From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f54.google.com (mail-wr1-f54.google.com [209.85.221.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D95EF1A83F2 for ; Fri, 14 Feb 2025 23:06:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.54 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739574415; cv=none; b=GO1uAFmJwSgq/ipVYTTSx7gjOvBofJcqtD7IFL9d4CO5Sx94xCsw3FBacSEsGWtzXCWgSrXU6/Kn5wdvtY+93qFDlOnoos9/ZM041ynTHrXSXCMZ3g6oprjmgE15+vGXv5e3cGM0xnJiET4ZtDnjoMtq7a+nQJ2NP4UUhS+TCKU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739574415; c=relaxed/simple; bh=KyQL3L0qpc6BP+Wc2cClrEFXi5QBtwDn66b2cUtQHGI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fLf+4JAeq9jreWM0bx5XLZO1HJAjs4N98dZBK2aRxTDKHTSjXdFVaew8eZJvksc29Dote5i+tCSldOgoWBYSpJV1LxvrmfE1S32vLGzEXkPyZaOQU6RnXzpp9ytNx5zq9Yuq6q7j0qrpek2YKvj4l/AjcsQkkZ7XIaaSmC9l7Pw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=citrix.com; spf=pass smtp.mailfrom=cloud.com; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b=GOuUc9rR; arc=none smtp.client-ip=209.85.221.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=citrix.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=cloud.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="GOuUc9rR" Received: by mail-wr1-f54.google.com with SMTP id ffacd0b85a97d-38dd93a4e8eso2271583f8f.1 for ; Fri, 14 Feb 2025 15:06:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1739574412; x=1740179212; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to; bh=PB+r6JvVzie2JvMnY5R6Nkb8yUTw2Iu5MRXRiO5OIrs=; b=GOuUc9rRT02Q4U23i5kui/A2Bmjf6IcdJ+UIJc98pgRgVeEGOQuoURAvkxdF9Yx6rD mwUaZOwVs0G1SeoV+7u9i7i3ymmr670xx/ilYbq/2h28jcsknLpm07iy605tk3I9VO1p 4n0ilTUgiP+38IcixEmuuHlhW+bcnCD0+MEZ8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739574412; x=1740179212; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=PB+r6JvVzie2JvMnY5R6Nkb8yUTw2Iu5MRXRiO5OIrs=; b=CKsCN9NN4jKV7Em4XjqmtOB7oMnX2ppQP/KraX7KJAkV0CsFS4kVG9lNUrT7/DOSPP keM1nwYtZPlTqDeu2m4J8P+kRGfzTYYMumt+4YMC3OlpCtdE1NW/XAVF900ToCxh20Y7 y+RaXxEFN+vMDO22rCE+8E5/wQ4kEYfaLgFk0VXid/DAa/cIqdmvk7tEgbsZm9ApEVc9 SJ4ws3a0aLYHh77QmRshjaA8Wusn/geSKF8k64xbegYyAfjYaUoP2RkSC9EGBnbBwMth Gb8UHUekRr8b61EaC3ShRMktlKzgRdt9JIpFdhv1rDmKzXxTnfRiQ3pHon6Pwr5UppCE AY+g== X-Forwarded-Encrypted: i=1; AJvYcCXzPr+FTITJuoFj4o5diuUiD+G94QzfxGdyYtUmILrzTUF/736E5ut3oUG/LSq04MVbeBRh3QxP6tiQiig=@vger.kernel.org X-Gm-Message-State: AOJu0YxyviopxR74fs4QgIyFjY7ywT0Fs5H6Ke3V6PYpLP0z6+JMr8Xk hGzV6fFRbI4vUcP/7pdpy6/Co5o9iP5B/cKvsVpjILZcnPaNudXl9TV7X6BrwFk= X-Gm-Gg: ASbGncvDQLzOaVYCmzKKuZyXj3N4OzrUGiuuWD9bgdRNyEPu3x94F43qd/LWAGTTk9Z i72dYa6FzUeJk2h5njX5pYa3kt/DJKeTBkSRbA4eomAUUBxziTdUABMPe2bCDJpsPThojln6sK+ 1X17VP1LAK5/pml7tJZFRttWO3tblCqFu2ua9XIeN5CjfbOin1L4R5FJZ9ovXLHtF7jpSMwOnuB 8TJkQLDdXQlQByNjWuofF/C4lbwjGu+jORXeDBHl+eJgaoikGIE7GXC6LTtE/omsdfvn+Yt16jx qsYi/YdBP6JA8w19EGqKS3KnKRdE7MAx2AjaA8y66bcF5D+oymJkXrs= X-Google-Smtp-Source: AGHT+IFLQd2UoaUoR8vSrVkmfa1fsW1c99PulW/ZI1I/6rPcmxTRozmB9oTxgdVe8prRiiraCjwMUg== X-Received: by 2002:adf:fa08:0:b0:38f:2a99:b377 with SMTP id ffacd0b85a97d-38f33f57459mr1030799f8f.53.1739574412141; Fri, 14 Feb 2025 15:06:52 -0800 (PST) Received: from [192.168.1.10] (host-92-26-98-202.as13285.net. [92.26.98.202]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259d5923sm5795765f8f.74.2025.02.14.15.06.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Feb 2025 15:06:51 -0800 (PST) Message-ID: Date: Fri, 14 Feb 2025 23:06:50 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] Circumventing FineIBT Via Entrypoints To: Jennifer Miller , Jann Horn Cc: Andy Lutomirski , linux-hardening@vger.kernel.org, kees@kernel.org, joao@overdrivepizza.com, samitolvanen@google.com, kernel list References: <60447cd2-a8da-4be6-80fa-a5639b7455b1@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 13/02/2025 11:24 pm, Jennifer Miller wrote: > On Thu, Feb 13, 2025 at 09:24:18PM +0000, Andrew Cooper wrote: >>>> ; swap stacks as normal >>>> mov QWORD PTR gs:[rip+0x7f005f85],rsp # 0x6014 >>>> mov rsp,QWORD PTR gs:[rip+0x7f02c56d] # 0x2c618 >> ... these are memory accesses using the user %gs.  As you note a few >> lines lower, %gs isn't safe at this point. >> >> A cunning attacker can make gs:[rip+0x7f02c56d] be a read-only mapping, >> at point we'll have loaded an attacker controlled %rsp, then take #PF >> trying to spill %rsp into pcpu_hot, and now we're running the pagefault >> handler on an attacker controlled stack and gsbase. >> > I don't follow, the spill of %rsp into pcpu_hot occurs first, before we > would move to the attacker controlled stack. This is Intel asm syntax, > sorry if that was unclear. No, sorry.  It's clearly written; I simply wasn't paying enough attention. > Still, I hadn't considered misusing readonly/unmapped pages on the GPR > register spill that follows. Could we enforce that the stack pointer we get > be page aligned to prevent this vector? So that if one were to attempt to > point the stack to readonly or unmapped memory they should be guaranteed to > double fault? Hmm. Espfix64 does involve #DF recovering from a write to a read-only stack.  (This broken corner of x86 is also fixed in FRED.   We fixed a *lot* of thing.) As long the #DF handler can be updated to safely distinguish espfix64 from this entrypoint attack, this seems like it might mitigate the read-only case. > I think we can do the overwrite at any point before actually calling into > the individual syscall handlers, really anywhere before potentially > hijacked indirect control flow can occur and then restore it just after > those return e.g., for the 64-bit path I am currently overwriting it at the > start of do_syscall_64 and then restoring it just before > syscall_exit_to_user_mode. I'm not sure if there is any reason to do it > sooner while we'd still be register constrained. I don't follow.  If any "bad" execution is found in an entrypoint, Linux needs to panic().  Detecting the malice involves clobbering an in-use stack, and there's no ability to safely recover. ~Andrew