From nobody Sun Feb 8 21:46:39 2026 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.12]) (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 1C32C131E3C for ; Mon, 26 Feb 2024 19:10:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.12 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708974604; cv=none; b=CA5SIDSE8QVMHQ/cEpGGm1kJdiV/+gKalx/ryv3Z6ETpq/ssyiMU24xfcPZAbvoYGdxLm82yM6ydff5aBBpesA2aEmtuygXH4dSjDrCzPYYy+PD7X5gj3MB+hWiLW3ABn+nevVW9zZ1lp6L92uYlGVssElu6szwucPsdB7he+Bs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708974604; c=relaxed/simple; bh=U3F9hHxdfZ7A6mCry7GoiZtnuJCP/wXQbUGWHcLnyx0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=kF9ODpnBxB+lQljNPn29vva66zZBvKBlYf2hBEK0HZEzbaaP+x2UhF09SfK9vSj3pxRkJZvb32B4sM+OYgBbMj0/X3CzG0buVkXH2tNPmksfsWEppjMrH0QKAqYjRDFCaRqCZM/9TkOeSrlpG6sf5rGqYdKCOnmguCa/z0dkLoQ= 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=jZr3WyDE; arc=none smtp.client-ip=198.175.65.12 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="jZr3WyDE" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1708974603; x=1740510603; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=U3F9hHxdfZ7A6mCry7GoiZtnuJCP/wXQbUGWHcLnyx0=; b=jZr3WyDERrAyY/xBfwcsOm7udIKEXcLZQIXVvXpkOb+fXQ2tduZ8yLCP Jy/l5vfDm5tHia8AOgqu/Dwn9paTGvM/51ToDFboZEizHA/XFCTAdOj41 IMZzZLWSH2kvJ540UgkQOmcjcgOcfE5mp2NFbF/NUZVyH5TZi7UuXHRO1 3Ih8A04OF8r/Nb/wUeTRr796EUUL2KYxWEtJQ66i3urYTEuMh3JrXSGLJ wT8IxCTuNyS7Is+tdgRFKpjb16edsm7+wXPiDU1rbvY0gWvm1w2SdG+4t Dd+Tl1aR5jqQyhUcaZpAVPpI+WPactiXygL7fC8fBphG0JA7Ba1VWcesj w==; X-IronPort-AV: E=McAfee;i="6600,9927,10996"; a="14721395" X-IronPort-AV: E=Sophos;i="6.06,186,1705392000"; d="scan'208";a="14721395" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Feb 2024 11:10:03 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,186,1705392000"; d="scan'208";a="6911463" Received: from bdmirand-mobl.amr.corp.intel.com (HELO rpedgeco-desk4.intel.com) ([10.251.3.213]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Feb 2024 11:10:02 -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: [PATCH v2 6/9] mm: Take placement mappings gap into account Date: Mon, 26 Feb 2024 11:09:48 -0800 Message-Id: <20240226190951.3240433-7-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240226190951.3240433-1-rick.p.edgecombe@intel.com> References: <20240226190951.3240433-1-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. Use the start_gap field 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 --- v2: - Remove VM_UNMAPPED_START_GAP_SET and have struct vm_unmapped_area_info initialized with zeros (in another patch). (Kirill) - Drop unrelated space change (Kirill) - Add comment around interactions of alignment and start gap step (Kirill) --- include/linux/mm.h | 1 + mm/mmap.c | 12 +++++++++--- 2 files changed, 10 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index a091181ef65a..19fc1eb86b9a 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3406,6 +3406,7 @@ struct vm_unmapped_area_info { 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 33af683a643f..3d7642eb84ea 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1574,7 +1574,7 @@ static unsigned long unmapped_area(struct vm_unmapped= _area_info *info) MA_STATE(mas, ¤t->mm->mm_mt, 0, 0); =20 /* Adjust search length to account for worst case alignment overhead */ - length =3D info->length + info->align_mask; + length =3D info->length + info->align_mask + info->start_gap; if (length < info->length) return -ENOMEM; =20 @@ -1586,7 +1586,13 @@ static unsigned long unmapped_area(struct vm_unmappe= d_area_info *info) if (mas_empty_area(&mas, low_limit, high_limit - 1, length)) return -ENOMEM; =20 - gap =3D mas.index; + /* + * Adjust for the gap first so it doesn't interfere with the + * later alignment. The first step is the minimum needed to + * fufill the start gap, the next steps is the minimum to align + * that. It is the minimum needed to fufill both. + */ + gap =3D mas.index + info->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 */ @@ -1625,7 +1631,7 @@ static unsigned long unmapped_area_topdown(struct vm_= unmapped_area_info *info) =20 MA_STATE(mas, ¤t->mm->mm_mt, 0, 0); /* Adjust search length to account for worst case alignment overhead */ - length =3D info->length + info->align_mask; + length =3D info->length + info->align_mask + info->start_gap; if (length < info->length) return -ENOMEM; =20 --=20 2.34.1