Revert "bpf: Reject indirect var_off stack access in unpriv mode"

ANBZ: torvalds#342

This reverts commit e232808.

Signed-off-by: Qiao Ma <mqaio@linux.alibaba.com>
Acked-by: Mao Wenan <wenan.mao@linux.alibaba.com>
Acked-by: Tony Lu <tonylu@linux.alibaba.com>

kernel/bpf/verifier.c

@@ -1812,19 +1812,6 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
 		if (err)
 			return err;
 	} else {
-		/* Variable offset is prohibited for unprivileged mode for
-		 * simplicity since it requires corresponding support in
-		 * Spectre masking for stack ALU.
-		 * See also retrieve_ptr_limit().
-		 */
-		if (!env->allow_ptr_leaks) {
-			char tn_buf[48];
-
-			tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
-			verbose(env, "R%d indirect variable offset stack access prohibited for !root, var_off=%s\n",
-				regno, tn_buf);
-			return -EACCES;
-		}
 		/* Only initialized buffer on stack is allowed to be accessed
 		 * with variable offset. With uninitialized buffer it's hard to
 		 * guarantee that whole memory is marked as initialized on