From nobody Mon Feb 9 00:31:16 2026 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.21]) (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 8E29114A0BE for ; Thu, 15 Feb 2024 23:14:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.21 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708038885; cv=none; b=cb045/qJ6zu+wrCr5cVaqHLljkROJ3BpUoiQVVERDX0FdDWTGBgGvgpr3UFyHpG6sLTsAjDXbOmx5Zq3pKAEKfL7qAc6zGyUAToruQ1WvBfDs7mCcrI4A0vAT/jg+pUwhXa59j2fyht1DS8Dez6nFH3aFP2e8ataRZKgulPAw1Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708038885; c=relaxed/simple; bh=Ib9DRZGDBCSUD4uXPmR+ijcvzy4h1J3AkaOgyP6jQrA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=QlhR5j7cZdmVHU4nxOXRX4SH6QHfiYuRku/AmVqCvQXhUMzFA7LVUp4t/UrziUvFp+0xmLCPns7BIabNk5Hqa75l0ml6cwK6ekmJEP7EjofApmj1DW+rdHTgOayN+JcawQfQPwbssya6+MymRPiYdIXi7FHcTArrgsHNbJrzjNg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=aZFz9HTh; arc=none smtp.client-ip=198.175.65.21 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="aZFz9HTh" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1708038884; x=1739574884; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=Ib9DRZGDBCSUD4uXPmR+ijcvzy4h1J3AkaOgyP6jQrA=; b=aZFz9HThrAXYgiC93qZAMnKdqWEZXqXnbLivzJoGt6MORRK3hWMLXBBb mdYwToFGS83l+1BJsVIb1vz7QYsW3lqm8vbPZ6MbvPlG2AsNv347Kh4fz 86l86S03256YyZBJU7Ae7P4sgVea75b2YLRXQe/oZ3XhNurn2N6sn1qIu nYruggcY+Gz5748T/jpXg259Ve5H1kY1mSws/MWV3CNNTuWf/epzFI1FD /U5FB73nXTBvk6/FHRovQ1R71jyXJywfnbGLhoCwSWplc/LhXmO42VE+w Eb/f43bAYS1zhnoPOp95vhZtUiZMBpmP1ioK73ngqHKh2EpfOYBl05jHx A==; X-IronPort-AV: E=McAfee;i="6600,9927,10985"; a="2066367" X-IronPort-AV: E=Sophos;i="6.06,162,1705392000"; d="scan'208";a="2066367" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orvoesa113.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Feb 2024 15:14:41 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10985"; a="912250200" X-IronPort-AV: E=Sophos;i="6.06,162,1705392000"; d="scan'208";a="912250200" Received: from yshin-mobl1.amr.corp.intel.com (HELO rpedgeco-desk4.intel.com) ([10.209.95.133]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Feb 2024 15:14:40 -0800 From: Rick Edgecombe To: Liam.Howlett@oracle.com, akpm@linux-foundation.org, debug@rivosinc.com, broonie@kernel.org, kirill.shutemov@linux.intel.com, keescook@chromium.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, luto@kernel.org, peterz@infradead.org, hpa@zytor.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: rick.p.edgecombe@intel.com Subject: [RFC PATCH 5/8] mm: Take placement mappings gap into account Date: Thu, 15 Feb 2024 15:13:29 -0800 Message-Id: <20240215231332.1556787-6-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240215231332.1556787-1-rick.p.edgecombe@intel.com> References: <20240215231332.1556787-1-rick.p.edgecombe@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable When memory is being placed, mmap() will take care to respect the guard gaps of certain types of memory (VM_SHADOWSTACK, VM_GROWSUP and VM_GROWSDOWN). In order to ensure guard gaps between mappings, mmap() needs to consider two things: 1. That the new mapping isn=E2=80=99t placed in an any existing mappings g= uard gaps. 2. That the new mapping isn=E2=80=99t placed such that any existing mappin= gs are not in *its* guard gaps. The long standing behavior of mmap() is to ensure 1, but not take any care around 2. So for example, if there is a PAGE_SIZE free area, and a mmap() with a PAGE_SIZE size, and a type that has a guard gap is being placed, mmap() may place the shadow stack in the PAGE_SIZE free area. Then the mapping that is supposed to have a guard gap will not have a gap to the adjacent VMA. For MAP_GROWSDOWN/VM_GROWSDOWN and MAP_GROWSUP/VM_GROWSUP this has not been a problem in practice because applications place these kinds of mappings very early, when there is not many mappings to find a space between. But for shadow stacks, they may be placed throughout the lifetime of the application. So define a VM_UNMAPPED_START_GAP_SET flag to specify that a start_gap field has been set, as most vm_unmapped_area_info structs are not zeroed, so the added field will often contain garbage. Use VM_UNMAPPED_START_GAP_SET in unmapped_area/_topdown() to find a space that includes the guard gap for the new mapping. Take care to not interfere with the alignment. Signed-off-by: Rick Edgecombe --- include/linux/mm.h | 2 ++ mm/mmap.c | 21 ++++++++++++++------- 2 files changed, 16 insertions(+), 7 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 9addf16dbf18..160bb6db7a16 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3393,12 +3393,14 @@ extern unsigned long __must_check vm_mmap(struct fi= le *, unsigned long, =20 struct vm_unmapped_area_info { #define VM_UNMAPPED_AREA_TOPDOWN 1 +#define VM_UNMAPPED_START_GAP_SET 2 unsigned long flags; unsigned long length; unsigned long low_limit; unsigned long high_limit; unsigned long align_mask; unsigned long align_offset; + unsigned long start_gap; }; =20 extern unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info); diff --git a/mm/mmap.c b/mm/mmap.c index 936d728ba1ca..1b6c333656f9 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1567,14 +1567,17 @@ static inline int accountable_mapping(struct file *= file, vm_flags_t vm_flags) */ static unsigned long unmapped_area(struct vm_unmapped_area_info *info) { - unsigned long length, gap; + unsigned long length, gap, start_gap =3D 0; unsigned long low_limit, high_limit; struct vm_area_struct *tmp; =20 MA_STATE(mas, ¤t->mm->mm_mt, 0, 0); =20 + if (info->flags & VM_UNMAPPED_START_GAP_SET) + start_gap =3D info->start_gap; + /* Adjust search length to account for worst case alignment overhead */ - length =3D info->length + info->align_mask; + length =3D info->length + info->align_mask + start_gap; if (length < info->length) return -ENOMEM; =20 @@ -1586,7 +1589,7 @@ static unsigned long unmapped_area(struct vm_unmapped= _area_info *info) if (mas_empty_area(&mas, low_limit, high_limit - 1, length)) return -ENOMEM; =20 - gap =3D mas.index; + gap =3D mas.index + start_gap; gap +=3D (info->align_offset - gap) & info->align_mask; tmp =3D mas_next(&mas, ULONG_MAX); if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if = possible */ @@ -1619,13 +1622,17 @@ static unsigned long unmapped_area(struct vm_unmapp= ed_area_info *info) */ static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *i= nfo) { - unsigned long length, gap, gap_end; + unsigned long length, gap, gap_end, start_gap =3D 0; unsigned long low_limit, high_limit; struct vm_area_struct *tmp; =20 MA_STATE(mas, ¤t->mm->mm_mt, 0, 0); + + if (info->flags & VM_UNMAPPED_START_GAP_SET) + start_gap =3D info->start_gap; + /* Adjust search length to account for worst case alignment overhead */ - length =3D info->length + info->align_mask; + length =3D info->length + info->align_mask + start_gap; if (length < info->length) return -ENOMEM; =20 @@ -1832,7 +1839,7 @@ unsigned long mm_get_unmapped_area_vmflags(struct mm_= struct *mm, struct file *fi =20 unsigned long __get_unmapped_area(struct file *file, unsigned long addr, unsigned long l= en, - unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags) + unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags) { unsigned long (*get_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long) @@ -1883,7 +1890,7 @@ __get_unmapped_area(struct file *file, unsigned long = addr, unsigned long len, =20 unsigned long get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, - unsigned long pgoff, unsigned long flags) + unsigned long pgoff, unsigned long flags) { return __get_unmapped_area(file, addr, len, pgoff, flags, 0); } --=20 2.34.1