From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A6AE0C43381 for ; Tue, 26 Feb 2019 23:37:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E200218D0 for ; Tue, 26 Feb 2019 23:37:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="YIFxU2kk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729524AbfBZXhG (ORCPT ); Tue, 26 Feb 2019 18:37:06 -0500 Received: from mail-pf1-f193.google.com ([209.85.210.193]:36037 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729484AbfBZXg6 (ORCPT ); Tue, 26 Feb 2019 18:36:58 -0500 Received: by mail-pf1-f193.google.com with SMTP id n22so7018313pfa.3 for ; Tue, 26 Feb 2019 15:36:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=DEBVAMtax4OzUK5N+O2GdbAJZx0cc+8FrVNmyZKUAQc=; b=YIFxU2kk+jRTvhisTPnzHut//4afeoCxATSyPkc8NNLhJLTe0yFnnl3Fd+IT1OWjIk Md4KAzhJgsWSCNlWWNdjfOMB/dI8+ujGVrqFkgz2NkNcUXXqcmUcLgdwUxu34fCevC3w Wx+AfpwH1L9oN1Cp/ER/TuCElUWN8+UFN+iFU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=DEBVAMtax4OzUK5N+O2GdbAJZx0cc+8FrVNmyZKUAQc=; b=XRoYFWOQdUgN9jFD3Ug97pZCbTlUtriS3uQ+xtlNFHSVANzwTIwrptyzLrVUISvctg XMn8BZQYR1LWjvytekpZh3w5s2A71B8oAM0oQKojgDjAv5QphTK8RuOV5MuQ73qdsSev eE7Zr/aRnl+/CLo2wyadbly9F/Y/7GVdYScbnThSJrKmRQB9HDaOwp/0phVGkoctFG58 VdkdPKthTfODQw7H5Ou+Kbh1X77+soYz09sr9SRnwa8PViauxbvcz5k4atJwbs88axJ6 +mLDGV76Fnm1PR53XRn99E1ySMzHaEtj/L9lowi3liaycgo9mzmcpP31xrsrVkMbrS1o npFQ== X-Gm-Message-State: AHQUAuZpzGKe2jKi/3jvsNoW07WXeeMfZ2nKJ+VyiMFs6zSLEes0VNkw T1y73CpF/tbNE7wucXhbWy/ZEA== X-Google-Smtp-Source: AHgI3IbxyfGp4sLmEtEZZHKuN+ZqR8zfinoD6nbTKW6NtDqijg/YpLpTKahmS9w2vmf9CW2Rz3TCpA== X-Received: by 2002:a62:4641:: with SMTP id t62mr28291188pfa.141.1551224217647; Tue, 26 Feb 2019 15:36:57 -0800 (PST) Received: from www.outflux.net (173-164-112-133-Oregon.hfc.comcastbusiness.net. [173.164.112.133]) by smtp.gmail.com with ESMTPSA id h10sm488944pfo.128.2019.02.26.15.36.54 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 26 Feb 2019 15:36:54 -0800 (PST) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Peter Zijlstra , Jann Horn , Sean Christopherson , Dominik Brodowski , Kernel Hardening , linux-kernel@vger.kernel.org Subject: [PATCH 3/3] lkdtm: Check for SMEP clearing protections Date: Tue, 26 Feb 2019 15:36:47 -0800 Message-Id: <20190226233647.28547-4-keescook@chromium.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190226233647.28547-1-keescook@chromium.org> References: <20190226233647.28547-1-keescook@chromium.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This adds an x86-specific test for pinned cr4 bits. A successful test will validate pinning and check the ROP-style call-middle-of-function defense, if needed. For example, in the case of native_write_cr4() looking like this: ffffffff8171bce0 : ffffffff8171bce0: 48 8b 35 79 46 f2 00 mov 0xf24679(%rip),%rsi ffffffff8171bce7: 48 09 f7 or %rsi,%rdi ffffffff8171bcea: 0f 22 e7 mov %rdi,%cr4 ... ffffffff8171bd5a: c3 retq The UNSET_SMEP test will jump to ffffffff8171bcea (the mov to cr4) instead of ffffffff8171bce0 (native_write_cr4() entry) to simulate a direct-call bypass attempt. Expected successful results: # echo UNSET_SMEP > /sys/kernel/debug/provoke-crash/DIRECT # dmesg [ 79.594433] lkdtm: Performing direct entry UNSET_SMEP [ 79.596459] lkdtm: trying to clear SMEP normally [ 79.598406] lkdtm: ok: SMEP did not get cleared [ 79.599981] lkdtm: trying to clear SMEP with call gadget [ 79.601810] ------------[ cut here ]------------ [ 79.603421] Attempt to unpin cr4 bits: 100000; bypass attack?! ... [ 79.650170] ---[ end trace 2452ca0f6126242e ]--- [ 79.650937] lkdtm: ok: SMEP removal was reverted Signed-off-by: Kees Cook --- drivers/misc/lkdtm/bugs.c | 60 ++++++++++++++++++++++++++++++++++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + 3 files changed, 62 insertions(+) diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 7eebbdfbcacd..c79b43a5ba34 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -255,3 +255,63 @@ void lkdtm_STACK_GUARD_PAGE_TRAILING(void) pr_err("FAIL: accessed page after stack!\n"); } + +void lkdtm_UNSET_SMEP(void) +{ +#ifdef CONFIG_X86_64 + void (*direct_write_cr4)(unsigned long val); + unsigned char *insn; + unsigned long cr4; + int i; + + cr4 = native_read_cr4(); + + if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { + pr_err("FAIL: SMEP not in use\n"); + return; + } + cr4 &= ~(X86_CR4_SMEP); + + pr_info("trying to clear SMEP normally\n"); + native_write_cr4(cr4); + if (cr4 == native_read_cr4()) { + pr_err("FAIL: pinning SMEP failed!\n"); + cr4 |= X86_CR4_SMEP; + pr_info("restoring SMEP\n"); + native_write_cr4(cr4); + return; + } + pr_info("ok: SMEP did not get cleared\n"); + + /* + * To test the post-write pinning verification we need to call + * directly into the the middle of native_write_cr4() where the + * cr4 write happens, skipping the pinning. This searches for + * the cr4 writing instruction. + */ + insn = (unsigned char *)native_write_cr4; + for (i = 0; i < 64; i++) { + /* mov %rdi, %cr4 */ + if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) + break; + } + if (i >= 256) { + pr_info("ok: cannot locate cr4 writing call gadget\n"); + return; + } + direct_write_cr4 = (void *)(insn + i); + + pr_info("trying to clear SMEP with call gadget\n"); + direct_write_cr4(cr4); + if (native_read_cr4() & X86_CR4_SMEP) { + pr_info("ok: SMEP removal was reverted\n"); + } else { + pr_err("FAIL: cleared SMEP not detected!\n"); + cr4 |= X86_CR4_SMEP; + pr_info("restoring SMEP\n"); + native_write_cr4(cr4); + } +#else + pr_err("FAIL: this test is x86_64-only\n"); +#endif +} diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index 2837dc77478e..fd668776414b 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -132,6 +132,7 @@ static const struct crashtype crashtypes[] = { CRASHTYPE(CORRUPT_LIST_ADD), CRASHTYPE(CORRUPT_LIST_DEL), CRASHTYPE(CORRUPT_USER_DS), + CRASHTYPE(UNSET_SMEP), CRASHTYPE(CORRUPT_STACK), CRASHTYPE(CORRUPT_STACK_STRONG), CRASHTYPE(STACK_GUARD_PAGE_LEADING), diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h index 3c6fd327e166..9c78d7e21c13 100644 --- a/drivers/misc/lkdtm/lkdtm.h +++ b/drivers/misc/lkdtm/lkdtm.h @@ -26,6 +26,7 @@ void lkdtm_CORRUPT_LIST_DEL(void); void lkdtm_CORRUPT_USER_DS(void); void lkdtm_STACK_GUARD_PAGE_LEADING(void); void lkdtm_STACK_GUARD_PAGE_TRAILING(void); +void lkdtm_UNSET_SMEP(void); /* lkdtm_heap.c */ void lkdtm_OVERWRITE_ALLOCATION(void); -- 2.17.1