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bpf: Improve verifier error messages for users 

Consolidate all error handling and provide more user-friendly error messages
from sanitize_ptr_alu() and sanitize_val_alu().

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2021-03-23 09:30:01 +01:00
parent b658bbb844
commit a6aaece00a
1 changed files with 63 additions and 23 deletions
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86
kernel/bpf/verifier.c
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@ -5856,6 +5856,14 @@ static struct bpf_insn_aux_data *cur_aux(struct bpf_verifier_env *env)
return &env->insn_aux_data[env->insn_idx];
}
enum {
REASON_BOUNDS = -1,
REASON_TYPE = -2,
REASON_PATHS = -3,
REASON_LIMIT = -4,
REASON_STACK = -5,
};
static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
const struct bpf_reg_state *off_reg,
u32 *alu_limit, u8 opcode)
@ -5867,7 +5875,7 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
if (!tnum_is_const(off_reg->var_off) &&
(off_reg->smin_value < 0) != (off_reg->smax_value < 0))
return -EACCES;
return REASON_BOUNDS;
switch (ptr_reg->type) {
case PTR_TO_STACK:
@ -5894,11 +5902,11 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg,
}
break;
default:
return -EINVAL;
return REASON_TYPE;
}
if (ptr_limit >= max)
return -ERANGE;
return REASON_LIMIT;
*alu_limit = ptr_limit;
return 0;
}
@ -5918,7 +5926,7 @@ static int update_alu_sanitation_state(struct bpf_insn_aux_data *aux,
if (aux->alu_state &&
(aux->alu_state != alu_state ||
aux->alu_limit != alu_limit))
return -EACCES;
return REASON_PATHS;
/* Corresponding fixup done in fixup_bpf_calls(). */
aux->alu_state = alu_state;
@ -5991,7 +5999,46 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env,
ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true);
if (!ptr_is_dst_reg && ret)
*dst_reg = tmp;
return !ret ? -EFAULT : 0;
return !ret ? REASON_STACK : 0;
}
static int sanitize_err(struct bpf_verifier_env *env,
const struct bpf_insn *insn, int reason,
const struct bpf_reg_state *off_reg,
const struct bpf_reg_state *dst_reg)
{
static const char *err = "pointer arithmetic with it prohibited for !root";
const char *op = BPF_OP(insn->code) == BPF_ADD ? "add" : "sub";
u32 dst = insn->dst_reg, src = insn->src_reg;
switch (reason) {
case REASON_BOUNDS:
verbose(env, "R%d has unknown scalar with mixed signed bounds, %s\n",
off_reg == dst_reg ? dst : src, err);
break;
case REASON_TYPE:
verbose(env, "R%d has pointer with unsupported alu operation, %s\n",
off_reg == dst_reg ? src : dst, err);
break;
case REASON_PATHS:
verbose(env, "R%d tried to %s from different maps, paths or scalars, %s\n",
dst, op, err);
break;
case REASON_LIMIT:
verbose(env, "R%d tried to %s beyond pointer bounds, %s\n",
dst, op, err);
break;
case REASON_STACK:
verbose(env, "R%d could not be pushed for speculative verification, %s\n",
dst, err);
break;
default:
verbose(env, "verifier internal error: unknown reason (%d)\n",
reason);
break;
}
return -EACCES;
}
/* check that stack access falls within stack limits and that 'reg' doesn't
@ -6116,10 +6163,9 @@ 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, off_reg, dst_reg);
if (ret < 0) {
verbose(env, "R%d tried to add from different maps, paths, or prohibited types\n", dst);
return ret;
}
if (ret < 0)
return sanitize_err(env, insn, ret, off_reg, dst_reg);
/* We can take a fixed offset as long as it doesn't overflow
* the s32 'off' field
*/
@ -6171,10 +6217,9 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
break;
case BPF_SUB:
ret = sanitize_ptr_alu(env, insn, ptr_reg, off_reg, dst_reg);
if (ret < 0) {
verbose(env, "R%d tried to sub from different maps, paths, or prohibited types\n", dst);
return ret;
}
if (ret < 0)
return sanitize_err(env, insn, ret, off_reg, dst_reg);
if (dst_reg == off_reg) {
/* scalar -= pointer. Creates an unknown scalar */
verbose(env, "R%d tried to subtract pointer from scalar\n",
@ -6863,9 +6908,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
s32 s32_min_val, s32_max_val;
u32 u32_min_val, u32_max_val;
u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
u32 dst = insn->dst_reg;
int ret;
bool alu32 = (BPF_CLASS(insn->code) != BPF_ALU64);
int ret;
smin_val = src_reg.smin_value;
smax_val = src_reg.smax_value;
@ -6924,20 +6968,16 @@ 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 (ret < 0)
return sanitize_err(env, insn, ret, NULL, NULL);
scalar32_min_max_add(dst_reg, &src_reg);
scalar_min_max_add(dst_reg, &src_reg);
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 (ret < 0)
return sanitize_err(env, insn, ret, NULL, NULL);
scalar32_min_max_sub(dst_reg, &src_reg);
scalar_min_max_sub(dst_reg, &src_reg);
dst_reg->var_off = tnum_sub(dst_reg->var_off, src_reg.var_off);