From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f201.google.com (mail-pg1-f201.google.com [209.85.215.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 464994409 for ; Wed, 30 Jul 2025 17:07:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753895258; cv=none; b=OA2dxNJ1z6HMWfvDJoZfJ6M2IJWvRH0p2xS6TpJDdQ9MCLV7hjKF8lvENjeUYlYTCT8AbNLQcuCrR7oPBvrDYwNaYvF5FYDovawgWtD/p9I8tru2xqKD8kHnFARLG3atsf+CCd3IaeIK+37zkpYMYHid2LKqTY/gkBdWD2avmjk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753895258; c=relaxed/simple; bh=DX1GHJEw+yV3RRzbL6bG3xAge8rpg3j/1QwDNAVuivQ=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=MHQnJUyAGtL5lAbnpqjfjYDcUIBX/sh+OAizpzVKC0g88G/rm7q6ZOJ5QyhunKrVrXdkcHvdJWcUFs1ZqByGlY9xD2QxJOjJCmEpVaYvSu6IG4t3C65qMVB+qlUCPLM6OglXFJgGP5E77JuguDtpOKtuVQcphRiaCdrKZ8rHtOc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--surenb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ZBsuf+cs; arc=none smtp.client-ip=209.85.215.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--surenb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ZBsuf+cs" Received: by mail-pg1-f201.google.com with SMTP id 41be03b00d2f7-b42249503c4so367303a12.0 for ; Wed, 30 Jul 2025 10:07:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753895256; x=1754500056; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=iwvX/+FCFrBIkeHTGaFzh+izLhsSIPbGbCbxZr6W88I=; b=ZBsuf+csfQxlgG2dSBYTLs1gPALrU6SoJDDl9czF8f/3d8IZ9IsaGKAhNBhVxN+V/N FnSSSzzQ1jCuWK+GoYb8h/bBNpNv7RXpgoaYtOovvmPHfZaStEhPocDnEyxW1OhJPafi LgcxVUvx+1Uz5J3D07ZAG5Oc+YYyjE9Um2Q/ZrzCfL0TyIILLAAWmEaQxqM2Dg8O7deE yKIhPMDHf9AEOVMiDcNuDp8cnPnu7h8QSW+tasDYTVGWvoYtptTByYdIkP4wN1IZgORk XZ3Nvk3Ae8HGPeOnXKnUpt4IqW2w9x0qlJ2ZQto1xx5AZZjD7mi1yWv55LkHj5sU/HLh QDbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753895256; x=1754500056; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=iwvX/+FCFrBIkeHTGaFzh+izLhsSIPbGbCbxZr6W88I=; b=OXaNC7whZuVHhl3FPuhSOwulr8eg5eYn56eOQMhkzVPUfLxjAqfZijKNlIUOtN4lCC WIbklmlk2aRT2g/b7weKU/VMtozZka1W/gseg0Wu0WHTwS0qi0dyXXz9NjZR1YSuplLs ySmliafctZquzxVPBKHrZa495mi4XLBqAU5QWbxCJBEJr/kWukjPyeT6R55xr+iC6bzE KiNKE6KwEX4HKh3ue7orswiiR/sEkaggrbN9ZSH4MyM0SRxoEOjsUHj5lbSg1V49MYYD UEpg8jLgI4Qh63pkhnNdc9NwzgSzgvCgN2Tv8T/ArSybu/uFktOuLwCTJgyvTVk7gNF6 jl+w== X-Forwarded-Encrypted: i=1; AJvYcCUW6v515BrqouW+RZT56GThDrGYf4I6VxdYdJGazN/wO52xHVNZTPh9CPv8CO65q5xs0ETtMFyPgjLB5uM=@vger.kernel.org X-Gm-Message-State: AOJu0YzHkMwYu9+szhDZlIPUXMq/jsnTLLipeernffZRZZLuk1QfL4CN Sf2DmiBp3BlfrgMYeRD1fdzBc9rszlSPJ2lillnkOq4OuRw8Vi9l4mR+4o5aMYdIboL1A61ZNtD b1Fu0/g== X-Google-Smtp-Source: AGHT+IFRpqzleLfhY584F3gS5nWpI1NhhfzwuIDnKy5qdpfvKqCIZN9aFroMt2PQhlQ+ZIOuvhwlGyX2lGc= X-Received: from pjee12.prod.google.com ([2002:a17:90b:578c:b0:313:246f:8d54]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:f54c:b0:240:b884:2fa0 with SMTP id d9443c01a7336-240b8843050mr21999235ad.26.1753895256448; Wed, 30 Jul 2025 10:07:36 -0700 (PDT) Date: Wed, 30 Jul 2025 10:07:33 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.50.1.552.g942d659e1b-goog Message-ID: <20250730170733.3829267-1-surenb@google.com> Subject: [PATCH 1/1] userfaultfd: fix a crash when UFFDIO_MOVE handles a THP hole From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: peterx@redhat.com, david@redhat.com, aarcange@redhat.com, lokeshgidra@google.com, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" 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