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Subject[PATCH 1/3] bpf: add ability to configure unprivileged BPF via boot-time parameter
This patch introduces two configuration options,
UNPRIVILEGED_BPF_BOOTPARAM and UNPRIVILEGED_BPF_BOOTPARAM_VALUE, that
allow configuring the initial value of kernel.unprivileged_bpf_disabled
sysctl knob, which is useful for the cases when disabling unprivileged
bpf() access during the early boot is desirable.

Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
Documentation/admin-guide/kernel-parameters.txt | 8 +++++++
init/Kconfig | 31 +++++++++++++++++++++++++
kernel/bpf/syscall.c | 16 +++++++++++++
3 files changed, 55 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 11fc28e..aa8e831 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4355,6 +4355,14 @@
unknown_nmi_panic
[X86] Cause panic on unknown NMI.

+ unprivileged_bpf_disabled=
+ Format: { "0" | "1" }
+ Sets initial value of kernel.unprivileged_bpf_disabled
+ sysctl knob.
+ 0 - unprivileged bpf() syscall access enabled.
+ 1 - unprivileged bpf() syscall access disabled.
+ Default value is set via kernel config option.
+
usbcore.authorized_default=
[USB] Default USB device authorization:
(default -1 = authorized except for wireless USB,
diff --git a/init/Kconfig b/init/Kconfig
index 480a4f2..1403a3e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1404,6 +1404,37 @@ config BPF_JIT_ALWAYS_ON
Enables BPF JIT and removes BPF interpreter to avoid
speculative execution of BPF instructions by the interpreter

+config UNPRIVILEGED_BPF_BOOTPARAM
+ bool "Unprivileged bpf() boot parameter"
+ depends on BPF_SYSCALL
+ default n
+ help
+ This option adds a kernel parameter 'unprivileged_bpf_disabled'
+ that allows configuring default state of the
+ kernel.unprivileged_bpf_disabled sysctl knob.
+ If this option is selected, unprivileged access to the bpf() syscall
+ can be disabled with unprivileged_bpf_disabled=1 on the kernel command
+ line. The purpose of this option is to allow disabling unprivileged
+ bpf() syscall access during the early boot.
+
+ If you are unsure how to answer this question, answer N.
+
+config UNPRIVILEGED_BPF_BOOTPARAM_VALUE
+ int "Unprivileged bpf() boot parameter default value"
+ depends on UNPRIVILEGED_BPF_BOOTPARAM
+ range 0 1
+ default 0
+ help
+ This option sets the default value for the kernel parameter
+ 'unprivileged_bpf_disabled', which allows disabling unprivileged bpf()
+ syscall access at boot. If this option is set to 0 (zero), the
+ unprivileged bpf() boot kernel parameter will default to 0, allowing
+ unprivileged bpf() syscall access at bootup. If this option is
+ set to 1 (one), the unprivileged bpf() kernel parameter will default
+ to 1, disabling unprivileged bpf() syscall access at bootup.
+
+ If you are unsure how to answer this question, answer 0.
+
config USERFAULTFD
bool "Enable userfaultfd() system call"
select ANON_INODES
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index bfcde94..fdc5fd9 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -29,6 +29,7 @@
#include <linux/ctype.h>
#include <linux/btf.h>
#include <linux/nospec.h>
+#include <linux/init.h>

#define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PROG_ARRAY || \
(map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
@@ -45,7 +46,22 @@ static DEFINE_SPINLOCK(prog_idr_lock);
static DEFINE_IDR(map_idr);
static DEFINE_SPINLOCK(map_idr_lock);

+#ifdef CONFIG_UNPRIVILEGED_BPF_BOOTPARAM
+int sysctl_unprivileged_bpf_disabled __read_mostly =
+ CONFIG_UNPRIVILEGED_BPF_BOOTPARAM_VALUE;
+
+static int __init unprivileged_bpf_setup(char *str)
+{
+ unsigned long disabled;
+
+ if (!kstrtoul(str, 0, &disabled))
+ sysctl_unprivileged_bpf_disabled = !!disabled;
+ return 1;
+}
+__setup("unprivileged_bpf_disabled=", unprivileged_bpf_setup);
+#else /* !CONFIG_UNPRIVILEGED_BPF_BOOTPARAM */
int sysctl_unprivileged_bpf_disabled __read_mostly;
+#endif /* CONFIG_UNPRIVILEGED_BPF_BOOTPARAM */

static const struct bpf_map_ops * const bpf_map_types[] = {
#define BPF_PROG_TYPE(_id, _ops)
--
2.1.4
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