contrib: add extract-handshakes kprobe example

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

.gitignore

@@ -20,3 +20,4 @@ src/tests/qemu/distfiles/
 *.nam
 *.til
 *.pro.user
+.cache.mk

contrib/extract-handshakes/.gitignore

@@ -0,0 +1,3 @@
+offset-finder.o
+offset-finder
+offsets.include

contrib/extract-handshakes/Makefile

@@ -0,0 +1,28 @@
+ifeq ($(KERNELRELEASE),)
+KERNELDIR ?= /lib/modules/$(shell uname -r)/build
+PWD := $(shell pwd)
+CFLAGS ?= -O3 -march=native
+CFLAGS += -Wall -pedantic -std=gnu11
+
+offsets.include: offset-finder
+	./$^ > $@
+
+offset-finder: offset-finder.c offset-finder.o
+	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ $^
+
+offset-finder.o: offset-finder.c
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) $@
+	objcopy -j '.rodata*' $@ $@
+
+clean:
+	rm -f offset-finder offsets.include
+	$(MAKE) -C $(KERNELDIR) M=$(PWD) clean
+
+.PHONY: clean
+else
+offset-finder-m := offset-finder.o
+oldsrc := $(src)
+src := $(src)/../../../src
+include $(src)/compat/Kbuild.include
+src := $(oldsrc)
+endif

contrib/extract-handshakes/README

@@ -0,0 +1,20 @@
+Handshake Extractor
+===================
+
+This will extract private keys from outgoing handshake sessions, prior
+to them being sent, via kprobes. It exports the bare minimum to be
+able to then decrypt all packets in the handshake and in the subsequent
+transport data session.
+
+Build:
+
+    $ make
+
+Run (as root):
+
+    # ./extract-handshakes.sh
+    New handshake session:
+      LOCAL_STATIC_PRIVATE_KEY = QChaGDXeH3eQsbFAhueUNWFdq9KfpF3yl+eITjZbXEk=
+      REMOTE_STATIC_PUBLIC_KEY = HzgTY6aWXtuSyW/PUquZtg8LB/DyMwEXGkPiEmdSsUU=
+      LOCAL_EPHEMERAL_PRIVATE_KEY = UNGdRHuKDeqbFvmiV5FD4wP7a8PqI6v3Xnnz6Jc6NXQ=
+      PRESHARED_KEY = AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=

contrib/extract-handshakes/extract-handshakes.sh

@@ -0,0 +1,80 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+# Copyright (C) 2017-2018 Peter Wu <peter@lekensteyn.nl>. All Rights Reserved.
+
+set -e
+
+ME_DIR="${BASH_SOURCE[0]}"
+ME_DIR="${ME_DIR%/*}"
+source "$ME_DIR/offsets.include" || { echo "Did you forget to run make?" >&2; exit 1; }
+
+case "$(uname -m)" in
+	x86_64) ARGUMENT_REGISTER="%si" ;;
+	i386|i686) ARGUMENT_REGISTER="%dx" ;;
+	aarch64) ARGUMENT_REGISTER="%x1" ;;
+	arm) ARGUMENT_REGISTER="%r1" ;;
+	*) echo "ERROR: Unknown architecture" >&2; exit 1 ;;
+esac
+
+ARGS=( )
+REGEX=".*: idxadd: .*"
+for key in "${!OFFSETS[@]}"; do
+	values="${OFFSETS[$key]}"
+	values=( ${values//,/ } )
+	for i in {0..3}; do
+		value="$ARGUMENT_REGISTER"
+		for indirection in "${values[@]:1}"; do
+			value="+$indirection($value)"
+		done
+		value="+$((i * 8 + values[0]))($value)"
+		ARGS+=( "${key,,}$i=$value:x64" )
+		REGEX="$REGEX ${key,,}$i=0x([0-9a-f]+)"
+	done
+done
+
+turn_off() {
+	set +e
+	[[ -f /sys/kernel/debug/tracing/events/wireguard/idxadd/enable ]] || exit
+	echo 0 > /sys/kernel/debug/tracing/events/wireguard/idxadd/enable
+	echo "-:wireguard/idxadd" >> /sys/kernel/debug/tracing/kprobe_events
+	exit
+}
+
+trap turn_off INT TERM EXIT
+echo "p:wireguard/idxadd index_hashtable_insert ${ARGS[*]}" >> /sys/kernel/debug/tracing/kprobe_events
+echo 1 > /sys/kernel/debug/tracing/events/wireguard/idxadd/enable
+
+unpack_u64() {
+	local i expanded="$1"
+	if [[ $ENDIAN == big ]]; then
+		printf -v expanded "%.*s$expanded" $((16 - ${#expanded})) 0000000000000000
+		for i in {0..7}; do
+			echo -n "\\x${expanded:(i * 2):2}"
+		done
+	elif [[ $ENDIAN == little ]]; then
+		(( ${#expanded} % 2 == 1 )) && expanded="0$expanded"
+		expanded="${expanded}0000000000000000"
+		for i in {0..7}; do
+			echo -n "\\x${expanded:((7 - i) * 2):2}"
+		done
+	else
+		echo "ERROR: Unable to determine endian" >&2
+		exit 1
+	fi
+}
+
+while read -r line; do
+	[[ $line =~ $REGEX ]] || continue
+	echo "New handshake session:"
+	j=1
+	for key in "${!OFFSETS[@]}"; do
+		bytes=""
+		for i in {0..3}; do
+			bytes="$bytes$(unpack_u64 "${BASH_REMATCH[j]}")"
+			((++j))
+		done
+		echo "  $key = $(printf "$bytes" | base64)"
+	done
+done < /sys/kernel/debug/tracing/trace_pipe

contrib/extract-handshakes/offset-finder.c

@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+struct def {
+	const char *name;
+	unsigned long offset;
+	unsigned long indirection_offset;
+};
+extern const struct def defs[];
+
+#ifdef __KERNEL__
+#include "../../../src/noise.h"
+
+const struct def defs[] = {
+	{ "LOCAL_STATIC_PRIVATE_KEY", offsetof(struct noise_static_identity, static_private), offsetof(struct noise_handshake, static_identity) },
+	{ "LOCAL_EPHEMERAL_PRIVATE_KEY", offsetof(struct noise_handshake, ephemeral_private), -1 },
+	{ "REMOTE_STATIC_PUBLIC_KEY", offsetof(struct noise_handshake, remote_static), -1 },
+	{ "PRESHARED_KEY", offsetof(struct noise_handshake, preshared_key), -1 },
+	{ NULL, 0 }
+};
+#else
+#include <stdio.h>
+int main(int argc, char *argv[])
+{
+	puts("declare -A OFFSETS=(");
+	for (const struct def *def = defs; def->name; ++def) {
+		printf("\t[%s]=%ld", def->name, def->offset);
+		if (def->indirection_offset != -1)
+			printf(",%ld", def->indirection_offset);
+		putchar('\n');
+	}
+	puts(")");
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	puts("ENDIAN=big");
+#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	puts("ENDIAN=little");
+#else
+#error "Unsupported endianness"
+#endif
+	return 0;
+}
+#endif