From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (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 A980AD515 for ; Thu, 31 Jul 2025 15:44:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753976687; cv=none; b=iI9SAGSo89APioIEKrSx17KavpPhRoBH/tWfINFkri9H0hMJFlOwP3G3aUVgADgInl602Z27Y1lc5knEQClTI7bk+ObX2dR2IcqHi8stZkfR0kb87L2qYV/mre2wl9DXeVQ53Ri2c8Agn3r1vlrYboLcidhZwBe65eT7I4SJYoY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753976687; c=relaxed/simple; bh=OTA2x4bKnGUx3VAQlS2BrqHpdMgIv8m6sktHVnnjfbY=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=bdUhi5DW8uzr1ojFyvhCqOmkNkd9gHrBtpSi2QJazQdVfgJRj6UBFYQe9cYnst2NUND0fJ/7Nmxvkgti/5Fd6N9cCr1nd/kQwAHwjubWXyG+rcCwoN+LBddoGASZhTbZC3gpxvMu51zB4obQxaeL0v2iEwYnvM4AtWXQWA7Fpd8= 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=elLu8CEu; arc=none smtp.client-ip=209.85.215.202 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="elLu8CEu" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-b31ca4b6a8eso403030a12.1 for ; Thu, 31 Jul 2025 08:44:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753976685; x=1754581485; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=8D6H3TovcRUpDHrrv443Wy2kKrliHPbwf72lIkroPTg=; b=elLu8CEuxWIkjFWmb6U2eUeRTAVWvwFtNbf204tcWhPfNHxvOu3cj/67UsAD68naVh 80EvcDN0CTyh2tpNpOlcTk0AvxV2l58Lf/9yyPFN8+E7zCHzVaObjx0GQdZGdu5DCWIl RjTTsM2DGpYwkJf9J3oCTq+vOsjPS4cZgz1xi81YrWkwj6tAnNtxa5rLOLCreZpGKVFl UqJWIouJ4EfDIOqO6giMxZtskNjqKjiwoUUCj6x09x5wBau34IzgAyDIE8zRAzqgQMax qeaoCfEBYqSgTHH9xeu/5i+7ul1Rmp8tp7scEEcWkYWN3zH6D+dXEVi1EyXxqXoVaNmb R/cQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753976685; x=1754581485; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=8D6H3TovcRUpDHrrv443Wy2kKrliHPbwf72lIkroPTg=; b=kDfeO63j49cbPCFyR8fqCt6jS5Jtsz3mmsJep+CV7jitNM8i+FyYNYjoJuFIKKOt9R w8tQ7zFsuoHv2wgokIwc5IKM7nvu7FVkGbWlz2brtZkaQ/5YwPumkRGKscM8EjXxKzH+ E7jgCU59sZ44AVZWY73eG8hKAMloqzLQ8nT4ugKlZRe8VNyL3y8UK5Z1miP0LDsOW/LD ZjSNyzK6gUj/biFngxudD+V+9/GurLVzx4DVx6OdLLpn59osSLjX+OWkx1YfpwHdsLUP DhETiY4e5NhjEkbPvsYUrvI0lXFXHhzgIuqB6rEXlB1an7/gHBGbqHQn4tQyLZ+U3VUj YwVg== X-Forwarded-Encrypted: i=1; AJvYcCXrNBz296l2qqglLi71J71QQcW/koc4x9yFUJxI43IuLKPN6CjrTFM/IEa3DWfxmewheAY9Kdc=@vger.kernel.org X-Gm-Message-State: AOJu0YyXTeiKLlag+ayMwEHJVA/z3IsrLTNHcOP/6bcvwsw38ynr9hqg gfo+/oWOeEF0Rw5djhSGhuSGZoCuBlI7Ce9D4p7aiNzadkuMczdAvfZUt7OWO667uRT7CpEt+XT fOXZ0Hw== X-Google-Smtp-Source: AGHT+IG5srnDugZwbzwxdO5CMVzSLz47ALstUwtxD0ry/hJIfF+IqAvaHkQ39SziNPkrw/OnSv1Kvb0DGBw= X-Received: from pjbqd15.prod.google.com ([2002:a17:90b:3ccf:b0:314:d44:4108]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:562b:b0:312:959:dc4f with SMTP id 98e67ed59e1d1-31f5dd6b53amr9841464a91.5.1753976684978; Thu, 31 Jul 2025 08:44:44 -0700 (PDT) Date: Thu, 31 Jul 2025 08:44:41 -0700 Precedence: bulk X-Mailing-List: stable@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: <20250731154442.319568-1-surenb@google.com> Subject: [PATCH v2 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 --- Changes since v1 [1] - Fixed step size calculation, per Lokesh Gidra - Added missing check for UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES, per Lokesh Gidra [1] https://lore.kernel.org/all/20250730170733.3829267-1-surenb@google.com/ mm/userfaultfd.c | 45 +++++++++++++++++++++++++++++---------------- 1 file changed, 29 insertions(+), 16 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index cbed91b09640..b5af31c22731 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1818,28 +1818,41 @@ 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); + step_size = HPAGE_PMD_SIZE; + } else { spin_unlock(ptl); - split_huge_pmd(src_vma, src_pmd, src_addr); - /* The folio will be split by move_pages_pte() */ - continue; + if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { + err = -ENOENT; + break; + } + /* nothing to do to move a hole */ + err = 0; + step_size = min(HPAGE_PMD_SIZE, src_start + len - src_addr); } - - 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)) { if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { base-commit: 01da54f10fddf3b01c5a3b80f6b16bbad390c302 -- 2.50.1.552.g942d659e1b-goog