serene

Collection of scripts to automate VM creation for testing Linux kernel builds.

Workflow example

1. Create rootfs and host configurations

$ ./tools/create-rootfs.sh

2. Pull the Linux source code

$ git submodule update --init -- src/linux

3. Make default kernel config

$ ./tools/make-defconfig.sh

4. Build the Linux kernel

$ ./tools/build-kernel.sh

5. Start VM

$ ./tools/start-vm.sh

6. SSH into vm

$ ssh test

7. Stop VM

$ ./tools/stop-vm.sh

Arguments to the VM

Optional arguments to start-vm.sh:

-c: CPU security related parameters (smep, smap)
-k: Kernel security (kpti=1, kaslr)
-d: Launch in debug mode
-w: Wait for gdb to attach

Examples:

$ ./tools/start-vm.sh -c smep
$ ./tools/start-vm.sh -c smap
$ ./tools/start-vm.sh -c smep,smap
$ ./tools/start-vm.sh -k kpti=1
$ ./tools/start-vm.sh -k kaslr
$ ./tools/start-vm.sh -k kpti=1,kaslr
$ ./tools/start-vm.sh -c smep,smap -k kpti=1,kaslr

Debugging the Linux kernel

The vm is launched in debug mode as shown below. Note that the same serial line is used for both console and debugger, for which the debugger will take over and we will not be seing the Linux console messages.

[cpey@nuc dev]$ ./tools/start-vm.sh -d -w
QEMU 4.2.1 monitor - type 'help' for more information
(qemu)

and connect a gdb client:

[cpey@nuc linux]$ gdb -q vmlinux
Reading symbols from vmlinux...
(gdb) target remote :1234
Remote debugging using :1234
kgdb_breakpoint () at kernel/debug/debug_core.c:1196
1196            wmb(); /* Sync point after breakpoint */
(gdb)

Serene uses kgdb since Qemu gdb server does not take care of interrupts while debugging. Build the kernel with the following .config options:

CONFIG_KGDB=y
CONFIG_KGDB_SERIAL_CONSOLE=y

When the vm is launched without the -w flag, execute the following command from within the vm to enter kgdb before attaching the gdb client:

test@test:~$ sudo sh -c "echo g > /proc/sysrq-trigger"