Compatibility with kernels >= 5.7

.gitignore

@@ -0,0 +1,9 @@
+*.ko
+*.mod
+*.mod.c
+*.o
+*.order
+*.symvers
+*.swp
+.*.cmd
+.tmp_versions

ashmem/deps.c

@@ -1,11 +1,69 @@
 #include <linux/mm.h>
 #include <linux/kallsyms.h>
+#include <linux/kprobes.h>
+#include <linux/version.h>
+
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
+
+#ifndef CONFIG_KPROBES
+# error "Your kernel does not support KProbes, but this is required to compile ashmem as a kernel module on kernel 5.7 and later"
+#endif
+
+typedef unsigned long (*kallsyms_lookup_name_t)(const char *name);
+
+static int dummy_kprobe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	return 0;
+}
+
+static kallsyms_lookup_name_t get_kallsyms_lookup_name_ptr(void)
+{
+	struct kprobe probe;
+	int ret;
+	kallsyms_lookup_name_t addr;
+
+	memset(&probe, 0, sizeof(probe));
+	probe.pre_handler = dummy_kprobe_handler;
+	probe.symbol_name = "kallsyms_lookup_name";
+	ret = register_kprobe(&probe);
+	if (ret)
+		return NULL;
+	addr = (kallsyms_lookup_name_t) probe.addr;
+	unregister_kprobe(&probe);
+
+	return addr;
+}
+#endif
+
+/*
+ * On kernel 5.7 and later, kallsyms_lookup_name() can no longer be called from a kernel
+ * module for reasons described here: https://lwn.net/Articles/813350/
+ * As ashmem really needs to use kallsysms_lookup_name() to access some kernel
+ * functions that otherwise wouldn't be accessible, KProbes are used on later
+ * kernels to get the address of kallsysms_lookup_name(). The function is
+ * afterwards used just as before. This is a very dirty hack though and the much
+ * better solution would be if all the functions that are currently resolved
+ * with kallsysms_lookup_name() would get an EXPORT_SYMBOL() annotation to
+ * make them directly accessible to kernel modules.
+ */
+static unsigned long kallsyms_lookup_name_wrapper(const char *name)
+{
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
+	static kallsyms_lookup_name_t func_ptr = NULL;
+	if (!func_ptr)
+		func_ptr = get_kallsyms_lookup_name_ptr();
+
+	return func_ptr(name);
+#else
+	return kallsyms_lookup_name(name);
+#endif
+}
 
 static int (*shmem_zero_setup_ptr)(struct vm_area_struct *) = NULL;
 
 int shmem_zero_setup(struct vm_area_struct *vma)
 {
 	if (!shmem_zero_setup_ptr)
-		shmem_zero_setup_ptr = kallsyms_lookup_name("shmem_zero_setup");
+		shmem_zero_setup_ptr = kallsyms_lookup_name_wrapper("shmem_zero_setup");
 	return shmem_zero_setup_ptr(vma);
 }

binder/Makefile

@@ -1,6 +1,6 @@
-ccflags-y += -I$(src) -Wno-int-conversion -DCONFIG_ANDROID_BINDER_DEVICES="\"binder\""
+ccflags-y += -I$(src) -Wno-int-conversion -DCONFIG_ANDROID_BINDER_DEVICES="\"binder\"" -DCONFIG_ANDROID_BINDERFS="y"
 obj-m := binder_linux.o
-binder_linux-y := deps.o binder.o
+binder_linux-y := deps.o binder.o binder_alloc.o binderfs.o
 
 KERNEL_SRC ?= /lib/modules/$(shell uname -r)/build
 
@@ -11,4 +11,4 @@ install:
 	cp binder_linux.ko $(DESTDIR)/
 
 clean:
-	rm -rf deps.h *.o *.ko *.mod.c *.symvers *.order .*.cmd .tmp_versions
+	rm -rf *.o *.ko *.mod.c *.symvers *.order .*.cmd .tmp_versions