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[198.145.29.99]) by mx.google.com with ESMTPS id o39si6470031pje.28.2019.06.29.16.43.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 29 Jun 2019 16:43:31 -0700 (PDT) Received-SPF: pass (google.com: domain of luto@kernel.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=ItDaQR+Y; spf=pass (google.com: domain of luto@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=luto@kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from mail-wr1-f47.google.com (mail-wr1-f47.google.com [209.85.221.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 99C13217D7 for ; Sat, 29 Jun 2019 23:43:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561851810; bh=6Ls1mmfTCbzFx4Rzb3UhYmFEV6me19aFFOMlTGuTuMY=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=ItDaQR+YFwM+zUWyq0SEZyW3Pn6dapJHuivHM4jw8jYIYATlvNCFgUOVSyHA15NNw AEZK10pv6CFtIGXjIbUG7AXyDMsOmLHnHbBJ/EnoIw6y8yuhITck+ydss7eXTQlmm2 HPBufIxfXjHuzQKQSM+5jkAcCFZ77DOpPDDnzdOY= Received: by mail-wr1-f47.google.com with SMTP id x4so9909379wrt.6 for ; Sat, 29 Jun 2019 16:43:30 -0700 (PDT) X-Received: by 2002:adf:dd0f:: with SMTP id a15mr10561378wrm.265.1561851809106; Sat, 29 Jun 2019 16:43:29 -0700 (PDT) MIME-Version: 1.0 References: <20190628194158.2431-1-yu-cheng.yu@intel.com> <20190628194158.2431-2-yu-cheng.yu@intel.com> In-Reply-To: <20190628194158.2431-2-yu-cheng.yu@intel.com> From: Andy Lutomirski Date: Sat, 29 Jun 2019 16:43:18 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 2/3] Introduce arch_prctl(ARCH_X86_CET_MARK_LEGACY_CODE) To: Yu-cheng Yu Cc: X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , "open list:DOCUMENTATION" , Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Jun 28, 2019, at 12:41 PM, Yu-cheng Yu wrote: > > The CET legacy code bitmap covers the whole user-mode address space and i= s > located at the top of the user-mode address space. It is allocated only > when the first time arch_prctl(ARCH_X86_MARK_LEGACY_CODE) is called from > an application. > > Introduce: > > arch_prctl(ARCH_X86_MARK_LEGACY_CODE, unsigned long *buf) > Mark an address range as IBT legacy code. How about defining a struct for this? The change log should discuss where the bitmap goes and how it=E2=80=99s al= located. > +static int alloc_bitmap(void) > +{ > + unsigned long addr; > + u64 msr_ia32_u_cet; > + > + addr =3D do_mmap_locked(NULL, IBT_BITMAP_ADDR, IBT_BITMAP_SIZE, > + PROT_READ | PROT_WRITE, > + MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, > + VM_IBT | VM_NORESERVE, NULL); > + > + if (IS_ERR((void *)addr)) > + return addr; > + > + current->thread.cet.ibt_bitmap_addr =3D addr; addr is a constant. Why are you storing it? If it ends up not being constant, you should wire up mremap like the vDSO does. > +static int set_user_bits(unsigned long __user *buf, unsigned long buf_si= ze, > + unsigned long start_bit, unsigned long end_bit, unsigned lo= ng set) > +{ > + unsigned long start_ul, end_ul, total_ul; > + int i, j, r; > + > + if (round_up(end_bit, BITS_PER_BYTE) / BITS_PER_BYTE > buf_size) > + end_bit =3D buf_size * BITS_PER_BYTE - 1; > + > + start_ul =3D start_bit / BITS_PER_LONG; > + end_ul =3D end_bit / BITS_PER_LONG; > + total_ul =3D (end_ul - start_ul + 1); > + > + i =3D start_bit % BITS_PER_LONG; > + j =3D end_bit % BITS_PER_LONG; > + > + r =3D 0; > + put_user_try { put_user_try is obsolete. Just use get_user(), etc. Also, I must be missing something fundamental, because this series claims that user code can't write directly to the bitmap. This means that this entire function shouldn't work at all.