From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp153-165.sina.com.cn (smtp153-165.sina.com.cn [61.135.153.165]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 64FF6176AC8 for ; Thu, 31 Jul 2025 01:53:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=61.135.153.165 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753926828; cv=none; b=ce8U+8UB3GwiY8A5rrzc72be3UtgrWqxSyvKILbIjWQAbq1ITqxSWZRjXwk7f3BIJcly24GMWa/4hJ28gKA59pl96WHf0nm2Zlx9YalimEHNuXdPm2SxySn3/+DcLggUCYsnzxHxDk7A/Vrw7hhOLbuFJfwHiHOMKvTE/miwFM4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753926828; c=relaxed/simple; bh=o013fffBqmCmMLgo3PtHQdg7F8MxRApvjB+lgABcTJU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NsaXri4VM6JlvBUI2dZomHkEGsEYqN2DQg4mnv1xZR038JnR9CI/SuOQTzPPynTvZ5wEgqgaY76BWLC/N/0jiAEFnWXQTJu2bObRSF9lM0h1lx5tt/DDFgFfUGQpkVrIuFpDfC8/EMZZooUH0syN5UN+HjG3yShzoAkTHDok3IU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com; spf=pass smtp.mailfrom=sina.com; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b=TrYWBsEH; arc=none smtp.client-ip=61.135.153.165 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sina.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b="TrYWBsEH" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sina.com; s=201208; t=1753926819; bh=ROXTcu3NC59udh5UXJspljhoslQrPWl0Sx4aF8K9Emw=; h=From:Subject:Date:Message-ID; b=TrYWBsEHCEiIlC3XYaDXOSbsnHFXbWeHZtPps82kboCPxLEXSqIiGwmTha4O8q8iV Lt9IQTBYa1wEbNDe7B58rblY1f9+hxigiuZPbCyga+APyMj4rlTwRj4iOTnU1gcnI4 wkHccNLeTGZsQ2llyKHrYVd7ZQLQ9TADiLYTt1Ks= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([114.249.58.236]) by sina.com (10.54.253.32) with ESMTP id 688ACC73000065B1; Thu, 31 Jul 2025 09:52:53 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 9109934456634 X-SMAIL-UIID: E9F0BA989AA444DF88B0D3645AEDC517-20250731-095253-1 From: Hillf Danton To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, peterx@redhat.com, lokeshgidra@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot , stable@vger.kernel.org Subject: Re: [PATCH 1/1] userfaultfd: fix a crash when UFFDIO_MOVE handles a THP hole Date: Thu, 31 Jul 2025 09:52:40 +0800 Message-ID: <20250731015241.3576-1-hdanton@sina.com> In-Reply-To: <20250730170733.3829267-1-surenb@google.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit #syz test When UFFDIO_MOVE is used with UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES and it encounters a non-present THP, it fails to properly recognize an unmapped hole and tries to access a non-existent folio, resulting in a crash. Add a check to skip non-present THPs. Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ Signed-off-by: Suren Baghdasaryan Cc: stable@vger.kernel.org --- mm/userfaultfd.c | 38 +++++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 15 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index cbed91b09640..60be8080ddd0 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1818,27 +1818,35 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, ptl = pmd_trans_huge_lock(src_pmd, src_vma); if (ptl) { - /* Check if we can move the pmd without splitting it. */ - if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || - !pmd_none(dst_pmdval)) { - struct folio *folio = pmd_folio(*src_pmd); + if (pmd_present(*src_pmd) || is_pmd_migration_entry(*src_pmd)) { + /* Check if we can move the pmd without splitting it. */ + if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || + !pmd_none(dst_pmdval)) { + if (pmd_present(*src_pmd)) { + struct folio *folio = pmd_folio(*src_pmd); + + if (!folio || (!is_huge_zero_folio(folio) && + !PageAnonExclusive(&folio->page))) { + spin_unlock(ptl); + err = -EBUSY; + break; + } + } - if (!folio || (!is_huge_zero_folio(folio) && - !PageAnonExclusive(&folio->page))) { spin_unlock(ptl); - err = -EBUSY; - break; + split_huge_pmd(src_vma, src_pmd, src_addr); + /* The folio will be split by move_pages_pte() */ + continue; } + err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, + dst_pmdval, dst_vma, src_vma, + dst_addr, src_addr); + } else { + /* nothing to do to move a hole */ spin_unlock(ptl); - split_huge_pmd(src_vma, src_pmd, src_addr); - /* The folio will be split by move_pages_pte() */ - continue; + err = 0; } - - err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, - dst_pmdval, dst_vma, src_vma, - dst_addr, src_addr); step_size = HPAGE_PMD_SIZE; } else { if (pmd_none(*src_pmd)) { base-commit: 01da54f10fddf3b01c5a3b80f6b16bbad390c302 -- 2.50.1.552.g942d659e1b-goog