Subject: [PATCH bpf-next 10/13] bpf: fix net.core.bpf_jit_enable race

From: Alexei Starovoitov <[email-masked]>
Date: Thu, 14 Dec 2017 17:55:14 -0800

From: Alexei Starovoitov <[email-masked]>

global bpf_jit_enable variable is tested multiple times in JITs,
blinding and verifier core. The malicious root can try to toggle
it while loading the programs. This race condition was accounted
for and there should be no issues, but it's safer to avoid
this race condition.

Signed-off-by: Alexei Starovoitov <[email-masked]>
Acked-by: Daniel Borkmann <[email-masked]>
---
 arch/arm/net/bpf_jit_32.c         | 2 +-
 arch/arm64/net/bpf_jit_comp.c     | 2 +-
 arch/mips/net/ebpf_jit.c          | 2 +-
 arch/powerpc/net/bpf_jit_comp64.c | 2 +-
 arch/s390/net/bpf_jit_comp.c      | 2 +-
 arch/sparc/net/bpf_jit_comp_64.c  | 2 +-
 arch/x86/net/bpf_jit_comp.c       | 2 +-
 include/linux/filter.h            | 5 +++--
 kernel/bpf/core.c                 | 3 ++-
 kernel/bpf/verifier.c             | 2 +-
 10 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index c199990e12b6..4425189bb24c 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -1824,7 +1824,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	/* If BPF JIT was not enabled then we must fall back to
 	 * the interpreter.
 	 */
-	if (!bpf_jit_enable)
+	if (!prog->jit_requested)
 		return orig_prog;
 
 	/* If constant blinding was enabled and we failed during blinding
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index ba38d403abb2..288137cb0871 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -844,7 +844,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	int image_size;
 	u8 *image_ptr;
 
-	if (!bpf_jit_enable)
+	if (!prog->jit_requested)
 		return orig_prog;
 
 	tmp = bpf_jit_blind_constants(prog);
diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 962b0259b4b6..97069a1b6f43 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -1869,7 +1869,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	unsigned int image_size;
 	u8 *image_ptr;
 
-	if (!bpf_jit_enable || !cpu_has_mips64r2)
+	if (!prog->jit_requested || !cpu_has_mips64r2)
 		return prog;
 
 	tmp = bpf_jit_blind_constants(prog);
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 46d74e81aff1..d5a5bc43cf8f 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -993,7 +993,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	struct bpf_prog *tmp_fp;
 	bool bpf_blinded = false;
 
-	if (!bpf_jit_enable)
+	if (!fp->jit_requested)
 		return org_fp;
 
 	tmp_fp = bpf_jit_blind_constants(org_fp);
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index e81c16838b90..f4baa8c514d3 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1300,7 +1300,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	struct bpf_jit jit;
 	int pass;
 
-	if (!bpf_jit_enable)
+	if (!fp->jit_requested)
 		return orig_fp;
 
 	tmp = bpf_jit_blind_constants(fp);
diff --git a/arch/sparc/net/bpf_jit_comp_64.c b/arch/sparc/net/bpf_jit_comp_64.c
index 5765e7e711f7..a2f1b5e774a7 100644
--- a/arch/sparc/net/bpf_jit_comp_64.c
+++ b/arch/sparc/net/bpf_jit_comp_64.c
@@ -1517,7 +1517,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	u8 *image_ptr;
 	int pass;
 
-	if (!bpf_jit_enable)
+	if (!prog->jit_requested)
 		return orig_prog;
 
 	tmp = bpf_jit_blind_constants(prog);
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 0554e8aef4d5..68859b58ab84 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1121,7 +1121,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	int pass;
 	int i;
 
-	if (!bpf_jit_enable)
+	if (!prog->jit_requested)
 		return orig_prog;
 
 	tmp = bpf_jit_blind_constants(prog);
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f26e6da1007b..3d6edc34932c 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -458,6 +458,7 @@ struct bpf_binary_header {
 struct bpf_prog {
 	u16			pages;		/* Number of allocated pages */
 	u16			jited:1,	/* Is our filter JIT'ed? */
+				jit_requested:1,/* archs need to JIT the prog */
 				locked:1,	/* Program image locked? */
 				gpl_compatible:1, /* Is filter GPL compatible? */
 				cb_access:1,	/* Is control block accessed? */
@@ -804,7 +805,7 @@ static inline bool bpf_prog_ebpf_jited(const struct bpf_prog *fp)
 	return fp->jited && bpf_jit_is_ebpf();
 }
 
-static inline bool bpf_jit_blinding_enabled(void)
+static inline bool bpf_jit_blinding_enabled(struct bpf_prog *prog)
 {
 	/* These are the prerequisites, should someone ever have the
 	 * idea to call blinding outside of them, we make sure to
@@ -812,7 +813,7 @@ static inline bool bpf_jit_blinding_enabled(void)
 	 */
 	if (!bpf_jit_is_ebpf())
 		return false;
-	if (!bpf_jit_enable)
+	if (!prog->jit_requested)
 		return false;
 	if (!bpf_jit_harden)
 		return false;
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index dc12c4fd006e..bda911644b1c 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -94,6 +94,7 @@ struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags)
 	fp->pages = size / PAGE_SIZE;
 	fp->aux = aux;
 	fp->aux->prog = fp;
+	fp->jit_requested = ebpf_jit_enabled();
 
 	INIT_LIST_HEAD_RCU(&fp->aux->ksym_lnode);
 
@@ -721,7 +722,7 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
 	struct bpf_insn *insn;
 	int i, rewritten;
 
-	if (!bpf_jit_blinding_enabled())
+	if (!bpf_jit_blinding_enabled(prog))
 		return prog;
 
 	clone = bpf_prog_clone_create(prog, GFP_USER);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cdc1f043c69b..8e0e4cd0d5e4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5080,7 +5080,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
 		/* BPF_EMIT_CALL() assumptions in some of the map_gen_lookup
 		 * handlers are currently limited to 64 bit only.
 		 */
-		if (ebpf_jit_enabled() && BITS_PER_LONG == 64 &&
+		if (prog->jit_requested && BITS_PER_LONG == 64 &&
 		    insn->imm == BPF_FUNC_map_lookup_elem) {
 			map_ptr = env->insn_aux_data[i + delta].map_ptr;
 			if (map_ptr == BPF_MAP_PTR_POISON ||
-- 
2.9.5