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Subject[PATCH bpf-next v2 3/3] bpf: add ability to configure BPF JIT kallsyms export at the boot time
This patch introduces two configuration options,
BPF_JIT_KALLSYMS_BOOTPARAM and BPF_JIT_KALLSYMS_BOOTPARAM_VALUE, that
allow configuring the initial value of net.core.bpf_jit_kallsyms sysctl
knob. This enables export of addresses of JIT'ed BPF programs that
created during the early boot.

Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
Documentation/admin-guide/kernel-parameters.txt | 10 +++++++++
init/Kconfig | 30 +++++++++++++++++++++++++
kernel/bpf/core.c | 14 ++++++++++++
3 files changed, 54 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5adc6d0..10e7502 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -452,6 +452,16 @@
2 - JIT hardening is enabled for all users.
Default value is set via kernel config option.

+ bpf_jit_kallsyms=
+ Format: { "0" | "1" }
+ Sets initial value of net.core.bpf_jit_kallsyms
+ sysctl knob.
+ 0 - Addresses of JIT'ed BPF programs are not exported
+ to kallsyms.
+ 1 - Export of addresses of JIT'ed BPF programs is
+ enabled for privileged 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 b661497..b5405ca 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1464,6 +1464,36 @@ config BPF_JIT_HARDEN_BOOTPARAM_VALUE

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

+config BPF_JIT_KALLSYMS_BOOTPARAM
+ bool "BPF JIT kallsyms export boot parameter"
+ default n
+ help
+ This option adds a kernel parameter 'bpf_jit_kallsyms' that allows
+ configuring default state of the net.core.bpf_jit_kallsyms sysctl
+ knob. If this option is selected, the default value of the
+ net.core.bpf_jit_kallsyms sysctl knob can be set on the kernel command
+ line. The purpose of this option is to allow enabling BPF JIT
+ kallsyms export for the BPF programs created during the early boot,
+ so they can be traced later.
+
+ If you are unsure how to answer this question, answer N.
+
+config BPF_JIT_KALLSYMS_BOOTPARAM_VALUE
+ int "BPF JIT kallsyms export boot parameter default value"
+ depends on BPF_JIT_HARDEN_BOOTPARAM
+ range 0 1
+ default 0
+ help
+ This option sets the default value for the kernel parameter
+ 'bpf_jit_kallsyms' that configures default value of the
+ net.core.bpf_jit_kallsyms sysctl knob at boot. If this option is set
+ to 0 (zero), the net.core.bpf_jit_kallsyms will default to 0, which
+ will lead to disabling of exporting of addresses of JIT'ed BPF
+ programs. If this option is set to 1 (one), addresses of privileged
+ BPF programs are exported to kallsyms.
+
+ 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 9edb7a8..003d708 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -321,7 +321,21 @@ __setup("bpf_jit_harden=", bpf_jit_harden_setup);
int bpf_jit_harden __read_mostly;
#endif /* CONFIG_BPF_JIT_HARDEN_BOOTPARAM */

+#ifdef CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM
+int bpf_jit_kallsyms __read_mostly = CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM_VALUE;
+
+static int __init bpf_jit_kallsyms_setup(char *str)
+{
+ unsigned long enabled;
+
+ if (!kstrtoul(str, 0, &enabled))
+ bpf_jit_kallsyms = !!enabled;
+ return 1;
+}
+__setup("bpf_jit_kallsyms=", bpf_jit_kallsyms_setup);
+#else /* !CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM */
int bpf_jit_kallsyms __read_mostly;
+#endif /* CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM */

static __always_inline void
bpf_get_prog_addr_region(const struct bpf_prog *prog,
--
2.1.4
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