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=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS 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 D8330C43381 for ; Wed, 6 Mar 2019 09:56:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B4A68206DD for ; Wed, 6 Mar 2019 09:56:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729945AbfCFJ45 (ORCPT ); Wed, 6 Mar 2019 04:56:57 -0500 Received: from terminus.zytor.com ([198.137.202.136]:41673 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726596AbfCFJ44 (ORCPT ); Wed, 6 Mar 2019 04:56:56 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x269uR9k1654018 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Wed, 6 Mar 2019 01:56:27 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x269uRQj1654014; Wed, 6 Mar 2019 01:56:27 -0800 Date: Wed, 6 Mar 2019 01:56:27 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Kees Cook Message-ID: Cc: mingo@kernel.org, linux@dominikbrodowski.net, gregkh@linuxfoundation.org, sean.j.christopherson@intel.com, kernel-hardening@lists.openwall.com, solar@openwall.com, jannh@google.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, peterz@infradead.org, hpa@zytor.com, keescook@chromium.org Reply-To: jannh@google.com, solar@openwall.com, sean.j.christopherson@intel.com, kernel-hardening@lists.openwall.com, linux@dominikbrodowski.net, gregkh@linuxfoundation.org, mingo@kernel.org, keescook@chromium.org, tglx@linutronix.de, hpa@zytor.com, peterz@infradead.org, linux-kernel@vger.kernel.org In-Reply-To: <20190227200132.24707-4-keescook@chromium.org> References: <20190227200132.24707-4-keescook@chromium.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] lkdtm: Check for SMEP clearing protections Git-Commit-ID: a0bf7fc24303a538396aa8d32450d05c1929b9f0 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: a0bf7fc24303a538396aa8d32450d05c1929b9f0 Gitweb: https://git.kernel.org/tip/a0bf7fc24303a538396aa8d32450d05c1929b9f0 Author: Kees Cook AuthorDate: Wed, 27 Feb 2019 12:01:32 -0800 Committer: Thomas Gleixner CommitDate: Wed, 6 Mar 2019 10:49:50 +0100 lkdtm: Check for SMEP clearing protections 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 Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Solar Designer Cc: Greg KH Cc: Jann Horn Cc: Sean Christopherson Cc: Dominik Brodowski Cc: Kernel Hardening Link: https://lkml.kernel.org/r/20190227200132.24707-4-keescook@chromium.org --- drivers/misc/lkdtm/bugs.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + 3 files changed, 63 insertions(+) diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 7eebbdfbcacd..6176384b4f85 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -255,3 +255,64 @@ void lkdtm_STACK_GUARD_PAGE_TRAILING(void) pr_err("FAIL: accessed page after stack!\n"); } + +void lkdtm_UNSET_SMEP(void) +{ +#ifdef CONFIG_X86_64 +#define MOV_CR4_DEPTH 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 < MOV_CR4_DEPTH; i++) { + /* mov %rdi, %cr4 */ + if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) + break; + } + if (i >= MOV_CR4_DEPTH) { + 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);