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bpf: add ability to configure BPF JIT kallsyms export at the boot time

PATCH In review Eugene Syromiatnikov 2 participants 2 messages May 23, 2018 – Jun 10, 2018

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Networking Network drivers Documentation BPF +1 more subsystems
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Eugene Syromiatnikov

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#0 lore raw

PATCH 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 <[email protected]>
---
 Documentation/admin-guide/kernel-parameters.txt | 10 +++++++++
 init/Kconfig                                    | 30 +++++++++++++++++++++++++
 kernel/bpf/core.c                               | 14 ++++++++++++
 3 files changed, 54 insertions(+)
Documentation/admin-guide/kernel-parameters.txt +10 -0
index 5adc6d0..10e7502 100644
@@ -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.
init/Kconfig +30 -0
index b661497..b5405ca 100644
@@ -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
kernel/bpf/core.c +14 -0
index 9edb7a8..003d708 100644
@@ -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,
Signature · 1 line
2.1.4
build bot
#1 lore raw
Thank you for the patch! Yet something to improve:

Hi Eugene,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Eugene-Syromiatnikov/bpf-add-boot-parameters-for-sysctl-knobs/20180526-164048
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: i386-randconfig-x074-06101602 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386

All errors (new ones prefixed by >>):

>> kernel//bpf/core.c:325:38: error: 'CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM_VALUE' undeclared here (not in a function); did you mean 'CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM'?
    int bpf_jit_kallsyms __read_mostly = CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM_VALUE;
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                         CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM

vim +325 kernel//bpf/core.c

323
324 #ifdef CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM

 > 325	int bpf_jit_kallsyms __read_mostly = CONFIG_BPF_JIT_KALLSYMS_BOOTPARAM_VALUE;

326

---
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https://lists.01.org/pipermail/kbuild-all Intel Corporation