++++++++++++++++++++
 tools/fuzz/oss-fuzz/build.sh |  11 ++
 2 files changed, 213 insertions(+)
 create mode 100644 LICENSES/Apache-2.0
 create mode 100755 tools/fuzz/oss-fuzz/build.sh

diff --git a/LICENSES/Apache-2.0 b/LICENSES/Apache-2.0
new file mode 100644
index 0000000000..d645695673
--- /dev/null
+++ b/LICENSES/Apache-2.0
@@ -0,0 +1,202 @@
+
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diff --git a/tools/fuzz/oss-fuzz/build.sh b/tools/fuzz/oss-fuzz/build.sh
new file mode 100755
index 0000000000..08eeb66e4c
--- /dev/null
+++ b/tools/fuzz/oss-fuzz/build.sh
@@ -0,0 +1,11 @@
+#!/bin/bash -eu
+# Copyright 2024 Google LLC
+# SPDX-License-Identifier: Apache-2.0
+
+# This script is intended to be run only from the oss-fuzz docker framework
+# See https://google.github.io/oss-fuzz/getting-started/new-project-guide/#buildsh
+cd xen
+./configure --disable-stubdom --disable-pvshim --disable-docs --disable-xen --with-system-qemu
+make clang=y -C tools/include
+make clang=y -C tools/fuzz/x86_instruction_emulator libfuzzer-harness
+cp tools/fuzz/x86_instruction_emulator/libfuzzer-harness $OUT/x86_instruction_emulator
-- 
2.34.1

Re: [PATCH v3 2/2] Add tools/fuzz/oss-fuzz/build.sh

[Jan Beulich]

On 22.07.2024 13:27, Tamas K Lengyel wrote:
> --- /dev/null
> +++ b/LICENSES/Apache-2.0
> @@ -0,0 +1,202 @@
> +
> +                                 Apache License
> +                           Version 2.0, January 2004
> +                        http://www.apache.org/licenses/

Better https:// (also near the end) nowadays?

Other files in this directory also have at least one Valid-License-Identifier:
line and at least one SPDX-URL: one. Depending on what would be put there, I'd
then wonder whether ...

> --- /dev/null
> +++ b/tools/fuzz/oss-fuzz/build.sh
> @@ -0,0 +1,11 @@
> +#!/bin/bash -eu
> +# Copyright 2024 Google LLC
> +# SPDX-License-Identifier: Apache-2.0

... there wouldn't want to be an "-only" tag here. Yet I'm entirely uncertain
with this, as CC-BY-4.0 also has no such tag.

I guess I should offer making respective adjustments while committing. I'll
wait with an ack though to give Alejandro some time to confirm that you
addressed his bash related comment.

Jan

> +# This script is intended to be run only from the oss-fuzz docker framework
> +# See https://google.github.io/oss-fuzz/getting-started/new-project-guide/#buildsh
> +cd xen
> +./configure --disable-stubdom --disable-pvshim --disable-docs --disable-xen --with-system-qemu
> +make clang=y -C tools/include
> +make clang=y -C tools/fuzz/x86_instruction_emulator libfuzzer-harness
> +cp tools/fuzz/x86_instruction_emulator/libfuzzer-harness $OUT/x86_instruction_emulator

Re: [PATCH v3 2/2] Add tools/fuzz/oss-fuzz/build.sh

[Tamas K Lengyel]

On Mon, Jul 22, 2024 at 8:20 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 22.07.2024 13:27, Tamas K Lengyel wrote:
> > --- /dev/null
> > +++ b/LICENSES/Apache-2.0
> > @@ -0,0 +1,202 @@
> > +
> > +                                 Apache License
> > +                           Version 2.0, January 2004
> > +                        http://www.apache.org/licenses/
>
> Better https:// (also near the end) nowadays?

This is a copy of https://www.apache.org/licenses/LICENSE-2.0.txt and
I'm not going to start modifying it even for such trivial reasons.


> Other files in this directory also have at least one Valid-License-Identifier:
> line and at least one SPDX-URL: one.

I didn't notice but should be trivial to add.

Tamas

Re: [PATCH v3 2/2] Add tools/fuzz/oss-fuzz/build.sh

[Anthony PERARD]

On Mon, Jul 22, 2024 at 02:20:21PM +0200, Jan Beulich wrote:
> On 22.07.2024 13:27, Tamas K Lengyel wrote:
> > +# SPDX-License-Identifier: Apache-2.0
> 
> ... there wouldn't want to be an "-only" tag here. Yet I'm entirely uncertain
> with this, as CC-BY-4.0 also has no such tag.

FYI, all valid SPDX identifier are listed there:
https://spdx.org/licenses/

"Apache-2.0" is the correct one to use.

Cheers,

-- 

Anthony Perard | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech

Re: [PATCH v3 1/2] Add libfuzzer target to fuzz/x86_instruction_emulator

[Jan Beulich]

On 22.07.2024 13:27, Tamas K Lengyel wrote:
> This target enables integration into oss-fuzz. Changing invalid input return
> to -1 as values other then 0/-1 are reserved by libfuzzer. Also adding the
> missing __wrap_vsnprintf wrapper which is required for successful oss-fuzz
> build.
> 
> Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
> ---
> v3: don't include libfuzzer-harness in target 'all' as it requires specific cc

With this, how is it going to be built at all? Only by invoking the special
target "manually" as it seems? Which sets this up for easy bit-rotting. I
wonder what others think here ...

Jan

Re: [PATCH v3 1/2] Add libfuzzer target to fuzz/x86_instruction_emulator

[Tamas K Lengyel]

On Mon, Jul 22, 2024 at 8:24 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 22.07.2024 13:27, Tamas K Lengyel wrote:
> > This target enables integration into oss-fuzz. Changing invalid input return
> > to -1 as values other then 0/-1 are reserved by libfuzzer. Also adding the
> > missing __wrap_vsnprintf wrapper which is required for successful oss-fuzz
> > build.
> >
> > Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
> > ---
> > v3: don't include libfuzzer-harness in target 'all' as it requires specific cc
>
> With this, how is it going to be built at all? Only by invoking the special
> target "manually" as it seems? Which sets this up for easy bit-rotting. I
> wonder what others think here ...

Yes, by calling make with the specific target. It's not going to
bitrot because oss-fuzz will pick up any regression on a daily basis
to this target. I assume you would be interested in receiving the
fuzzing reports so it would show as a build failure in case something
broke it.

Tamas

Re: [PATCH v3 1/2] Add libfuzzer target to fuzz/x86_instruction_emulator

[Jan Beulich]

On 22.07.2024 15:51, Tamas K Lengyel wrote:
> On Mon, Jul 22, 2024 at 8:24 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 22.07.2024 13:27, Tamas K Lengyel wrote:
>>> This target enables integration into oss-fuzz. Changing invalid input return
>>> to -1 as values other then 0/-1 are reserved by libfuzzer. Also adding the
>>> missing __wrap_vsnprintf wrapper which is required for successful oss-fuzz
>>> build.
>>>
>>> Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
>>> ---
>>> v3: don't include libfuzzer-harness in target 'all' as it requires specific cc
>>
>> With this, how is it going to be built at all? Only by invoking the special
>> target "manually" as it seems? Which sets this up for easy bit-rotting. I
>> wonder what others think here ...
> 
> Yes, by calling make with the specific target. It's not going to
> bitrot because oss-fuzz will pick up any regression on a daily basis
> to this target. I assume you would be interested in receiving the
> fuzzing reports so it would show as a build failure in case something
> broke it.

Please forgive my lack of knowledge here, but which part of whose
infrastructure would pick up stuff in a daily basis, and what fuzzing
reports (I've never seen any, daily or not) are you talking about?
For now it feels to me as if you're talking of what's possible down
the road, not what's going to happen from the moment this patch was
committed in a 2nd try. If so, the gap between both points in time
may be significant, and hence my bit-rotting concern would still
apply.

Jan

Re: [PATCH v3 1/2] Add libfuzzer target to fuzz/x86_instruction_emulator

[Tamas K Lengyel]

On Mon, Jul 22, 2024 at 9:57 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 22.07.2024 15:51, Tamas K Lengyel wrote:
> > On Mon, Jul 22, 2024 at 8:24 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 22.07.2024 13:27, Tamas K Lengyel wrote:
> >>> This target enables integration into oss-fuzz. Changing invalid input return
> >>> to -1 as values other then 0/-1 are reserved by libfuzzer. Also adding the
> >>> missing __wrap_vsnprintf wrapper which is required for successful oss-fuzz
> >>> build.
> >>>
> >>> Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
> >>> ---
> >>> v3: don't include libfuzzer-harness in target 'all' as it requires specific cc
> >>
> >> With this, how is it going to be built at all? Only by invoking the special
> >> target "manually" as it seems? Which sets this up for easy bit-rotting. I
> >> wonder what others think here ...
> >
> > Yes, by calling make with the specific target. It's not going to
> > bitrot because oss-fuzz will pick up any regression on a daily basis
> > to this target. I assume you would be interested in receiving the
> > fuzzing reports so it would show as a build failure in case something
> > broke it.
>
> Please forgive my lack of knowledge here, but which part of whose
> infrastructure would pick up stuff in a daily basis, and what fuzzing
> reports (I've never seen any, daily or not) are you talking about?
> For now it feels to me as if you're talking of what's possible down
> the road, not what's going to happen from the moment this patch was
> committed in a 2nd try. If so, the gap between both points in time
> may be significant, and hence my bit-rotting concern would still
> apply.

Once these two patches are merged to Xen I'll send my PR to oss-fuzz
to have it pull Xen daily and build this fuzzer and run it on their
infrastructure. It usually takes them less than 24 hours to respond to
PRs, I have added multiple projects there already so the "lag" you
worry about it's not something to worry about.

Having these two patches upstream in Xen is not required by the way, I
could just send these to be upstream to oss-fuzz and have them apply
them after it pulling the xen git repo but it gives more flexibility
to you guys to add additional fuzzers in the future more easily if
these are in your repository because you don't even have to touch
oss-fuzz afterwards.

If you need to learn more about what oss-fuzz is and how it operates
they have a quite nice documentation.

Tamas