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Message-Id: <20210430141911.295796543@linuxfoundation.org>
Date: Fri, 30 Apr 2021 16:20:18 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
bpf@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Frank van der Linden <fllinden@...zon.com>
Subject: [PATCH 5.4 4/8] bpf: Improve verifier error messages for users
From: Daniel Borkmann <daniel@...earbox.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@...earbox.net>
Reviewed-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Alexei Starovoitov <ast@...nel.org>
[fllinden@...zon.com: backport to 5.4]
Signed-off-by: Frank van der Linden <fllinden@...zon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
kernel/bpf/verifier.c | 84 ++++++++++++++++++++++++++++++++++++--------------
1 file changed, 62 insertions(+), 22 deletions(-)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4263,6 +4263,14 @@ 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)
@@ -4274,7 +4282,7 @@ 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:
@@ -4301,11 +4309,11 @@ 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;
}
@@ -4325,7 +4333,7 @@ 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;
@@ -4398,7 +4406,46 @@ 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.
@@ -4480,10 +4527,9 @@ 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
*/
@@ -4535,10 +4581,9 @@ 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",
@@ -4655,7 +4700,6 @@ static int adjust_scalar_min_max_vals(st
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) {
@@ -4692,10 +4736,8 @@ 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);
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;
@@ -4716,10 +4758,8 @@ static int adjust_scalar_min_max_vals(st
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);
if (signed_sub_overflows(dst_reg->smin_value, smax_val) ||
signed_sub_overflows(dst_reg->smax_value, smin_val)) {
/* Overflow possible, we know nothing */
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