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Subject[PATCH bpf-next v2 2/3] bpf: add ability to configure BPF JIT hardening via boot-time parameter
This patch introduces two configuration options,
BPF_JIT_HARDEN_BOOTPARAM and BPF_JIT_HARDEN_BOOTPARAM_VALUE, that allow
configuring the initial value of net.core.bpf_jit_harden sysctl knob,
which is useful for enforcing JIT hardening during the early boot.

Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
Documentation/admin-guide/kernel-parameters.txt | 10 +++++++++
init/Kconfig | 29 +++++++++++++++++++++++++
kernel/bpf/core.c | 17 +++++++++++++++
3 files changed, 56 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index aa8e831..5adc6d0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -442,6 +442,16 @@
bert_disable [ACPI]
Disable BERT OS support on buggy BIOSes.

+ bpf_jit_harden=
+ Format: { "0" | "1" | "2" }
+ Sets initial value of net.core.bpf_jit_harden
+ sysctl knob.
+ 0 - JIT hardening is disabled.
+ 1 - JIT hardening is enabled for unprivileged users
+ only.
+ 2 - JIT hardening is enabled for all users.
+ Default value is set via kernel config option.
+
bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
bttv.radio= Most important insmod options are available as
kernel args too.
diff --git a/init/Kconfig b/init/Kconfig
index 1403a3e..b661497 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1435,6 +1435,35 @@ config UNPRIVILEGED_BPF_BOOTPARAM_VALUE

If you are unsure how to answer this question, answer 0.

+config BPF_JIT_HARDEN_BOOTPARAM
+ bool "BPF JIT harden boot parameter"
+ default n
+ help
+ This option adds a kernel parameter 'bpf_jit_harden' that allows
+ configuring default state of the net.core.bpf_jit_harden sysctl knob.
+ If this option is selected, the default value of the
+ net.core.bpf_jit_harden sysctl knob can be set on the kernel command
+ line. The purpose of this option is to allow enabling BPF JIT
+ hardening for the BPF programs created during the early boot.
+
+ If you are unsure how to answer this question, answer N.
+
+config BPF_JIT_HARDEN_BOOTPARAM_VALUE
+ int "BPF JIT harden boot parameter default value"
+ depends on BPF_JIT_HARDEN_BOOTPARAM
+ range 0 2
+ default 0
+ help
+ This option sets the default value for the kernel parameter
+ 'bpf_jit_enabled' that configures default value of the
+ net.core.bpf_jit_harden sysctl knob at boot. If this option is set to
+ 0 (zero), the net.core.bpf_jit_harden will default to 0, which will
+ lead to no hardening at bootup. If this option is set to 1 (one),
+ hardening will be applied only to unprivileged users only. If this
+ option is set to 2 (two), JIT hardening will be enabled for all users.
+
+ 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/core.c b/kernel/bpf/core.c
index 2194c6a..9edb7a8 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -32,6 +32,7 @@
#include <linux/kallsyms.h>
#include <linux/rcupdate.h>
#include <linux/perf_event.h>
+#include <linux/init.h>

#include <asm/unaligned.h>

@@ -303,7 +304,23 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
#ifdef CONFIG_BPF_JIT
/* All BPF JIT sysctl knobs here. */
int bpf_jit_enable __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_ALWAYS_ON);
+
+#ifdef CONFIG_BPF_JIT_HARDEN_BOOTPARAM
+int bpf_jit_harden __read_mostly = CONFIG_BPF_JIT_HARDEN_BOOTPARAM_VALUE;
+
+static int __init bpf_jit_harden_setup(char *str)
+{
+ unsigned long value;
+
+ if (!kstrtoul(str, 0, &value))
+ bpf_jit_harden = min(value, 2UL);
+ return 1;
+}
+__setup("bpf_jit_harden=", bpf_jit_harden_setup);
+#else /* !CONFIG_BPF_JIT_HARDEN_BOOTPARAM */
int bpf_jit_harden __read_mostly;
+#endif /* CONFIG_BPF_JIT_HARDEN_BOOTPARAM */
+
int bpf_jit_kallsyms __read_mostly;

static __always_inline void
--
2.1.4
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