[PATCH 5.11 121/122] bpf: Improve verifier error messages for users

Greg Kroah-Hartman
2021-04-19T13:17:21Z

From: Daniel Borkmann <daniel@iogearbox.net>

commit a6aaece00a57fa6f22575364b3903dfbccf5345d upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/verifier.c | 86 ++++++++++++++++++++++++++++++++++++--------------
1 file changed, 63 insertions(+), 23 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5384,6 +5384,14 @@ static struct bpf_insn_aux_data *cur_aux
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)
@@ -5395,7 +5403,7 @@ static int retrieve_ptr_limit(const stru

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:
@@ -5422,11 +5430,11 @@ static int retrieve_ptr_limit(const stru
}
break;
default:
- return -EINVAL;
+ return REASON_TYPE;
}

if (ptr_limit >= max)
- return -ERANGE;
+ return REASON_LIMIT;
*alu_limit = ptr_limit;
return 0;
}
@@ -5446,7 +5454,7 @@ static int update_alu_sanitation_state(s
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;
@@ -5519,7 +5527,46 @@ do_sim:
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;
}

/* Handles arithmetic on a pointer and a scalar: computes new min/max and var_off.
@@ -5609,10 +5656,9 @@ static int adjust_ptr_min_max_vals(struc
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
*/
@@ -5664,10 +5710,9 @@ static int adjust_ptr_min_max_vals(struc
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",
@@ -6357,9 +6402,8 @@ static int adjust_scalar_min_max_vals(st
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;
@@ -6418,20 +6462,16 @@ static int adjust_scalar_min_max_vals(st
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);