From patchwork Tue Apr 21 02:14:42 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sami Tolvanen X-Patchwork-Id: 11500229 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D876E13B2 for ; Tue, 21 Apr 2020 02:15:20 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 16920208E4 for ; Tue, 21 Apr 2020 02:15:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="f4mnh0pW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 16920208E4 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18584-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 16327 invoked by uid 550); 21 Apr 2020 02:15:13 -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 16211 invoked from network); 21 Apr 2020 02:15:12 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=O6cTFRpJP9X3Ho0tpm44ZbomQwaxFpLQPG8cGKQ1jrA=; b=f4mnh0pWascSaL/AdPEF4DCvaJe9pCemAfTP8Gw89vOMOoMs8q9dTjr695yMJKQp1I 1Vf0ZDH4iuIajPbqdYOWdIrd43AsJf+NoxSmgKDKQMHlyTmoDsaygA1K/mLok1Xkv5m1 Dv48+mhATsC3sLN5BxllxfM74jy5zYpXv5nP9Sq7R9GxZs8P1QbjkgKbNuNshL/Ptmha sC8m2yQoQdWi7tHEK5fTZ9iW+PUqrFWkpC6Tap6qwRQUKCxmIxGHOsIu4H+SyqrUPSJO Cgvm6dCjLy2fBOcabEZdaN73wPtfzTz2P+aFwzpPOqqbtCm/OIBU41ggdzw1zdorSj60 voOg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=O6cTFRpJP9X3Ho0tpm44ZbomQwaxFpLQPG8cGKQ1jrA=; b=ZFrhXvN9/GlsV9Zd5gVCMjxTf0NRnUmVWv+db0HbcgQ7Yl+fzm7vQ3CitNO3Nia5Hz nrwWABGlwhnaSaSjAXqNHaWdH6AjFHpHovBgkcvioqtfgv5mM+vpSuZQKY0CHMsMM1OX oLPp7MPzReCiBRfMP6hQZhTvE2B6EvYJTsT0EkwXvVbCqQ6shTdFSTK8umLl9FSwtigV KZCqgSx4toJl77KqWQQFd1zCfwnwAFDQ1UdowTeHVHf5aEsDgHy0X4LCkY+uPS8yd1h7 LyY94Fexbrx0PmFvGI4agnwDAbH1aSSeA0YwHIVaYXfx4TqFTtlwZlDUMndJ0zBXwWZ5 VeAQ== X-Gm-Message-State: AGi0PuY2qYhVete8QIwPaREZjgysDB74qz7HlJqb9zd2/hg2aUzmQ+ix hqoZ4VAZ0mdDWefLyt00L9fXDnTI1tXjfTl0bKI= X-Google-Smtp-Source: APiQypIHbEzVxzubxTWmbw4MJ4MzHiHfzQFCP034NZX7geCp0IXB6bGrLCcMJgUDsaG3JKRXB1YZ4+cAgIWLKLxGuAk= X-Received: by 2002:a63:5b57:: with SMTP id l23mr5400781pgm.391.1587435299723; Mon, 20 Apr 2020 19:14:59 -0700 (PDT) Date: Mon, 20 Apr 2020 19:14:42 -0700 In-Reply-To: <20200421021453.198187-1-samitolvanen@google.com> Message-Id: <20200421021453.198187-2-samitolvanen@google.com> Mime-Version: 1.0 References: <20191018161033.261971-1-samitolvanen@google.com> <20200421021453.198187-1-samitolvanen@google.com> X-Mailer: git-send-email 2.26.1.301.g55bc3eb7cb9-goog Subject: [PATCH v12 01/12] add support for Clang's Shadow Call Stack (SCS) From: Sami Tolvanen To: Will Deacon , Catalin Marinas , James Morse , Steven Rostedt , Ard Biesheuvel , Mark Rutland , Masahiro Yamada , Michal Marek , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot Cc: Dave Martin , Kees Cook , Laura Abbott , Marc Zyngier , Masami Hiramatsu , Nick Desaulniers , Jann Horn , Miguel Ojeda , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Sami Tolvanen This change adds generic support for Clang's Shadow Call Stack, which uses a shadow stack to protect return addresses from being overwritten by an attacker. Details are available here: https://clang.llvm.org/docs/ShadowCallStack.html Note that security guarantees in the kernel differ from the ones documented for user space. The kernel must store addresses of shadow stacks used by other tasks and interrupt handlers in memory, which means an attacker capable reading and writing arbitrary memory may be able to locate them and hijack control flow by modifying shadow stacks that are not currently in use. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Reviewed-by: Miguel Ojeda --- Makefile | 6 +++ arch/Kconfig | 25 +++++++++ include/linux/compiler-clang.h | 6 +++ include/linux/compiler_types.h | 4 ++ include/linux/scs.h | 92 ++++++++++++++++++++++++++++++++++ init/init_task.c | 8 +++ kernel/Makefile | 1 + kernel/fork.c | 9 ++++ kernel/sched/core.c | 2 + kernel/scs.c | 67 +++++++++++++++++++++++++ 10 files changed, 220 insertions(+) create mode 100644 include/linux/scs.h create mode 100644 kernel/scs.c diff --git a/Makefile b/Makefile index 49b2709ff44e..6094db2c7252 100644 --- a/Makefile +++ b/Makefile @@ -866,6 +866,12 @@ ifdef CONFIG_LIVEPATCH KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone) endif +ifdef CONFIG_SHADOW_CALL_STACK +CC_FLAGS_SCS := -fsanitize=shadow-call-stack +KBUILD_CFLAGS += $(CC_FLAGS_SCS) +export CC_FLAGS_SCS +endif + # arch Makefile may override CC so keep this after arch Makefile is included NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) diff --git a/arch/Kconfig b/arch/Kconfig index 786a85d4ad40..8450d56e6af6 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -533,6 +533,31 @@ config STACKPROTECTOR_STRONG about 20% of all kernel functions, which increases the kernel code size by about 2%. +config ARCH_SUPPORTS_SHADOW_CALL_STACK + bool + help + An architecture should select this if it supports Clang's Shadow + Call Stack, has asm/scs.h, and implements runtime support for shadow + stack switching. + +config SHADOW_CALL_STACK + bool "Clang Shadow Call Stack" + depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK + help + This option enables Clang's Shadow Call Stack, which uses a + shadow stack to protect function return addresses from being + overwritten by an attacker. More information can be found in + Clang's documentation: + + https://clang.llvm.org/docs/ShadowCallStack.html + + Note that security guarantees in the kernel differ from the ones + documented for user space. The kernel must store addresses of shadow + stacks used by other tasks and interrupt handlers in memory, which + means an attacker capable of reading and writing arbitrary memory + may be able to locate them and hijack control flow by modifying + shadow stacks that are not currently in use. + config HAVE_ARCH_WITHIN_STACK_FRAMES bool help diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index 333a6695a918..18fc4d29ef27 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -42,3 +42,9 @@ * compilers, like ICC. */ #define barrier() __asm__ __volatile__("" : : : "memory") + +#if __has_feature(shadow_call_stack) +# define __noscs __attribute__((__no_sanitize__("shadow-call-stack"))) +#else +# define __noscs +#endif diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index e970f97a7fcb..97b62f47a80d 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -193,6 +193,10 @@ struct ftrace_likely_data { # define randomized_struct_fields_end #endif +#ifndef __noscs +# define __noscs +#endif + #ifndef asm_volatile_goto #define asm_volatile_goto(x...) asm goto(x) #endif diff --git a/include/linux/scs.h b/include/linux/scs.h new file mode 100644 index 000000000000..051d27ad3da4 --- /dev/null +++ b/include/linux/scs.h @@ -0,0 +1,92 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Shadow Call Stack support. + * + * Copyright (C) 2019 Google LLC + */ + +#ifndef _LINUX_SCS_H +#define _LINUX_SCS_H + +#include +#include +#include +#include + +#ifdef CONFIG_SHADOW_CALL_STACK + +/* + * In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit + * architecture) provided ~40% safety margin on stack usage while keeping + * memory allocation overhead reasonable. + */ +#define SCS_SIZE 1024UL +#define GFP_SCS (GFP_KERNEL | __GFP_ZERO) + +/* An illegal pointer value to mark the end of the shadow stack. */ +#define SCS_END_MAGIC (0x5f6UL + POISON_POINTER_DELTA) + +#define task_scs(tsk) (task_thread_info(tsk)->shadow_call_stack) + +static inline void task_set_scs(struct task_struct *tsk, void *s) +{ + task_scs(tsk) = s; +} + +extern void scs_init(void); + +static inline void *__scs_base(struct task_struct *tsk) +{ + /* + * To minimize the risk of exposure, architectures may clear a + * task's thread_info::shadow_call_stack while that task is + * running, and only save/restore the active shadow call stack + * pointer when the usual register may be clobbered (e.g. across + * context switches). + * + * The shadow call stack is aligned to SCS_SIZE, and grows + * upwards, so we can mask out the low bits to extract the base + * when the task is not running. + */ + return (void *)((unsigned long)task_scs(tsk) & ~(SCS_SIZE - 1)); +} + +static inline void scs_task_reset(struct task_struct *tsk) +{ + /* + * Reset the shadow stack to the base address in case the task + * is reused. + */ + task_set_scs(tsk, __scs_base(tsk)); +} + +extern int scs_prepare(struct task_struct *tsk, int node); + +static inline unsigned long *__scs_magic(void *s) +{ + return (unsigned long *)(s + SCS_SIZE) - 1; +} + +static inline bool scs_corrupted(struct task_struct *tsk) +{ + unsigned long *magic = __scs_magic(__scs_base(tsk)); + + return READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC; +} + +extern void scs_release(struct task_struct *tsk); + +#else /* CONFIG_SHADOW_CALL_STACK */ + +#define task_scs(tsk) NULL + +static inline void task_set_scs(struct task_struct *tsk, void *s) {} +static inline void scs_init(void) {} +static inline void scs_task_reset(struct task_struct *tsk) {} +static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; } +static inline bool scs_corrupted(struct task_struct *tsk) { return false; } +static inline void scs_release(struct task_struct *tsk) {} + +#endif /* CONFIG_SHADOW_CALL_STACK */ + +#endif /* _LINUX_SCS_H */ diff --git a/init/init_task.c b/init/init_task.c index bd403ed3e418..aaa71366d162 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #include @@ -185,6 +186,13 @@ struct task_struct init_task }; EXPORT_SYMBOL(init_task); +#ifdef CONFIG_SHADOW_CALL_STACK +unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)] __init_task_data + __aligned(SCS_SIZE) = { + [(SCS_SIZE / sizeof(long)) - 1] = SCS_END_MAGIC +}; +#endif + /* * Initial thread structure. Alignment of this is handled by a special * linker map entry. diff --git a/kernel/Makefile b/kernel/Makefile index 4cb4130ced32..c332eb9d4841 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -103,6 +103,7 @@ obj-$(CONFIG_TRACEPOINTS) += trace/ obj-$(CONFIG_IRQ_WORK) += irq_work.o obj-$(CONFIG_CPU_PM) += cpu_pm.o obj-$(CONFIG_BPF) += bpf/ +obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o obj-$(CONFIG_PERF_EVENTS) += events/ diff --git a/kernel/fork.c b/kernel/fork.c index 8c700f881d92..f6339f9d232d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -94,6 +94,7 @@ #include #include #include +#include #include #include @@ -456,6 +457,8 @@ void put_task_stack(struct task_struct *tsk) void free_task(struct task_struct *tsk) { + scs_release(tsk); + #ifndef CONFIG_THREAD_INFO_IN_TASK /* * The task is finally done with both the stack and thread_info, @@ -840,6 +843,8 @@ void __init fork_init(void) NULL, free_vm_stack_cache); #endif + scs_init(); + lockdep_init_task(&init_task); uprobes_init(); } @@ -899,6 +904,10 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) if (err) goto free_stack; + err = scs_prepare(tsk, node); + if (err) + goto free_stack; + #ifdef CONFIG_SECCOMP /* * We must handle setting up seccomp filters once we're under diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3a61a3b8eaa9..c99620c1ec20 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -11,6 +11,7 @@ #include #include +#include #include #include @@ -6045,6 +6046,7 @@ void init_idle(struct task_struct *idle, int cpu) idle->se.exec_start = sched_clock(); idle->flags |= PF_IDLE; + scs_task_reset(idle); kasan_unpoison_task_stack(idle); #ifdef CONFIG_SMP diff --git a/kernel/scs.c b/kernel/scs.c new file mode 100644 index 000000000000..e1a8fc453b86 --- /dev/null +++ b/kernel/scs.c @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Shadow Call Stack support. + * + * Copyright (C) 2019 Google LLC + */ + +#include +#include +#include +#include + +static struct kmem_cache *scs_cache; + +static void *scs_alloc(int node) +{ + void *s; + + s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node); + if (s) { + *__scs_magic(s) = SCS_END_MAGIC; + /* + * Poison the allocation to catch unintentional accesses to + * the shadow stack when KASAN is enabled. + */ + kasan_poison_object_data(scs_cache, s); + } + + return s; +} + +static void scs_free(void *s) +{ + kasan_unpoison_object_data(scs_cache, s); + kmem_cache_free(scs_cache, s); +} + +void __init scs_init(void) +{ + scs_cache = kmem_cache_create("scs_cache", SCS_SIZE, SCS_SIZE, + 0, NULL); +} + +int scs_prepare(struct task_struct *tsk, int node) +{ + void *s; + + s = scs_alloc(node); + if (!s) + return -ENOMEM; + + task_set_scs(tsk, s); + return 0; +} + +void scs_release(struct task_struct *tsk) +{ + void *s; + + s = __scs_base(tsk); + if (!s) + return; + + WARN_ON(scs_corrupted(tsk)); + + scs_free(s); +}