From: Andrii Nakryiko <andrii@kernel.org>
To: <bpf@vger.kernel.org>, <ast@kernel.org>, <daniel@iogearbox.net>,
<martin.lau@kernel.org>
Cc: <andrii@kernel.org>, <kernel-team@meta.com>,
Eduard Zingerman <eddyz87@gmail.com>,
Shung-Hsi Yu <shung-hsi.yu@suse.com>
Subject: [PATCH v4 bpf-next 04/11] bpf: enforce exact retval range on subprog/callback exit
Date: Fri, 1 Dec 2023 10:33:52 -0800 [thread overview]
Message-ID: <20231201183359.1769668-5-andrii@kernel.org> (raw)
In-Reply-To: <20231201183359.1769668-1-andrii@kernel.org>
Instead of relying on potentially imprecise tnum representation of
expected return value range for callbacks and subprogs, validate that
smin/smax range satisfy exact expected range of return values.
E.g., if callback would need to return [0, 2] range, tnum can't
represent this precisely and instead will allow [0, 3] range. By
checking smin/smax range, we can make sure that subprog/callback indeed
returns only valid [0, 2] range.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
include/linux/bpf_verifier.h | 7 ++++++-
kernel/bpf/verifier.c | 33 ++++++++++++++++++++++-----------
2 files changed, 28 insertions(+), 12 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 0c0e1bccad45..3378cc753061 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -275,6 +275,11 @@ struct bpf_reference_state {
int callback_ref;
};
+struct bpf_retval_range {
+ s32 minval;
+ s32 maxval;
+};
+
/* state of the program:
* type of all registers and stack info
*/
@@ -297,7 +302,7 @@ struct bpf_func_state {
* void foo(void) { bpf_timer_set_callback(,foo); }
*/
u32 async_entry_cnt;
- struct tnum callback_ret_range;
+ struct bpf_retval_range callback_ret_range;
bool in_callback_fn;
bool in_async_callback_fn;
bool in_exception_callback_fn;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 849fbf47b5f3..f3d9d7de68da 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2305,6 +2305,11 @@ static void init_reg_state(struct bpf_verifier_env *env,
regs[BPF_REG_FP].frameno = state->frameno;
}
+static struct bpf_retval_range retval_range(s32 minval, s32 maxval)
+{
+ return (struct bpf_retval_range){ minval, maxval };
+}
+
#define BPF_MAIN_FUNC (-1)
static void init_func_state(struct bpf_verifier_env *env,
struct bpf_func_state *state,
@@ -2313,7 +2318,7 @@ static void init_func_state(struct bpf_verifier_env *env,
state->callsite = callsite;
state->frameno = frameno;
state->subprogno = subprogno;
- state->callback_ret_range = tnum_range(0, 0);
+ state->callback_ret_range = retval_range(0, 0);
init_reg_state(env, state);
mark_verifier_state_scratched(env);
}
@@ -9396,7 +9401,7 @@ static int set_map_elem_callback_state(struct bpf_verifier_env *env,
return err;
callee->in_callback_fn = true;
- callee->callback_ret_range = tnum_range(0, 1);
+ callee->callback_ret_range = retval_range(0, 1);
return 0;
}
@@ -9418,7 +9423,7 @@ static int set_loop_callback_state(struct bpf_verifier_env *env,
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_callback_fn = true;
- callee->callback_ret_range = tnum_range(0, 1);
+ callee->callback_ret_range = retval_range(0, 1);
return 0;
}
@@ -9448,7 +9453,7 @@ static int set_timer_callback_state(struct bpf_verifier_env *env,
__mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_async_callback_fn = true;
- callee->callback_ret_range = tnum_range(0, 1);
+ callee->callback_ret_range = retval_range(0, 1);
return 0;
}
@@ -9476,7 +9481,7 @@ static int set_find_vma_callback_state(struct bpf_verifier_env *env,
__mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_callback_fn = true;
- callee->callback_ret_range = tnum_range(0, 1);
+ callee->callback_ret_range = retval_range(0, 1);
return 0;
}
@@ -9499,7 +9504,7 @@ static int set_user_ringbuf_callback_state(struct bpf_verifier_env *env,
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_callback_fn = true;
- callee->callback_ret_range = tnum_range(0, 1);
+ callee->callback_ret_range = retval_range(0, 1);
return 0;
}
@@ -9531,7 +9536,7 @@ static int set_rbtree_add_callback_state(struct bpf_verifier_env *env,
__mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_callback_fn = true;
- callee->callback_ret_range = tnum_range(0, 1);
+ callee->callback_ret_range = retval_range(0, 1);
return 0;
}
@@ -9560,6 +9565,11 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
return is_rbtree_lock_required_kfunc(kfunc_btf_id);
}
+static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
+{
+ return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
+}
+
static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
{
struct bpf_verifier_state *state = env->cur_state, *prev_st;
@@ -9583,9 +9593,6 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
caller = state->frame[state->curframe - 1];
if (callee->in_callback_fn) {
- /* enforce R0 return value range [0, 1]. */
- struct tnum range = callee->callback_ret_range;
-
if (r0->type != SCALAR_VALUE) {
verbose(env, "R0 not a scalar value\n");
return -EACCES;
@@ -9597,7 +9604,11 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
if (err)
return err;
- if (!tnum_in(range, r0->var_off)) {
+ /* enforce R0 return value range */
+ if (!retval_range_within(callee->callback_ret_range, r0)) {
+ struct tnum range = tnum_range(callee->callback_ret_range.minval,
+ callee->callback_ret_range.maxval);
+
verbose_invalid_scalar(env, r0, &range, "callback return", "R0");
return -EINVAL;
}
--
2.34.1
next prev parent reply other threads:[~2023-12-01 18:34 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-01 18:33 [PATCH v4 bpf-next 00/11] BPF verifier retval logic fixes Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 01/11] bpf: rearrange bpf_func_state fields to save a bit of memory Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 02/11] bpf: provide correct register name for exception callback retval check Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 03/11] bpf: enforce precision of R0 on callback return Andrii Nakryiko
2023-12-01 18:33 ` Andrii Nakryiko [this message]
2023-12-01 18:33 ` [PATCH v4 bpf-next 05/11] selftests/bpf: add selftest validating callback result is enforced Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 06/11] bpf: enforce precise retval range on program exit Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 07/11] bpf: unify async callback and program retval checks Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 08/11] bpf: enforce precision of R0 on program/async callback return Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 09/11] selftests/bpf: validate async callback return value check correctness Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 10/11] selftests/bpf: adjust global_func15 test to validate prog exit precision Andrii Nakryiko
2023-12-01 18:33 ` [PATCH v4 bpf-next 11/11] bpf: simplify tnum output if a fully known constant Andrii Nakryiko
2023-12-01 20:11 ` [PATCH v4 bpf-next 00/11] BPF verifier retval logic fixes Andrii Nakryiko
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