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Commit a9789ef9 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

bpf: properly reset caller saved regs after helper call and ld_abs/ind 



Currently, after performing helper calls, we clear all caller saved
registers, that is r0 - r5 and fill r0 depending on struct bpf_func_proto
specification. The way we reset these regs can affect pruning decisions
in later paths, since we only reset register's imm to 0 and type to
NOT_INIT. However, we leave out clearing of other variables such as id,
min_value, max_value, etc, which can later on lead to pruning mismatches
due to stale data.

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1ad2f583

kernel/bpf/verifier.c

+16 −21
Original line number Diff line number Diff line
@@ -463,19 +463,22 @@ static const int caller_saved[CALLER_SAVED_REGS] = { 
	BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5

};



static void mark_reg_not_init(struct bpf_reg_state *regs, u32 regno)

{

	BUG_ON(regno >= MAX_BPF_REG);



	memset(&regs[regno], 0, sizeof(regs[regno]));

	regs[regno].type = NOT_INIT;

	regs[regno].min_value = BPF_REGISTER_MIN_RANGE;

	regs[regno].max_value = BPF_REGISTER_MAX_RANGE;

}



static void init_reg_state(struct bpf_reg_state *regs)

{

	int i;



	for (i = 0; i < MAX_BPF_REG; i++) {

		regs[i].type = NOT_INIT;

		regs[i].imm = 0;

		regs[i].min_value = BPF_REGISTER_MIN_RANGE;

		regs[i].max_value = BPF_REGISTER_MAX_RANGE;

		regs[i].min_align = 0;

		regs[i].aux_off = 0;

		regs[i].aux_off_align = 0;

	}

	for (i = 0; i < MAX_BPF_REG; i++)

		mark_reg_not_init(regs, i);



	/* frame pointer */

	regs[BPF_REG_FP].type = FRAME_PTR;
@@ -1346,7 +1349,6 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx) 
	struct bpf_verifier_state *state = &env->cur_state;

	const struct bpf_func_proto *fn = NULL;

	struct bpf_reg_state *regs = state->regs;

	struct bpf_reg_state *reg;

	struct bpf_call_arg_meta meta;

	bool changes_data;

	int i, err;
@@ -1413,11 +1415,8 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx) 
	}



	/* reset caller saved regs */

	for (i = 0; i < CALLER_SAVED_REGS; i++) {

		reg = regs + caller_saved[i];

		reg->type = NOT_INIT;

		reg->imm = 0;

	}

	for (i = 0; i < CALLER_SAVED_REGS; i++)

		mark_reg_not_init(regs, caller_saved[i]);



	/* update return register */

	if (fn->ret_type == RET_INTEGER) {
@@ -2445,7 +2444,6 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn) 
{

	struct bpf_reg_state *regs = env->cur_state.regs;

	u8 mode = BPF_MODE(insn->code);

	struct bpf_reg_state *reg;

	int i, err;



	if (!may_access_skb(env->prog->type)) {
@@ -2478,11 +2476,8 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn) 
	}



	/* reset caller saved regs to unreadable */

	for (i = 0; i < CALLER_SAVED_REGS; i++) {

		reg = regs + caller_saved[i];

		reg->type = NOT_INIT;

		reg->imm = 0;

	}

	for (i = 0; i < CALLER_SAVED_REGS; i++)

		mark_reg_not_init(regs, caller_saved[i]);



	/* mark destination R0 register as readable, since it contains

	 * the value fetched from the packet