[PATCH bpf-next 1/2] bpf: handle fake register spill to stack with BPF_ST_MEM instruction

[Andrii Nakryiko <andrii@kernel.org>]

When verifier validates BPF_ST_MEM instruction that stores known
constant to stack (e.g., *(u64 *)(r10 - 8) = 123), it effectively spills
a fake register with a constant (but initially imprecise) value to
a stack slot. Because read-side logic treats it as a proper register
fill from stack slot, we need to mark such stack slot initialization as
INSN_F_STACK_ACCESS instruction to stop precision backtracking from
missing it.

Fixes: 41f6f64e6999 ("bpf: support non-r10 register spill/fill to/from stack in precision tracking")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/bpf/verifier.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fb690539d5f6..727a59e4a647 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4498,7 +4498,6 @@ static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 		__mark_reg_known(&fake_reg, insn->imm);
 		fake_reg.type = SCALAR_VALUE;
 		save_register_state(env, state, spi, &fake_reg, size);
-		insn_flags = 0; /* not a register spill */
 	} else if (reg && is_spillable_regtype(reg->type)) {
 		/* register containing pointer is being spilled into stack */
 		if (size != BPF_REG_SIZE) {
-- 
2.34.1