From nobody Tue Feb 10 16:22:20 2026 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 AD637EB64DA for ; Tue, 4 Jul 2023 15:37:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231828AbjGDPhX (ORCPT ); Tue, 4 Jul 2023 11:37:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231750AbjGDPhP (ORCPT ); Tue, 4 Jul 2023 11:37:15 -0400 Received: from mail-wr1-x433.google.com (mail-wr1-x433.google.com [IPv6:2a00:1450:4864:20::433]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6031BE42 for ; Tue, 4 Jul 2023 08:37:14 -0700 (PDT) Received: by mail-wr1-x433.google.com with SMTP id ffacd0b85a97d-307d20548adso6353240f8f.0 for ; Tue, 04 Jul 2023 08:37:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1688485032; x=1691077032; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=R7tunI1lKMH4tXxhhZlNnHm4rteRjjg9hHxMHKz9rMs=; b=IH8/lYadcMH//iw9M9Op8dU0l1sj9aFWw0lBe6q6pMiopghB2cvLo/OcIkjbXfOgC6 Y7x5+a5kcNvS9pp+WWGqp5o36R5bI4rsQwvbYsUc1Qx6T4i713ReMLLt4ZaDVZsYaSd5 A3rBFK/cCnkuHUUrd8RED5SGzIm8RjYv50e0Y= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688485032; x=1691077032; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=R7tunI1lKMH4tXxhhZlNnHm4rteRjjg9hHxMHKz9rMs=; b=YAJu9BjjfN8+TYd0Nt1Lp57Ikw7WDZGHqjRCYNtEScSb6Qjj8aZNy1t6b8kUtHG1TV rCz/4heUAb+GZmuur/RIr+limqkce2IJxrtUv6eBZ1gXT/kYSOXEUtdgDXsvNs2DCx6L Ml7uPZxHNcYZjNPXeBWh7qpAqSzeO7J83mxfO0u12ZLUnc6VGj6hn3aEZqL/XnzYpygF HHTEkTGE6gq4C+69vRUsYBOtZ+7vg120cTmwkkU/AtBFcI9LRikgW9fYHoG+ix4tM+0q NPVPnYJUWtbpfyFB27w+uX7KZvbFVpd3gKNF8f3xs4J1Czvw8K1dwcqdo/+l9DEDv0J3 cOnw== X-Gm-Message-State: ABy/qLZRFdQIjVjwyk4k2bYnmt8rncUUGbFjOsZr+8c4ZZzqXTkYF1+x 3EpqAeGx6lukjvHAJyhI81cnS8FMZuwNtr3krGc= X-Google-Smtp-Source: APBJJlEk398zYlZ/TviSclnfJx8pfvjJ6ut2plYZwXPVcNfINX4lPmJVH71We1oWGxYpyyxB1gS6eg== X-Received: by 2002:a5d:4f86:0:b0:30f:c42e:3299 with SMTP id d6-20020a5d4f86000000b0030fc42e3299mr10482799wru.60.1688485032503; Tue, 04 Jul 2023 08:37:12 -0700 (PDT) Received: from revest.zrh.corp.google.com ([2a00:79e0:9d:6:99b2:81bb:8407:5369]) by smtp.gmail.com with ESMTPSA id b2-20020adfde02000000b0030c4d8930b1sm28538709wrm.91.2023.07.04.08.37.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Jul 2023 08:37:11 -0700 (PDT) From: Florent Revest To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, anshuman.khandual@arm.com, joey.gouly@arm.com, mhocko@suse.com, keescook@chromium.org, 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, Florent Revest Subject: [PATCH v3 4/5] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl Date: Tue, 4 Jul 2023 17:36:28 +0200 Message-ID: <20230704153630.1591122-5-revest@chromium.org> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog In-Reply-To: <20230704153630.1591122-1-revest@chromium.org> References: <20230704153630.1591122-1-revest@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 Reviewed-by: Catalin Marinas Reviewed-by: Kees Cook --- 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) =20 #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 &=3D ~((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) =20 #define PR_GET_MDWE 66 =20 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); =20 if (current->mm) { - mm->flags =3D current->mm->flags & MMF_INIT_MASK; + mm->flags =3D mmf_init_flags(current->mm->flags); mm->def_flags =3D current->mm->def_flags & VM_INIT_DEF_MASK; } else { mm->flags =3D 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, unsigne= d long start, } #endif /* CONFIG_ANON_VMA_NAME */ =20 +static inline unsigned long get_current_mdwe(void) +{ + unsigned long ret =3D 0; + + if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) + ret |=3D PR_MDWE_REFUSE_EXEC_GAIN; + if (test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags)) + ret |=3D 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; =20 - 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; =20 + current_bits =3D get_current_mdwe(); + if (current_bits && current_bits !=3D bits) + return -EPERM; /* Cannot unset the flags */ + + 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 */ =20 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(); } =20 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/pr= ctl.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) =20 #define PR_GET_MDWE 66 =20 --=20 2.41.0.255.g8b1d071c50-goog