From patchwork Tue Jun 18 04:55:01 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 11000895 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BB57E14DB for ; Tue, 18 Jun 2019 04:55:50 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id AC06A287E5 for ; Tue, 18 Jun 2019 04:55:50 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A046728979; Tue, 18 Jun 2019 04:55:50 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 88B16287E5 for ; Tue, 18 Jun 2019 04:55:49 +0000 (UTC) Received: (qmail 19900 invoked by uid 550); 18 Jun 2019 04:55:24 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 19769 invoked from network); 18 Jun 2019 04:55:21 -0000 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=qnStX17gprC4EO3JslfOKqvuRlw//DOp35gcW3WHxCs=; b=QFjbYmGJrCOeph3wo/lPROf1twpnMNCBoCurylkTc1w+8wzef3vU05t7FapRwubwqZ Ld2fdhXxahLeFTTSVZ2EQ8KnI1JjFdknbkYfZXN4dW2wR3ik0yl1ZEsbXa2nA/rxfUbT wPySjJ6fbla/F11m/fH6O6VN2PwJBuzlxdUTk= 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=qnStX17gprC4EO3JslfOKqvuRlw//DOp35gcW3WHxCs=; b=hZ6X5DsHPLGSN2PGyXTacsR1aUWSsCqzxDQLZzbeEkRy6nv7Y0qdp0wPgFZoTxgzwk 2wkh9oxV34VGurOBblwL0vc4XAZVEAt9MiLWGETlMchmG+0YcFCUtRIg5rLtDfEPpiKw SrcbMJImY3G9TuzB7wQphcwRRJ07E74E57pwfdkEzTeN3Ti/hvbAEFVZYyLZDYnb1xal geD19qf//wCT5PDsU8BegCfDMXg86CbLoseI77uT7xxPBdVHzViWksWoNf40TYYgVDWG BqsMHLcHR2sKZcvH/U4UQPaYrj8QGWJCn0qnfQglDovJKbNTymFrXjV7I3zXXEIaxAf9 Kqfg== X-Gm-Message-State: APjAAAWEsNtJX391i1YKY3BWzXM34yR+VqybzquNgKDIScGLoaznaG8v uo9uzIjgJQyrL/A+DB8obY8cRA== X-Google-Smtp-Source: APXvYqzegS8FdaYYJ9tUvTEawroRiXm2ywlT9vgjrGEqGUYD2udBCjG/A1A/lyVqmE62G1Ui+eNFbQ== X-Received: by 2002:aa7:86c6:: with SMTP id h6mr81450477pfo.51.1560833709869; Mon, 17 Jun 2019 21:55:09 -0700 (PDT) From: Kees Cook To: Thomas Gleixner Cc: Kees Cook , Linus Torvalds , x86@kernel.org, Peter Zijlstra , Dave Hansen , linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v3 1/3] lkdtm: Check for SMEP clearing protections Date: Mon, 17 Jun 2019 21:55:01 -0700 Message-Id: <20190618045503.39105-2-keescook@chromium.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190618045503.39105-1-keescook@chromium.org> References: <20190618045503.39105-1-keescook@chromium.org> X-Virus-Scanned: ClamAV using ClamSMTP 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 [ 79.601810] ------------[ cut here ]------------ [ 79.603421] Attempt to unpin cr4 bits: 100000; bypass attack?! ... [ 79.650170] ---[ end trace 2452ca0f6126242e ]--- [ 79.652281] lkdtm: ok: SMEP did not get cleared [ 79.654344] lkdtm: trying to clear SMEP with call gadget [ 79.655937] lkdtm: ok: SMEP removal was reverted Signed-off-by: Kees Cook --- drivers/misc/lkdtm/bugs.c | 66 ++++++++++++++++++++++++++++++++++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + 3 files changed, 68 insertions(+) diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 7eebbdfbcacd..3edf4464b9fc 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -255,3 +255,69 @@ 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; + /* mov %rdi,%rax; mov %rax, %cr4 */ + if (insn[i] == 0x48 && insn[i+1] == 0x89 && + insn[i+2] == 0xf8 && insn[i+3] == 0x0f && + insn[i+4] == 0x22 && insn[i+5] == 0xe0) + 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 b51cf182b031..58cfd713f8dc 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -123,6 +123,7 @@ 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 b69ee004a3f7..d7eb5a8f1da4 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);