bpf: get rid of pure_initcall dependency to enable jits

commit fa9dd599 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 2e4a3098
 "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>

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)
 {

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)

arch/mips/net/bpf_jit.c

@@ -1194,8 +1194,6 @@ static int build_body(struct jit_ctx *ctx)
 	return 0;
 }
 
-int bpf_jit_enable __read_mostly;
-
 void bpf_jit_compile(struct bpf_prog *fp)
 {
 	struct jit_ctx ctx;

arch/powerpc/net/bpf_jit_comp.c

@@ -18,8 +18,6 @@
 
 #include "bpf_jit32.h"
 
-int bpf_jit_enable __read_mostly;
-
 static inline void bpf_flush_icache(void *start, void *end)
 {
 	smp_wmb();

arch/powerpc/net/bpf_jit_comp64.c

@@ -21,8 +21,6 @@
 
 #include "bpf_jit64.h"
 
-int bpf_jit_enable __read_mostly;
-
 static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
 {
 	int *p = area;

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 */

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;

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
  */

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 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 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

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

net/socket.c

@@ -2550,15 +2550,6 @@ static int __init sock_init(void)
 
 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)
 {