Kernel live patching

Kernel Live Patching (KLP) enables the capacity to apply patch to the kernel without rebooting the system.

To use KLP, you should follow the following steps:

• Run a livepatching enabled kernel
• Obtain the source tree of the kernel
• Prepare and build the patch
• Apply the patch

You can use Kernel Live Patching in Alpine Linux by running a modified kernel.

Building the kernel

1. Obtain the source
2. Enable the following flag CONFIG_LIVEPATCH and CONFIG_DEBUG_INFO
3. Build the kernel: make
4. Install: doas make modules_install && doas make install
5. Rebuild initramfs
6. Update bootloader
7. Reboot: doas reboot

Patching the kernel

1. Install kpatch: doas apk add kpatch
2. Prepare the patch. You can create a file some.patch containing something around the following (it can need update depending on the kernel version):

Index: src/fs/proc/meminfo.c
===================================================================
--- src.orig/fs/proc/meminfo.c
+++ src/fs/proc/meminfo.c
@@ -95,7 +95,7 @@ static int meminfo_proc_show(struct seq_
 		"Committed_AS:   %8lu kB\n"
 		"VmallocTotal:   %8lu kB\n"
 		"VmallocUsed:    %8lu kB\n"
-		"VmallocChunk:   %8lu kB\n"
+		"VMALLOCCHUNK:   %8lu kB\n"
 #ifdef CONFIG_MEMORY_FAILURE
 		"HardwareCorrupted: %5lu kB\n"
 #endif

1. Build the patch: kpatch-build -s /path/to/kernel/source some.patch

Enabling the patch

1. Enable the patch: doas insmod kpatch-some.ko or doas kpatch load kpatch-some.ko
2. Check that the patch has been loaded: grep -i chunk /proc/meminfo
3. Disable the patch: doas kpatch unload kpatch-some.ko