CVE-2019-7308

@@ -172,6 +172,7 @@ struct bpf_verifier_state_list {
 #define BPF_ALU_SANITIZE_SRC		1U
 #define BPF_ALU_SANITIZE_DST		2U
 #define BPF_ALU_NEG_VALUE		(1U << 2)
+#define BPF_ALU_NON_POINTER		(1U << 3)
 #define BPF_ALU_SANITIZE		(BPF_ALU_SANITIZE_SRC | \
 					 BPF_ALU_SANITIZE_DST)
 

@@ -3103,6 +3103,40 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
 	}
 }
 
+static bool can_skip_alu_sanitation(const struct bpf_verifier_env *env,
+				    const struct bpf_insn *insn)
+{
+	return env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K;
+}
+
+static int update_alu_sanitation_state(struct bpf_insn_aux_data *aux,
+				       u32 alu_state, u32 alu_limit)
+{
+	/* If we arrived here from different branches with different
+	 * state or limits to sanitize, then this won't work.
+	 */
+	if (aux->alu_state &&
+	    (aux->alu_state != alu_state ||
+	     aux->alu_limit != alu_limit))
+		return -EACCES;
+
+	/* Corresponding fixup done in fixup_bpf_calls(). */
+	aux->alu_state = alu_state;
+	aux->alu_limit = alu_limit;
+	return 0;
+}
+
+static int sanitize_val_alu(struct bpf_verifier_env *env,
+			    struct bpf_insn *insn)
+{
+	struct bpf_insn_aux_data *aux = cur_aux(env);
+
+	if (can_skip_alu_sanitation(env, insn))
+		return 0;
+
+	return update_alu_sanitation_state(aux, BPF_ALU_NON_POINTER, 0);
+}
+
 static int sanitize_ptr_alu(struct bpf_verifier_env *env,
 			    struct bpf_insn *insn,
 			    const struct bpf_reg_state *ptr_reg,
@@ -3117,7 +3151,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
 	struct bpf_reg_state tmp;
 	bool ret;
 
-	if (env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K)
+	if (can_skip_alu_sanitation(env, insn))
 		return 0;
 
 	/* We already marked aux for masking from non-speculative
@@ -3133,19 +3167,8 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
 
 	if (retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg))
 		return 0;
-
-	/* If we arrived here from different branches with different
-	 * limits to sanitize, then this won't work.
-	 */
-	if (aux->alu_state &&
-	    (aux->alu_state != alu_state ||
-	     aux->alu_limit != alu_limit))
+	if (update_alu_sanitation_state(aux, alu_state, alu_limit))
 		return -EACCES;
-
-	/* Corresponding fixup done in fixup_bpf_calls(). */
-	aux->alu_state = alu_state;
-	aux->alu_limit = alu_limit;
-
 do_sim:
 	/* Simulate and find potential out-of-bounds access under
 	 * speculative execution from truncation as a result of
@@ -3418,6 +3441,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 	s64 smin_val, smax_val;
 	u64 umin_val, umax_val;
 	u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
+	u32 dst = insn->dst_reg;
+	int ret;
 
 	if (insn_bitness == 32) {
 		/* Relevant for 32-bit RSH: Information can propagate towards
@@ -3452,6 +3477,11 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 
 	switch (opcode) {
 	case BPF_ADD:
+		ret = sanitize_val_alu(env, insn);
+		if (ret < 0) {
+			verbose(env, "R%d tried to add from different pointers or scalars\n", dst);
+			return ret;
+		}
 		if (signed_add_overflows(dst_reg->smin_value, smin_val) ||
 		    signed_add_overflows(dst_reg->smax_value, smax_val)) {
 			dst_reg->smin_value = S64_MIN;
@@ -3471,6 +3501,11 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 		dst_reg->var_off = tnum_add(dst_reg->var_off, src_reg.var_off);
 		break;
 	case BPF_SUB:
+		ret = sanitize_val_alu(env, insn);
+		if (ret < 0) {
+			verbose(env, "R%d tried to sub from different pointers or scalars\n", dst);
+			return ret;
+		}
 		if (signed_sub_overflows(dst_reg->smin_value, smax_val) ||
 		    signed_sub_overflows(dst_reg->smax_value, smin_val)) {
 			/* Overflow possible, we know nothing */

@@ -148,6 +148,7 @@ struct bpf_verifier_state {
 	/* call stack tracking */
 	struct bpf_func_state *frame[MAX_CALL_FRAMES];
 	u32 curframe;
+	bool speculative;
 };
 
 #define bpf_get_spilled_reg(slot, frame)				\
@@ -167,15 +168,24 @@ struct bpf_verifier_state_list {
 	struct bpf_verifier_state_list *next;
 };
 
+/* Possible states for alu_state member. */
+#define BPF_ALU_SANITIZE_SRC		1U
+#define BPF_ALU_SANITIZE_DST		2U
+#define BPF_ALU_NEG_VALUE		(1U << 2)
+#define BPF_ALU_SANITIZE		(BPF_ALU_SANITIZE_SRC | \
+					 BPF_ALU_SANITIZE_DST)
+
 struct bpf_insn_aux_data {
 	union {
 		enum bpf_reg_type ptr_type;	/* pointer type for load/store insns */
 		unsigned long map_state;	/* pointer/poison value for maps */
 		s32 call_imm;			/* saved imm field of call insn */
+		u32 alu_limit;			/* limit for add/sub register with pointer */
 	};
 	int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
 	int sanitize_stack_off; /* stack slot to be cleared */
 	bool seen; /* this insn was processed by the verifier */
+	u8 alu_state; /* used in combination with alu_limit */
 };
 
 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */

@@ -710,6 +710,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 		free_func_state(dst_state->frame[i]);
 		dst_state->frame[i] = NULL;
 	}
+	dst_state->speculative = src->speculative;
 	dst_state->curframe = src->curframe;
 	for (i = 0; i <= src->curframe; i++) {
 		dst = dst_state->frame[i];
@@ -754,7 +755,8 @@ static int pop_stack(struct bpf_verifier_env *env, int *prev_insn_idx,
 }
 
 static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
-					     int insn_idx, int prev_insn_idx)
+					     int insn_idx, int prev_insn_idx,
+					     bool speculative)
 {
 	struct bpf_verifier_state *cur = env->cur_state;
 	struct bpf_verifier_stack_elem *elem;
@@ -772,6 +774,7 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
 	err = copy_verifier_state(&elem->st, cur);
 	if (err)
 		goto err;
+	elem->st.speculative |= speculative;
 	if (env->stack_size > BPF_COMPLEXITY_LIMIT_STACK) {
 		verbose(env, "BPF program is too complex\n");
 		goto err;
@@ -3067,6 +3070,102 @@ static bool check_reg_sane_offset(struct bpf_verifier_env *env,
 	return true;
 }
 
+static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env)
+{
+	return &env->insn_aux_data[env->insn_idx];
+}
+
+static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
+			      u32 *ptr_limit, u8 opcode, bool off_is_neg)
+{
+	bool mask_to_left = (opcode == BPF_ADD &&  off_is_neg) ||
+			    (opcode == BPF_SUB && !off_is_neg);
+	u32 off;
+
+	switch (ptr_reg->type) {
+	case PTR_TO_STACK:
+		off = ptr_reg->off + ptr_reg->var_off.value;
+		if (mask_to_left)
+			*ptr_limit = MAX_BPF_STACK + off;
+		else
+			*ptr_limit = -off;
+		return 0;
+	case PTR_TO_MAP_VALUE:
+		if (mask_to_left) {
+			*ptr_limit = ptr_reg->umax_value + ptr_reg->off;
+		} else {
+			off = ptr_reg->smin_value + ptr_reg->off;
+			*ptr_limit = ptr_reg->map_ptr->value_size - off;
+		}
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int sanitize_ptr_alu(struct bpf_verifier_env *env,
+			    struct bpf_insn *insn,
+			    const struct bpf_reg_state *ptr_reg,
+			    struct bpf_reg_state *dst_reg,
+			    bool off_is_neg)
+{
+	struct bpf_verifier_state *vstate = env->cur_state;
+	struct bpf_insn_aux_data *aux = cur_aux(env);
+	bool ptr_is_dst_reg = ptr_reg == dst_reg;
+	u8 opcode = BPF_OP(insn->code);
+	u32 alu_state, alu_limit;
+	struct bpf_reg_state tmp;
+	bool ret;
+
+	if (env->allow_ptr_leaks || BPF_SRC(insn->code) == BPF_K)
+		return 0;
+
+	/* We already marked aux for masking from non-speculative
+	 * paths, thus we got here in the first place. We only care
+	 * to explore bad access from here.
+	 */
+	if (vstate->speculative)
+		goto do_sim;
+
+	alu_state  = off_is_neg ? BPF_ALU_NEG_VALUE : 0;
+	alu_state |= ptr_is_dst_reg ?
+		     BPF_ALU_SANITIZE_SRC : BPF_ALU_SANITIZE_DST;
+
+	if (retrieve_ptr_limit(ptr_reg, &alu_limit, opcode, off_is_neg))
+		return 0;
+
+	/* If we arrived here from different branches with different
+	 * limits to sanitize, then this won't work.
+	 */
+	if (aux->alu_state &&
+	    (aux->alu_state != alu_state ||
+	     aux->alu_limit != alu_limit))
+		return -EACCES;
+
+	/* Corresponding fixup done in fixup_bpf_calls(). */
+	aux->alu_state = alu_state;
+	aux->alu_limit = alu_limit;
+
+do_sim:
+	/* Simulate and find potential out-of-bounds access under
+	 * speculative execution from truncation as a result of
+	 * masking when off was not within expected range. If off
+	 * sits in dst, then we temporarily need to move ptr there
+	 * to simulate dst (== 0) +/-= ptr. Needed, for example,
+	 * for cases where we use K-based arithmetic in one direction
+	 * and truncated reg-based in the other in order to explore
+	 * bad access.
+	 */
+	if (!ptr_is_dst_reg) {
+		tmp = *dst_reg;
+		*dst_reg = *ptr_reg;
+	}
+	ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true);
+	if (!ptr_is_dst_reg)
+		*dst_reg = tmp;
+	return !ret ? -EFAULT : 0;
+}
+
 /* Handles arithmetic on a pointer and a scalar: computes new min/max and var_off.
  * Caller should also handle BPF_MOV case separately.
  * If we return -EACCES, caller may want to try again treating pointer as a
@@ -3087,6 +3186,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 	    umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value;
 	u32 dst = insn->dst_reg, src = insn->src_reg;
 	u8 opcode = BPF_OP(insn->code);
+	int ret;
 
 	dst_reg = &regs[dst];
 
@@ -3142,6 +3242,11 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 
 	switch (opcode) {
 	case BPF_ADD:
+		ret = sanitize_ptr_alu(env, insn, ptr_reg, dst_reg, smin_val < 0);
+		if (ret < 0) {
+			verbose(env, "R%d tried to add from different maps or paths\n", dst);
+			return ret;
+		}
 		/* We can take a fixed offset as long as it doesn't overflow
 		 * the s32 'off' field
 		 */
@@ -3192,6 +3297,11 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 		}
 		break;
 	case BPF_SUB:
+		ret = sanitize_ptr_alu(env, insn, ptr_reg, dst_reg, smin_val < 0);
+		if (ret < 0) {
+			verbose(env, "R%d tried to sub from different maps or paths\n", dst);
+			return ret;
+		}
 		if (dst_reg == off_reg) {
 			/* scalar -= pointer.  Creates an unknown scalar */
 			verbose(env, "R%d tried to subtract pointer from scalar\n",
@@ -4389,7 +4499,8 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 		}
 	}
 
-	other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx);
+	other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx,
+				  false);
 	if (!other_branch)
 		return -EFAULT;
 	other_branch_regs = other_branch->frame[other_branch->curframe]->regs;
@@ -5499,6 +5610,12 @@ static bool states_equal(struct bpf_verifier_env *env,
 	if (old->curframe != cur->curframe)
 		return false;
 
+	/* Verification state from speculative execution simulation
+	 * must never prune a non-speculative execution one.
+	 */
+	if (old->speculative && !cur->speculative)
+		return false;
+
 	/* for states to be equal callsites have to be the same
 	 * and all frame states need to be equivalent
 	 */
@@ -5700,6 +5817,7 @@ static int do_check(struct bpf_verifier_env *env)
 	if (!state)
 		return -ENOMEM;
 	state->curframe = 0;
+	state->speculative = false;
 	state->frame[0] = kzalloc(sizeof(struct bpf_func_state), GFP_KERNEL);
 	if (!state->frame[0]) {
 		kfree(state);
@@ -5739,8 +5857,10 @@ static int do_check(struct bpf_verifier_env *env)
 			/* found equivalent state, can prune the search */
 			if (env->log.level) {
 				if (do_print_state)
-					verbose(env, "\nfrom %d to %d: safe\n",
-						env->prev_insn_idx, env->insn_idx);
+					verbose(env, "\nfrom %d to %d%s: safe\n",
+						env->prev_insn_idx, env->insn_idx,
+						env->cur_state->speculative ?
+						" (speculative execution)" : "");
 				else
 					verbose(env, "%d: safe\n", env->insn_idx);
 			}
@@ -5757,8 +5877,10 @@ static int do_check(struct bpf_verifier_env *env)
 			if (env->log.level > 1)
 				verbose(env, "%d:", env->insn_idx);
 			else
-				verbose(env, "\nfrom %d to %d:",
-					env->prev_insn_idx, env->insn_idx);
+				verbose(env, "\nfrom %d to %d%s:",
+					env->prev_insn_idx, env->insn_idx,
+					env->cur_state->speculative ?
+					" (speculative execution)" : "");
 			print_verifier_state(env, state->frame[state->curframe]);
 			do_print_state = false;
 		}
@@ -6750,6 +6872,57 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
 			continue;
 		}
 
+		if (insn->code == (BPF_ALU64 | BPF_ADD | BPF_X) ||
+		    insn->code == (BPF_ALU64 | BPF_SUB | BPF_X)) {
+			const u8 code_add = BPF_ALU64 | BPF_ADD | BPF_X;
+			const u8 code_sub = BPF_ALU64 | BPF_SUB | BPF_X;
+			struct bpf_insn insn_buf[16];
+			struct bpf_insn *patch = &insn_buf[0];
+			bool issrc, isneg;
+			u32 off_reg;
+
+			aux = &env->insn_aux_data[i + delta];
+			if (!aux->alu_state)
+				continue;
+
+			isneg = aux->alu_state & BPF_ALU_NEG_VALUE;
+			issrc = (aux->alu_state & BPF_ALU_SANITIZE) ==
+				BPF_ALU_SANITIZE_SRC;
+
+			off_reg = issrc ? insn->src_reg : insn->dst_reg;
+			if (isneg)
+				*patch++ = BPF_ALU64_IMM(BPF_MUL, off_reg, -1);
+			*patch++ = BPF_MOV32_IMM(BPF_REG_AX, aux->alu_limit - 1);
+			*patch++ = BPF_ALU64_REG(BPF_SUB, BPF_REG_AX, off_reg);
+			*patch++ = BPF_ALU64_REG(BPF_OR, BPF_REG_AX, off_reg);
+			*patch++ = BPF_ALU64_IMM(BPF_NEG, BPF_REG_AX, 0);
+			*patch++ = BPF_ALU64_IMM(BPF_ARSH, BPF_REG_AX, 63);
+			if (issrc) {
+				*patch++ = BPF_ALU64_REG(BPF_AND, BPF_REG_AX,
+							 off_reg);
+				insn->src_reg = BPF_REG_AX;
+			} else {
+				*patch++ = BPF_ALU64_REG(BPF_AND, off_reg,
+							 BPF_REG_AX);
+			}
+			if (isneg)
+				insn->code = insn->code == code_add ?
+					     code_sub : code_add;
+			*patch++ = *insn;
+			if (issrc && isneg)
+				*patch++ = BPF_ALU64_IMM(BPF_MUL, off_reg, -1);
+			cnt = patch - insn_buf;
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;
+
+			delta    += cnt - 1;
+			env->prog = prog = new_prog;
+			insn      = new_prog->insnsi + i + delta;
+			continue;
+		}
+
 		if (insn->code != (BPF_JMP | BPF_CALL))
 			continue;
 		if (insn->src_reg == BPF_PSEUDO_CALL)