kheaders: Move from proc to sysfs

The kheaders archive consisting of the kernel headers used for compiling
bpf programs is in /proc. However there is concern that moving it here
will make it permanent. Let us move it to /sys/kernel as discussed [1].

[1] https://lore.kernel.org/patchwork/patch/1067310/#1265969

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

init/Kconfig

@@ -579,15 +579,14 @@ config IKCONFIG_PROC
 	  This option enables access to the kernel configuration file
 	  through /proc/config.gz.
 
-config IKHEADERS_PROC
-	tristate "Enable kernel header artifacts through /proc/kheaders.tar.xz"
-	depends on PROC_FS
+config IKHEADERS
+	tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
+	depends on SYSFS
 	help
-	  This option enables access to the kernel header and other artifacts that
-	  are generated during the build process. These can be used to build eBPF
-	  tracing programs, or similar programs.  If you build the headers as a
-	  module, a module called kheaders.ko is built which can be loaded on-demand
-	  to get access to the headers.
+	  This option enables access to the in-kernel headers that are generated during
+	  the build process. These can be used to build eBPF tracing programs,
+	  or similar programs.  If you build the headers as a module, a module called
+	  kheaders.ko is built which can be loaded on-demand to get access to headers.
 
 config LOG_BUF_SHIFT
 	int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"

kernel/Makefile

@@ -71,7 +71,7 @@ obj-$(CONFIG_UTS_NS) += utsname.o
 obj-$(CONFIG_USER_NS) += user_namespace.o
 obj-$(CONFIG_PID_NS) += pid_namespace.o
 obj-$(CONFIG_IKCONFIG) += configs.o
-obj-$(CONFIG_IKHEADERS_PROC) += kheaders.o
+obj-$(CONFIG_IKHEADERS) += kheaders.o
 obj-$(CONFIG_SMP) += stop_machine.o
 obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o
@@ -127,7 +127,7 @@ $(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
 $(obj)/kheaders.o: $(obj)/kheaders_data.tar.xz
 
 quiet_cmd_genikh = CHK     $(obj)/kheaders_data.tar.xz
-cmd_genikh = $(CONFIG_SHELL) $(srctree)/kernel/gen_ikh_data.sh $@
+cmd_genikh = $(CONFIG_SHELL) $(srctree)/kernel/gen_kheaders.sh $@
 $(obj)/kheaders_data.tar.xz: FORCE
 	$(call cmd,genikh)
 

kernel/gen_kheaders.sh

@@ -2,7 +2,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 # This script generates an archive consisting of kernel headers
-# for CONFIG_IKHEADERS_PROC.
+# for CONFIG_IKHEADERS.
 set -e
 spath="$(dirname "$(readlink -f "$0")")"
 kroot="$spath/.."

kernel/kheaders.c

@@ -8,9 +8,8 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/proc_fs.h>
+#include <linux/kobject.h>
 #include <linux/init.h>
-#include <linux/uaccess.h>
 
 /*
  * Define kernel_headers_data and kernel_headers_data_end, within which the
@@ -31,39 +30,32 @@ extern char kernel_headers_data;
 extern char kernel_headers_data_end;
 
 static ssize_t
-ikheaders_read_current(struct file *file, char __user *buf,
-		      size_t len, loff_t *offset)
+ikheaders_read(struct file *file,  struct kobject *kobj,
+	       struct bin_attribute *bin_attr,
+	       char *buf, loff_t off, size_t len)
 {
-	return simple_read_from_buffer(buf, len, offset,
-				       &kernel_headers_data,
-				       &kernel_headers_data_end -
-				       &kernel_headers_data);
+	memcpy(buf, &kernel_headers_data + off, len);
+	return len;
 }
 
-static const struct file_operations ikheaders_file_ops = {
-	.read = ikheaders_read_current,
-	.llseek = default_llseek,
+static struct bin_attribute kheaders_attr __ro_after_init = {
+	.attr = {
+		.name = "kheaders.tar.xz",
+		.mode = 0444,
+	},
+	.read = &ikheaders_read,
 };
 
 static int __init ikheaders_init(void)
 {
-	struct proc_dir_entry *entry;
-
-	/* create the current headers file */
-	entry = proc_create("kheaders.tar.xz", S_IRUGO, NULL,
-			    &ikheaders_file_ops);
-	if (!entry)
-		return -ENOMEM;
-
-	proc_set_size(entry,
-		      &kernel_headers_data_end -
-		      &kernel_headers_data);
-	return 0;
+	kheaders_attr.size = (&kernel_headers_data_end -
+			      &kernel_headers_data);
+	return sysfs_create_bin_file(kernel_kobj, &kheaders_attr);
 }
 
 static void __exit ikheaders_cleanup(void)
 {
-	remove_proc_entry("kheaders.tar.xz", NULL);
+	sysfs_remove_bin_file(kernel_kobj, &kheaders_attr);
 }
 
 module_init(ikheaders_init);