From patchwork Thu Aug 16 22:17:03 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Popov X-Patchwork-Id: 10568259 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 8F51313B4 for ; Thu, 16 Aug 2018 22:18:55 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7E6B12B8C4 for ; Thu, 16 Aug 2018 22:18:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 71CEC2B8C8; Thu, 16 Aug 2018 22:18:55 +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=-5.2 required=2.0 tests=BAYES_00,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 2F1042B8C4 for ; Thu, 16 Aug 2018 22:18:53 +0000 (UTC) Received: (qmail 28539 invoked by uid 550); 16 Aug 2018 22:17:58 -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 28438 invoked from network); 16 Aug 2018 22:17:55 -0000 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:subject:date:message-id:in-reply-to :references; bh=sLY8qiJnk0q5uyehVafm6Ppe03lAKU5AlZIBFnCJIHg=; b=kGZcyBq+kv3arjnq+fwHXLJSydM9f190371H3twWsYj6qHweUxf95lxiaOmUNM3zTk ujUgAX99auVNfMCq0jG7BsDfcaUPmWoBLJDE7T4LBhvi5x/i3+QAD628l8GPykhC5YcE +x/DHYlKJAr9GGRS0Anse4GYGBsrrD3T2X/NKj9R5JMP1cRFJvKujQmJ4gALdqFpfZCQ lQnn0MM7232xiCrhf3rrt3129pALgchsOe8mGiiSoQQbCIdkBMRFaJE00XBQ1IkcAZes 4U8WwkXVSevT2iqRy4jQFFs9ZvWhql5m7aMUDpWMxBSQqdj55i1NtxwKdKj6XZ+aB1RN vZyA== X-Gm-Message-State: AOUpUlH8XXtHyFtICfaoiu1q5rJowQsWbdDS2WAoi70mGcvdMnUFBFM/ Ri6m2ykPF6swyhgpMk6HIJnqQn9aYdA= X-Google-Smtp-Source: AA+uWPw9UiEOic4iCDmpxQ0A5Yn4KOgAgHcb27l9i5hkq1G/hJFU3EAKNmCGPvs3qYcMJ1NrRTQtfg== X-Received: by 2002:a19:7b08:: with SMTP id w8-v6mr20214167lfc.22.1534457864173; Thu, 16 Aug 2018 15:17:44 -0700 (PDT) From: Alexander Popov To: kernel-hardening@lists.openwall.com, Kees Cook , PaX Team , Brad Spengler , Ingo Molnar , Andy Lutomirski , Tycho Andersen , Laura Abbott , Mark Rutland , Ard Biesheuvel , Borislav Petkov , Richard Sandiford , Thomas Gleixner , "H . Peter Anvin" , Peter Zijlstra , "Dmitry V . Levin" , Emese Revfy , Jonathan Corbet , Andrey Ryabinin , "Kirill A . Shutemov" , Thomas Garnier , Andrew Morton , Alexei Starovoitov , Josef Bacik , Masami Hiramatsu , Nicholas Piggin , Al Viro , "David S . Miller" , Ding Tianhong , David Woodhouse , Josh Poimboeuf , Steven Rostedt , Dominik Brodowski , Juergen Gross , Linus Torvalds , Greg Kroah-Hartman , Dan Williams , Dave Hansen , Mathias Krause , Vikas Shivappa , Kyle Huey , Dmitry Safonov , Will Deacon , Arnd Bergmann , Florian Weimer , Boris Lukashev , Andrey Konovalov , x86@kernel.org, linux-kernel@vger.kernel.org, alex.popov@linux.com Subject: [PATCH v15 6/7] stackleak: Allow runtime disabling of kernel stack erasing Date: Fri, 17 Aug 2018 01:17:03 +0300 Message-Id: <1534457824-7211-7-git-send-email-alex.popov@linux.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1534457824-7211-1-git-send-email-alex.popov@linux.com> References: <1534457824-7211-1-git-send-email-alex.popov@linux.com> X-Virus-Scanned: ClamAV using ClamSMTP Introduce CONFIG_STACKLEAK_RUNTIME_DISABLE option, which provides 'stack_erasing' sysctl. It can be used in runtime to control kernel stack erasing for kernels built with CONFIG_GCC_PLUGIN_STACKLEAK. Suggested-by: Ingo Molnar Signed-off-by: Alexander Popov --- Documentation/sysctl/kernel.txt | 18 ++++++++++++++++++ include/linux/stackleak.h | 6 ++++++ kernel/stackleak.c | 38 ++++++++++++++++++++++++++++++++++++++ kernel/sysctl.c | 15 ++++++++++++++- scripts/gcc-plugins/Kconfig | 8 ++++++++ 5 files changed, 84 insertions(+), 1 deletion(-) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index eded671d..1feae79 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -87,6 +87,7 @@ show up in /proc/sys/kernel: - shmmni - softlockup_all_cpu_backtrace - soft_watchdog +- stack_erasing - stop-a [ SPARC only ] - sysrq ==> Documentation/admin-guide/sysrq.rst - sysctl_writes_strict @@ -962,6 +963,23 @@ detect a hard lockup condition. ============================================================== +stack_erasing + +This parameter can be used to control kernel stack erasing at the end +of syscalls for kernels built with CONFIG_GCC_PLUGIN_STACKLEAK. + +That erasing reduces the information which kernel stack leak bugs +can reveal and blocks some uninitialized stack variable attacks. +The tradeoff is the performance impact: on a single CPU system kernel +compilation sees a 1% slowdown, other systems and workloads may vary. + + 0: kernel stack erasing is disabled, STACKLEAK_METRICS are not updated. + + 1: kernel stack erasing is enabled (default), it is performed before + returning to the userspace at the end of syscalls. + +============================================================== + tainted: Non-zero if the kernel has been tainted. Numeric values, which can be diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h index b911b97..3d5c327 100644 --- a/include/linux/stackleak.h +++ b/include/linux/stackleak.h @@ -22,6 +22,12 @@ static inline void stackleak_task_init(struct task_struct *t) t->prev_lowest_stack = t->lowest_stack; # endif } + +#ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE +int stack_erasing_sysctl(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos); +#endif + #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */ static inline void stackleak_task_init(struct task_struct *t) { } #endif diff --git a/kernel/stackleak.c b/kernel/stackleak.c index f662395..e428929 100644 --- a/kernel/stackleak.c +++ b/kernel/stackleak.c @@ -12,6 +12,41 @@ #include +#ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE +#include +#include + +static DEFINE_STATIC_KEY_FALSE(stack_erasing_bypass); + +int stack_erasing_sysctl(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int ret = 0; + int state = !static_branch_unlikely(&stack_erasing_bypass); + int prev_state = state; + + table->data = &state; + table->maxlen = sizeof(int); + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + state = !!state; + if (ret || !write || state == prev_state) + return ret; + + if (state) + static_branch_disable(&stack_erasing_bypass); + else + static_branch_enable(&stack_erasing_bypass); + + pr_warn("stackleak: kernel stack erasing is %s\n", + state ? "enabled" : "disabled"); + return ret; +} + +#define skip_erasing() static_branch_unlikely(&stack_erasing_bypass) +#else +#define skip_erasing() false +#endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */ + asmlinkage void stackleak_erase(void) { /* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */ @@ -20,6 +55,9 @@ asmlinkage void stackleak_erase(void) unsigned int poison_count = 0; const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long); + if (skip_erasing()) + return; + /* Check that 'lowest_stack' value is sane */ if (unlikely(kstack_ptr - boundary >= THREAD_SIZE)) kstack_ptr = boundary; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index f22f76b..faa216d 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -91,7 +91,9 @@ #ifdef CONFIG_CHR_DEV_SG #include #endif - +#ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE +#include +#endif #ifdef CONFIG_LOCKUP_DETECTOR #include #endif @@ -1222,6 +1224,17 @@ static struct ctl_table kern_table[] = { .extra2 = &one, }, #endif +#ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE + { + .procname = "stack_erasing", + .data = NULL, + .maxlen = sizeof(int), + .mode = 0600, + .proc_handler = stack_erasing_sysctl, + .extra1 = &zero, + .extra2 = &one, + }, +#endif { } }; diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig index f15093b..8b01c8e 100644 --- a/scripts/gcc-plugins/Kconfig +++ b/scripts/gcc-plugins/Kconfig @@ -182,4 +182,12 @@ config STACKLEAK_METRICS can be useful for estimating the STACKLEAK performance impact for your workloads. +config STACKLEAK_RUNTIME_DISABLE + bool "Allow runtime disabling of kernel stack erasing" + depends on GCC_PLUGIN_STACKLEAK + help + This option provides 'stack_erasing' sysctl, which can be used in + runtime to control kernel stack erasing for kernels built with + CONFIG_GCC_PLUGIN_STACKLEAK. + endif