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: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 21 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e37e06b1229d..339c8a1371de 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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