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>
Subject: [PATCH v2 bpf-next 06/10] bpf: preserve constant zero when doing partial register restore
Date: Mon, 20 Nov 2023 16:22:17 -0800 [thread overview]
Message-ID: <20231121002221.3687787-7-andrii@kernel.org> (raw)
In-Reply-To: <20231121002221.3687787-1-andrii@kernel.org>
Similar to special handling of STACK_ZERO, when reading 1/2/4 bytes from
stack from slot that has register spilled into it and that register has
a constant value zero, preserve that zero and mark spilled register as
precise for that. This makes spilled const zero register and STACK_ZERO
cases equivalent in their behavior.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/bpf/verifier.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5145afb5da25..00e6b17b71d0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4695,22 +4695,39 @@ static int check_stack_read_fixed_off(struct bpf_verifier_env *env,
copy_register_state(&state->regs[dst_regno], reg);
state->regs[dst_regno].subreg_def = subreg_def;
} else {
+ int spill_cnt = 0, zero_cnt = 0;
+
for (i = 0; i < size; i++) {
type = stype[(slot - i) % BPF_REG_SIZE];
- if (type == STACK_SPILL)
+ if (type == STACK_SPILL) {
+ spill_cnt++;
continue;
+ }
if (type == STACK_MISC)
continue;
- if (type == STACK_ZERO)
+ if (type == STACK_ZERO) {
+ zero_cnt++;
continue;
+ }
if (type == STACK_INVALID && env->allow_uninit_stack)
continue;
verbose(env, "invalid read from stack off %d+%d size %d\n",
off, i, size);
return -EACCES;
}
- mark_reg_unknown(env, state->regs, dst_regno);
- insn_flags = 0; /* not restoring original register state */
+
+ if (spill_cnt == size &&
+ tnum_is_const(reg->var_off) && reg->var_off.value == 0) {
+ __mark_reg_const_zero(&state->regs[dst_regno]);
+ /* this IS register fill, so keep insn_flags */
+ } else if (zero_cnt == size) {
+ /* similarly to mark_reg_stack_read(), preserve zeroes */
+ __mark_reg_const_zero(&state->regs[dst_regno]);
+ insn_flags = 0; /* not restoring original register state */
+ } else {
+ mark_reg_unknown(env, state->regs, dst_regno);
+ insn_flags = 0; /* not restoring original register state */
+ }
}
state->regs[dst_regno].live |= REG_LIVE_WRITTEN;
} else if (dst_regno >= 0) {
--
2.34.1
next prev parent reply other threads:[~2023-11-21 0:22 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-21 0:22 [PATCH v2 bpf-next 00/10] Complete BPF verifier precision tracking support for register spills Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 01/10] bpf: support non-r10 register spill/fill to/from stack in precision tracking Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 02/10] selftests/bpf: add stack access precision test Andrii Nakryiko
2023-11-21 0:42 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 03/10] bpf: fix check for attempt to corrupt spilled pointer Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 04/10] bpf: preserve STACK_ZERO slots on partial reg spills Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 05/10] selftests/bpf: validate STACK_ZERO is preserved on subreg spill Andrii Nakryiko
2023-11-21 0:55 ` Eduard Zingerman
2023-11-21 0:22 ` Andrii Nakryiko [this message]
2023-11-21 16:20 ` [PATCH v2 bpf-next 06/10] bpf: preserve constant zero when doing partial register restore Eduard Zingerman
2023-11-21 18:14 ` Andrii Nakryiko
2023-11-21 20:22 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 07/10] selftests/bpf: validate zero preservation for sub-slot loads Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman
2023-11-21 18:15 ` Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 08/10] bpf: track aligned STACK_ZERO cases as imprecise spilled registers Andrii Nakryiko
2023-11-21 20:38 ` Alexei Starovoitov
2023-11-21 22:01 ` Andrii Nakryiko
2023-11-21 0:22 ` [PATCH v2 bpf-next 09/10] selftests/bpf: validate precision logic in partial_stack_load_preserves_zeros Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman
2023-11-21 0:22 ` [PATCH v2 bpf-next 10/10] bpf: use common instruction history across all states Andrii Nakryiko
2023-11-21 16:20 ` Eduard Zingerman
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