Short answer. Just what came up on direct. Rule 132, Section 13 says a declared hostile witness "may also be impeached and cross-examined by the adverse party, but such cross-examination must only be on the subject matter of his or her examination-in-chief." The other side cannot use the opportunity to question the witness about unrelated matters.
What the law says
He or she may also be impeached and cross-examined by the adverse party, but such cross-examination must only be on the subject matter of his or her examination-in-chief.
Rule 132, Section 13 — Party may not impeach his or her own witness. Read the full provision →
What the law says
A witness may be considered as unwilling or hostile only if so declared by the court upon adequate showing of his or her adverse interest, unjustified reluctance to testify, or his or her having misled the party into calling him or her to the witness stand.
Rule 132, Section 13 — Party may not impeach his or her own witness. Read the full provision →
A witness does not become "hostile" on your say-so
Before any of this applies, the witness has to be formally declared hostile by the court. Rule 132, Section 13 provides that "a witness may be considered as unwilling or hostile only if so declared by the court upon adequate showing of his or her adverse interest, unjustified reluctance to testify, or his or her having misled the party into calling him or her to the witness stand." Simply being uncooperative or giving unhelpful answers on the stand is not enough — the party presenting the witness has to ask the court to make that declaration, and the court has to be satisfied one of those specific grounds exists.
What the declaration allows your own side to do
Once a witness is declared hostile, the rule lets the party who presented that witness treat them "in all respects as if he or she had been called by the adverse party, except by evidence of his or her bad character." In practice, this means the presenting party can impeach their own witness — something ordinarily not allowed under this same section, which otherwise bars "the party presenting the witness ... to impeach his or her credibility." The one carve-out is that bad character evidence still cannot be used, even against a witness who has been declared hostile.
The adverse party's cross-examination is scope-limited
This is the part that answers the question directly. The rule also lets the adverse party cross-examine a hostile witness, but it draws a firm boundary around that questioning: it "must only be on the subject matter of his or her examination-in-chief." Examination-in-chief is the direct testimony the witness gave when first questioned. So whatever the witness testified about on direct sets the outer limit — the adverse party cannot use the cross-examination to open up new topics that were never raised in that testimony.
Why the limit exists
This scope restriction keeps the cross-examination tethered to what was actually put before the court through the witness's own testimony, rather than turning it into an open-ended examination on any subject the adverse party wishes to raise. Even though a hostile witness ends up being questioned somewhat like the adverse party's own witness once the declaration is made, Section 13 does not erase the basic structure of the proceeding — the witness was still called and questioned first by the presenting party, and the cross-examination that follows stays anchored to that original subject matter.