[PATCH bpf-next 1/2] bpf: Record each half of a paired return value in verifier diagnostics

[Yonghong Song <yonghong.song@linux.dev>]

A subprogram returning more than 8 bytes comes back in the R0:R2 register
pair, and prepare_func_exit() copies both registers into the caller. The
diagnostic modification scope around that copy names only R0, so the write
into R2 is never recorded.

Fix it by opening a diagnostic modification scope for each return register.
This way, both return registers are recorded.

Fixes: 0630ad00d96d ("bpf: Add verifier support for 16-byte returns in R0: R2")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/verifier.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e036ae20bf6b..9aa29c367008 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10403,10 +10403,14 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 		 * return to the caller whatever the callee had in the
 		 * return register(s)
 		 */
-		bpf_diag_mod_begin(env, &caller->regs[BPF_REG_0], r0, BPF_DIAG_MOD_WRITE);
-		for (i = 0; i < nregs; i++)
-			caller->regs[ret_regs[i]] = callee->regs[ret_regs[i]];
-		bpf_diag_mod_end(env);
+		for (i = 0; i < nregs; i++) {
+			u32 regno = ret_regs[i];
+
+			bpf_diag_mod_begin(env, &caller->regs[regno], &callee->regs[regno],
+					   BPF_DIAG_MOD_WRITE);
+			caller->regs[regno] = callee->regs[regno];
+			bpf_diag_mod_end(env);
+		}
 	}
 
 	/* for callbacks like bpf_loop or bpf_for_each_map_elem go back to callsite,
-- 
2.53.0-Meta