bpf: correct slot_type marking logic to allow more stack slot sharing
Verifier is supposed to support sharing stack slot allocated to ptr with
SCALAR_VALUE for privileged program. However this doesn't happen for some
cases.
The reason is verifier is not clearing slot_type STACK_SPILL for all bytes,
it only clears part of them, while verifier is using:
slot_type[0] == STACK_SPILL
as a convention to check one slot is ptr type.
So, the consequence of partial clearing slot_type is verifier could treat a
partially overridden ptr slot, which should now be a SCALAR_VALUE slot,
still as ptr slot, and rejects some valid programs.
Before this patch, test_xdp_noinline.o under bpf selftests, bpf_lxc.o and
bpf_netdev.o under Cilium bpf repo, when built with -mattr=+alu32 are
rejected due to this issue. After this patch, they all accepted.
There is no processed insn number change before and after this patch on
Cilium bpf programs.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0125731..e0e77ff 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1286,6 +1286,10 @@ static int check_stack_write(struct bpf_verifier_env *env,
/* regular write of data into stack destroys any spilled ptr */
state->stack[spi].spilled_ptr.type = NOT_INIT;
+ /* Mark slots as STACK_MISC if they belonged to spilled ptr. */
+ if (state->stack[spi].slot_type[0] == STACK_SPILL)
+ for (i = 0; i < BPF_REG_SIZE; i++)
+ state->stack[spi].slot_type[i] = STACK_MISC;
/* only mark the slot as written if all 8 bytes were written
* otherwise read propagation may incorrectly stop too soon
@@ -1303,6 +1307,7 @@ static int check_stack_write(struct bpf_verifier_env *env,
register_is_null(&cur->regs[value_regno]))
type = STACK_ZERO;
+ /* Mark slots affected by this stack write. */
for (i = 0; i < size; i++)
state->stack[spi].slot_type[(slot - i) % BPF_REG_SIZE] =
type;
