bpf: get rid of pure_initcall dependency to enable jits

commit fa9dd599b4dae841924b022768354cfde9affecb upstream.

Having a pure_initcall() callback just to permanently enable BPF
JITs under CONFIG_BPF_JIT_ALWAYS_ON is unnecessary and could leave
a small race window in future where JIT is still disabled on boot.
Since we know about the setting at compilation time anyway, just
initialize it properly there. Also consolidate all the individual
bpf_jit_enable variables into a single one and move them under one
location. Moreover, don't allow for setting unspecified garbage
values on them.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[bwh: Backported to 4.9 as dependency of commit 2e4a30983b0f
 "bpf: restrict access to core bpf sysctls":
 - Drop change in arch/mips/net/ebpf_jit.c
 - Drop change to bpf_jit_kallsyms
 - Adjust filenames, context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chatur27 <jasonbright2709@gmail.com>

10 files changed, 20 insertions, 32 deletions

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 93d0b6d0b63e..7fd448b23b94 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -72,8 +72,6 @@ struct jit_ctx {
 #endif
 };
 
-int bpf_jit_enable __read_mostly;
-
 static inline int call_neg_helper(struct sk_buff *skb, int offset, void *ret,
 		      unsigned int size)
 {
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index cdeb270ad979..0713867d0117 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -30,8 +30,6 @@
 
 #include "bpf_jit.h"
 
-int bpf_jit_enable __read_mostly;
-
 #define TMP_REG_1 (MAX_BPF_JIT_REG + 0)
 #define TMP_REG_2 (MAX_BPF_JIT_REG + 1)
 #define TCALL_CNT (MAX_BPF_JIT_REG + 2)
diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 742daf8351b9..08bf4f56c3b4 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c
@@ -1195,8 +1195,6 @@ jmp_cmp:
 	return 0;
 }
 
-int bpf_jit_enable __read_mostly;
-
 void bpf_jit_compile(struct bpf_prog *fp)
 {
 	struct jit_ctx ctx;
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 345e255c06a2..9cbc64a8f15a 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -18,8 +18,6 @@
 
 #include "bpf_jit.h"
 
-int bpf_jit_enable __read_mostly;
-
 static inline void bpf_flush_icache(void *start, void *end)
 {
 	smp_wmb();
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 62edec9695e6..633172c5b065 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -28,8 +28,6 @@
 #include <asm/nospec-branch.h>
 #include "bpf_jit.h"
 
-int bpf_jit_enable __read_mostly;
-
 struct bpf_jit {
 	u32 seen;		/* Flags to remember seen eBPF instructions */
 	u32 seen_reg[16];	/* Array to remember which registers are used */
diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
index 3e6e05a7c4c2..5db3a27bcb94 100644
--- a/arch/sparc/net/bpf_jit_comp.c
+++ b/arch/sparc/net/bpf_jit_comp.c
@@ -10,8 +10,6 @@
 
 #include "bpf_jit.h"
 
-int bpf_jit_enable __read_mostly;
-
 static inline bool is_simm13(unsigned int value)
 {
 	return value + 0x1000 < 0x2000;
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index c36764361d61..85a7c0b0627c 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -15,8 +15,6 @@
 #include <asm/nospec-branch.h>
 #include <linux/bpf.h>
 
-int bpf_jit_enable __read_mostly;
-
 /*
  * assembly code in arch/x86/net/bpf_jit.S
  */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 66d64db4f8c7..64ccb4fbf15b 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -208,6 +208,10 @@ 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);
+int bpf_jit_harden   __read_mostly;
+
 struct bpf_binary_header *
 bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
 		     unsigned int alignment,
@@ -244,8 +248,6 @@ void bpf_jit_binary_free(struct bpf_binary_header *hdr)
 	module_memfree(hdr);
 }
 
-int bpf_jit_harden __read_mostly;
-
 static int bpf_jit_blind_insn(const struct bpf_insn *from,
 			      const struct bpf_insn *aux,
 			      struct bpf_insn *to_buff)
@@ -925,8 +927,13 @@ load_byte:
 STACK_FRAME_NON_STANDARD(__bpf_prog_run); /* jump table */
 
 #else
-static unsigned int __bpf_prog_ret0(void *ctx, const struct bpf_insn *insn)
+static unsigned int __bpf_prog_ret0_warn(void *ctx,
+					 const struct bpf_insn *insn)
 {
+	/* If this handler ever gets executed, then BPF_JIT_ALWAYS_ON
+	 * is not working properly, so warn about it!
+	 */
+	WARN_ON_ONCE(1);
 	return 0;
 }
 #endif
@@ -981,7 +988,7 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
 	fp->bpf_func = (void *) __bpf_prog_run;
 #else
-	fp->bpf_func = (void *) __bpf_prog_ret0;
+	fp->bpf_func = (void *) __bpf_prog_ret0_warn;
 #endif
 
 	/* eBPF JITs can rewrite the program in case constant
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 546ba76b35a5..7b7d26a4f8c8 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -24,6 +24,7 @@
 
 static int zero = 0;
 static int one = 1;
+static int two __maybe_unused = 2;
 static int min_sndbuf = SOCK_MIN_SNDBUF;
 static int min_rcvbuf = SOCK_MIN_RCVBUF;
 static int max_skb_frags = MAX_SKB_FRAGS;
@@ -292,13 +293,14 @@ static struct ctl_table net_core_table[] = {
 		.data		= &bpf_jit_enable,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-#ifndef CONFIG_BPF_JIT_ALWAYS_ON
-		.proc_handler	= proc_dointvec
-#else
 		.proc_handler	= proc_dointvec_minmax,
+# ifdef CONFIG_BPF_JIT_ALWAYS_ON
 		.extra1		= &one,
 		.extra2		= &one,
-#endif
+# else
+		.extra1		= &zero,
+		.extra2		= &two,
+# endif
 	},
 # ifdef CONFIG_HAVE_EBPF_JIT
 	{
@@ -306,7 +308,9 @@ static struct ctl_table net_core_table[] = {
 		.data		= &bpf_jit_harden,
 		.maxlen		= sizeof(int),
 		.mode		= 0600,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &two,
 	},
 # endif
 #endif
diff --git a/net/socket.c b/net/socket.c
index d802296b9c46..07b1143d03dd 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2597,15 +2597,6 @@ out_fs:
 
 core_initcall(sock_init);	/* early initcall */
 
-static int __init jit_init(void)
-{
-#ifdef CONFIG_BPF_JIT_ALWAYS_ON
-	bpf_jit_enable = 1;
-#endif
-	return 0;
-}
-pure_initcall(jit_init);
-
 #ifdef CONFIG_PROC_FS
 void socket_seq_show(struct seq_file *seq)
 {