From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55701C83F01 for ; Fri, 25 Aug 2023 22:39:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230256AbjHYWi4 (ORCPT ); Fri, 25 Aug 2023 18:38:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47068 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230221AbjHYWil (ORCPT ); Fri, 25 Aug 2023 18:38:41 -0400 Received: from mail-pf1-x434.google.com (mail-pf1-x434.google.com [IPv6:2607:f8b0:4864:20::434]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4C71D269F for ; Fri, 25 Aug 2023 15:38:38 -0700 (PDT) Received: by mail-pf1-x434.google.com with SMTP id d2e1a72fcca58-68a3e943762so1260442b3a.1 for ; Fri, 25 Aug 2023 15:38:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1693003118; x=1693607918; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=pvT61EgqHV2sXzVGpzHb3/Do1J2IZRGpt5oeUSTXS1M=; b=DOo8GPav/4/T0YBMMrO/cePh0ds1j+7XmPnsFiA81vr3N7hBMYIs6zg16ettL7gDXz p9nCAjfggAkvTQaYkLHvydpFAuhhirXtq//ddTQNDrBzPaMlhwBaL0SlAH2fNVt/COZa OKKoiWuxLo6XsHLH8vlgCysrsRSCMT9yGkNIc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693003118; x=1693607918; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=pvT61EgqHV2sXzVGpzHb3/Do1J2IZRGpt5oeUSTXS1M=; b=Lc+BvoLRt8m8IbtBAR5eJ1zyqTC+C7HqBXiRdMN7a7/i2v8biqUl92soNJrfBaFCxt ozkfI/OPGzHtvn07q38JIDANxo9Tq6wtmGs/tL2zl37w5jyzjQyzK/aHjf86vtVdK4yO QFp1wl8TxBerk8B3KF5myf3vH2L3/dZIW1ouGCKtoRtZTzZgMtsJFjEwcINyJ7bPujqD kLqBFjXpdh49MQ700omsj9+zdA5liocpBYIPmXkVkFCleiVSoEJDDeOYefXy9S8dU34e L2vaSJSas61vZistDXqMhrjco6PksX+S7Sx+WtNi1RU9dRor2Tz2b3ejeP5ZKnVsBOUu ZHuQ== X-Gm-Message-State: AOJu0YyIqUE/g3Uc+tdL1JZD301pjCKUNLM2wOpU1+Xvtwmd6wh85oDj yONrPuw7BzXMt8OHne0WuOo8oA== X-Google-Smtp-Source: AGHT+IHtcM7TBjRhEYZWBp/1bp8NSpQ8O6IsMGa1gTP1wB419PgWbxNHloZgf1ds3UA3SEXCGogzLg== X-Received: by 2002:a05:6a20:258b:b0:13e:1945:8873 with SMTP id k11-20020a056a20258b00b0013e19458873mr23803455pzd.37.1693003117713; Fri, 25 Aug 2023 15:38:37 -0700 (PDT) Received: from www.outflux.net (198-0-35-241-static.hfc.comcastbusiness.net. [198.0.35.241]) by smtp.gmail.com with ESMTPSA id a3-20020aa78643000000b0068874e1faf2sm2069987pfo.56.2023.08.25.15.38.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Aug 2023 15:38:36 -0700 (PDT) Date: Fri, 25 Aug 2023 15:38:36 -0700 From: Kees Cook To: Florent Revest Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, catalin.marinas@arm.com, anshuman.khandual@arm.com, joey.gouly@arm.com, mhocko@suse.com, david@redhat.com, peterx@redhat.com, izbyshev@ispras.ru, broonie@kernel.org, szabolcs.nagy@arm.com, kpsingh@kernel.org, gthelen@google.com, toiwoton@gmail.com Subject: Re: [PATCH v3 4/5] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl Message-ID: <202308251535.551E797B1@keescook> References: <20230704153630.1591122-1-revest@chromium.org> <20230704153630.1591122-5-revest@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230704153630.1591122-5-revest@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 04, 2023 at 05:36:28PM +0200, Florent Revest wrote: > This extends the current PR_SET_MDWE prctl arg with a bit to indicate > that the process doesn't want MDWE protection to propagate to children. > > To implement this no-inherit mode, the tag in current->mm->flags must be > absent from MMF_INIT_MASK. This means that the encoding for "MDWE but > without inherit" is different in the prctl than in the mm flags. This > leads to a bit of bit-mangling in the prctl implementation. > > Signed-off-by: Florent Revest > --- > include/linux/sched/coredump.h | 10 ++++++++++ > include/uapi/linux/prctl.h | 1 + > kernel/fork.c | 2 +- > kernel/sys.c | 32 ++++++++++++++++++++++++++------ > tools/include/uapi/linux/prctl.h | 1 + > 5 files changed, 39 insertions(+), 7 deletions(-) > > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index 0ee96ea7a0e9..1b37fa8fc723 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -91,4 +91,14 @@ static inline int get_dumpable(struct mm_struct *mm) > MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK) > > #define MMF_VM_MERGE_ANY 29 > +#define MMF_HAS_MDWE_NO_INHERIT 30 > + > +static inline unsigned long mmf_init_flags(unsigned long flags) > +{ > + if (flags & (1UL << MMF_HAS_MDWE_NO_INHERIT)) > + flags &= ~((1UL << MMF_HAS_MDWE) | > + (1UL << MMF_HAS_MDWE_NO_INHERIT)); > + return flags & MMF_INIT_MASK; > +} > + > #endif /* _LINUX_SCHED_COREDUMP_H */ > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index 6e9af6cbc950..dacbe824e7c3 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -284,6 +284,7 @@ struct prctl_mm_map { > /* Memory deny write / execute */ > #define PR_SET_MDWE 65 > # define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0) > +# define PR_MDWE_NO_INHERIT (1UL << 1) > > #define PR_GET_MDWE 66 > > diff --git a/kernel/fork.c b/kernel/fork.c > index d17995934eb4..bc3c762d378f 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1284,7 +1284,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, > hugetlb_count_init(mm); > > if (current->mm) { > - mm->flags = current->mm->flags & MMF_INIT_MASK; > + mm->flags = mmf_init_flags(current->mm->flags); > mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK; > } else { > mm->flags = default_dump_filter; > diff --git a/kernel/sys.c b/kernel/sys.c > index 339fee3eff6a..1a2dc3da43ea 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2362,19 +2362,41 @@ static int prctl_set_vma(unsigned long opt, unsigned long start, > } > #endif /* CONFIG_ANON_VMA_NAME */ > > +static inline unsigned long get_current_mdwe(void) > +{ > + unsigned long ret = 0; > + > + if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) > + ret |= PR_MDWE_REFUSE_EXEC_GAIN; > + if (test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags)) > + ret |= PR_MDWE_NO_INHERIT; > + > + return ret; > +} > + > static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3, > unsigned long arg4, unsigned long arg5) > { > + unsigned long current_bits; > + > if (arg3 || arg4 || arg5) > return -EINVAL; > > - if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN)) > + if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT)) > + return -EINVAL; > + > + /* NO_INHERIT only makes sense with REFUSE_EXEC_GAIN */ > + if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN)) > return -EINVAL; > > + current_bits = get_current_mdwe(); > + if (current_bits && current_bits != bits) > + return -EPERM; /* Cannot unset the flags */ I was pondering why PR_MDWE_NO_INHERIT can't be unset, but I guess it doesn't matter. Anything forked with have it off, and any process wanting to launch stuff before locking down can just skip running the prctl() until later. > + > + if (bits & PR_MDWE_NO_INHERIT) > + set_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags); > if (bits & PR_MDWE_REFUSE_EXEC_GAIN) > set_bit(MMF_HAS_MDWE, ¤t->mm->flags); > - else if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) > - return -EPERM; /* Cannot unset the flag */ > > return 0; > } > @@ -2384,9 +2406,7 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3, > { > if (arg2 || arg3 || arg4 || arg5) > return -EINVAL; > - > - return test_bit(MMF_HAS_MDWE, ¤t->mm->flags) ? > - PR_MDWE_REFUSE_EXEC_GAIN : 0; > + return (int)get_current_mdwe(); > } > > static int prctl_get_auxv(void __user *addr, unsigned long len) > diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h > index 6e9af6cbc950..dacbe824e7c3 100644 > --- a/tools/include/uapi/linux/prctl.h > +++ b/tools/include/uapi/linux/prctl.h > @@ -284,6 +284,7 @@ struct prctl_mm_map { > /* Memory deny write / execute */ > #define PR_SET_MDWE 65 > # define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0) > +# define PR_MDWE_NO_INHERIT (1UL << 1) > > #define PR_GET_MDWE 66 > > -- > 2.41.0.255.g8b1d071c50-goog > Reviewed-by: Kees Cook -- Kees Cook