This patch adds basic shadow stack enabling/disabling routines. A task's shadow stack is allocated from memory with VM_SHSTK flag set and read-only protection. It has a fixed size of RLIMIT_STACK. Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> --- arch/x86/include/asm/cet.h | 34 +++++ arch/x86/include/asm/disabled-features.h | 8 +- arch/x86/include/asm/msr-index.h | 18 +++ arch/x86/include/asm/processor.h | 5 + arch/x86/kernel/Makefile | 2 + arch/x86/kernel/cet.c | 116 ++++++++++++++++++ arch/x86/kernel/cpu/common.c | 25 ++++ arch/x86/kernel/process.c | 1 + .../arch/x86/include/asm/disabled-features.h | 8 +- 9 files changed, 215 insertions(+), 2 deletions(-) create mode 100644 arch/x86/include/asm/cet.h create mode 100644 arch/x86/kernel/cet.c diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h new file mode 100644 index 000000000000..c952a2ec65fe --- /dev/null +++ b/arch/x86/include/asm/cet.h @@ -0,0 +1,34 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_X86_CET_H +#define _ASM_X86_CET_H + +#ifndef __ASSEMBLY__ +#include <linux/types.h> + +struct task_struct; +/* + * Per-thread CET status + */ +struct cet_status { + unsigned long shstk_base; + unsigned long shstk_size; + unsigned int shstk_enabled:1; +}; + +#ifdef CONFIG_X86_INTEL_CET +int cet_setup_shstk(void); +void cet_disable_shstk(void); +void cet_disable_free_shstk(struct task_struct *p); +#else +static inline int cet_setup_shstk(void) { return -EINVAL; } +static inline void cet_disable_shstk(void) {} +static inline void cet_disable_free_shstk(struct task_struct *p) {} +#endif + +#define cpu_x86_cet_enabled() \ + (cpu_feature_enabled(X86_FEATURE_SHSTK) || \ + cpu_feature_enabled(X86_FEATURE_IBT)) + +#endif /* __ASSEMBLY__ */ + +#endif /* _ASM_X86_CET_H */ diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h index a5ea841cc6d2..06323ebed643 100644 --- a/arch/x86/include/asm/disabled-features.h +++ b/arch/x86/include/asm/disabled-features.h @@ -62,6 +62,12 @@ # define DISABLE_PTI (1 << (X86_FEATURE_PTI & 31)) #endif +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER +#define DISABLE_SHSTK 0 +#else +#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31)) +#endif + /* * Make sure to add features to the correct mask */ @@ -81,7 +87,7 @@ #define DISABLED_MASK13 0 #define DISABLED_MASK14 0 #define DISABLED_MASK15 0 -#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP) +#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK) #define DISABLED_MASK17 0 #define DISABLED_MASK18 0 #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19) diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 979ef971cc78..30e9107974fa 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -839,4 +839,22 @@ #define MSR_VM_IGNNE 0xc0010115 #define MSR_VM_HSAVE_PA 0xc0010117 +/* Control-flow Enforcement Technology MSRs */ +#define MSR_IA32_U_CET 0x6a0 /* user mode cet setting */ +#define MSR_IA32_S_CET 0x6a2 /* kernel mode cet setting */ +#define MSR_IA32_PL0_SSP 0x6a4 /* kernel shstk pointer */ +#define MSR_IA32_PL1_SSP 0x6a5 /* ring-1 shstk pointer */ +#define MSR_IA32_PL2_SSP 0x6a6 /* ring-2 shstk pointer */ +#define MSR_IA32_PL3_SSP 0x6a7 /* user shstk pointer */ +#define MSR_IA32_INT_SSP_TAB 0x6a8 /* exception shstk table */ + +/* MSR_IA32_U_CET and MSR_IA32_S_CET bits */ +#define MSR_IA32_CET_SHSTK_EN 0x0000000000000001ULL +#define MSR_IA32_CET_WRSS_EN 0x0000000000000002ULL +#define MSR_IA32_CET_ENDBR_EN 0x0000000000000004ULL +#define MSR_IA32_CET_LEG_IW_EN 0x0000000000000008ULL +#define MSR_IA32_CET_NO_TRACK_EN 0x0000000000000010ULL +#define MSR_IA32_CET_WAIT_ENDBR 0x00000000000000800UL +#define MSR_IA32_CET_BITMAP_MASK 0xfffffffffffff000ULL + #endif /* _ASM_X86_MSR_INDEX_H */ diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index c34a35c78618..2ae7c1bf4e43 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -24,6 +24,7 @@ struct vm86; #include <asm/special_insns.h> #include <asm/fpu/types.h> #include <asm/unwind_hints.h> +#include <asm/cet.h> #include <linux/personality.h> #include <linux/cache.h> @@ -487,6 +488,10 @@ struct thread_struct { unsigned int sig_on_uaccess_err:1; unsigned int uaccess_err:1; /* uaccess failed */ +#ifdef CONFIG_X86_INTEL_CET + struct cet_status cet; +#endif + /* Floating point and extended processor state */ struct fpu fpu; /* diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index ce1b5cc360a2..584ed7e9a599 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -140,6 +140,8 @@ obj-$(CONFIG_UNWINDER_ORC) += unwind_orc.o obj-$(CONFIG_UNWINDER_FRAME_POINTER) += unwind_frame.o obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o +obj-$(CONFIG_X86_INTEL_CET) += cet.o + ### # 64 bit specific files ifeq ($(CONFIG_X86_64),y) diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c new file mode 100644 index 000000000000..2a48634aa6ce --- /dev/null +++ b/arch/x86/kernel/cet.c @@ -0,0 +1,116 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * cet.c - Control-flow Enforcement (CET) + * + * Copyright (c) 2018, Intel Corporation. + * Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> + */ + +#include <linux/types.h> +#include <linux/mm.h> +#include <linux/mman.h> +#include <linux/slab.h> +#include <linux/uaccess.h> +#include <linux/sched/signal.h> +#include <linux/compat.h> +#include <asm/msr.h> +#include <asm/user.h> +#include <asm/fpu/internal.h> +#include <asm/fpu/xstate.h> +#include <asm/fpu/types.h> +#include <asm/cet.h> + +static int set_shstk_ptr(unsigned long addr) +{ + u64 r; + + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return -1; + + if ((addr >= TASK_SIZE_MAX) || (!IS_ALIGNED(addr, 4))) + return -1; + + modify_fpu_regs_begin(); + rdmsrl(MSR_IA32_U_CET, r); + wrmsrl(MSR_IA32_PL3_SSP, addr); + wrmsrl(MSR_IA32_U_CET, r | MSR_IA32_CET_SHSTK_EN); + modify_fpu_regs_end(); + return 0; +} + +static unsigned long get_shstk_addr(void) +{ + unsigned long ptr; + + if (!current->thread.cet.shstk_enabled) + return 0; + + modify_fpu_regs_begin(); + rdmsrl(MSR_IA32_PL3_SSP, ptr); + modify_fpu_regs_end(); + return ptr; +} + +int cet_setup_shstk(void) +{ + unsigned long addr, size; + + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return -EOPNOTSUPP; + + size = rlimit(RLIMIT_STACK); + addr = do_mmap_locked(0, size, PROT_READ, + MAP_ANONYMOUS | MAP_PRIVATE, VM_SHSTK); + + /* + * Return actual error from do_mmap(). + */ + if (addr >= TASK_SIZE_MAX) + return addr; + + set_shstk_ptr(addr + size - sizeof(u64)); + current->thread.cet.shstk_base = addr; + current->thread.cet.shstk_size = size; + current->thread.cet.shstk_enabled = 1; + return 0; +} + +void cet_disable_shstk(void) +{ + u64 r; + + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return; + + modify_fpu_regs_begin(); + rdmsrl(MSR_IA32_U_CET, r); + r &= ~(MSR_IA32_CET_SHSTK_EN); + wrmsrl(MSR_IA32_U_CET, r); + wrmsrl(MSR_IA32_PL3_SSP, 0); + modify_fpu_regs_end(); + current->thread.cet.shstk_enabled = 0; +} + +void cet_disable_free_shstk(struct task_struct *tsk) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK) || + !tsk->thread.cet.shstk_enabled) + return; + + if (tsk->mm && (tsk == current)) + cet_disable_shstk(); + + /* + * Free only when tsk is current or shares mm + * with current but has its own shstk. + */ + if (tsk->mm && (tsk->mm == current->mm) && + (tsk->thread.cet.shstk_base)) { + vm_munmap(tsk->thread.cet.shstk_base, + tsk->thread.cet.shstk_size); + tsk->thread.cet.shstk_base = 0; + tsk->thread.cet.shstk_size = 0; + } + + tsk->thread.cet.shstk_enabled = 0; +} diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 2c57fffebf9b..b0780fe8717e 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -53,6 +53,7 @@ #include <asm/microcode_intel.h> #include <asm/intel-family.h> #include <asm/cpu_device_id.h> +#include <asm/cet.h> #ifdef CONFIG_X86_LOCAL_APIC #include <asm/uv/uv.h> @@ -417,6 +418,29 @@ static __init int setup_disable_pku(char *arg) __setup("nopku", setup_disable_pku); #endif /* CONFIG_X86_64 */ +static __always_inline void setup_cet(struct cpuinfo_x86 *c) +{ + if (cpu_x86_cet_enabled()) + cr4_set_bits(X86_CR4_CET); +} + +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER +static __init int setup_disable_shstk(char *s) +{ + /* require an exact match without trailing characters */ + if (s[0] != '\0') + return 0; + + if (!boot_cpu_has(X86_FEATURE_SHSTK)) + return 1; + + setup_clear_cpu_cap(X86_FEATURE_SHSTK); + pr_info("x86: 'no_cet_shstk' specified, disabling Shadow Stack\n"); + return 1; +} +__setup("no_cet_shstk", setup_disable_shstk); +#endif + /* * Some CPU features depend on higher CPUID levels, which may not always * be available due to CPUID level capping or broken virtualization @@ -1393,6 +1417,7 @@ static void identify_cpu(struct cpuinfo_x86 *c) x86_init_rdrand(c); x86_init_cache_qos(c); setup_pku(c); + setup_cet(c); /* * Clear/Set all flags overridden by options, need do it diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index d360bf4d696b..a4deb79b1089 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -42,6 +42,7 @@ #include <asm/prctl.h> #include <asm/spec-ctrl.h> #include <asm/proto.h> +#include <asm/cet.h> #include "process.h" diff --git a/tools/arch/x86/include/asm/disabled-features.h b/tools/arch/x86/include/asm/disabled-features.h index a5ea841cc6d2..06323ebed643 100644 --- a/tools/arch/x86/include/asm/disabled-features.h +++ b/tools/arch/x86/include/asm/disabled-features.h @@ -62,6 +62,12 @@ # define DISABLE_PTI (1 << (X86_FEATURE_PTI & 31)) #endif +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER +#define DISABLE_SHSTK 0 +#else +#define DISABLE_SHSTK (1<<(X86_FEATURE_SHSTK & 31)) +#endif + /* * Make sure to add features to the correct mask */ @@ -81,7 +87,7 @@ #define DISABLED_MASK13 0 #define DISABLED_MASK14 0 #define DISABLED_MASK15 0 -#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP) +#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP|DISABLE_SHSTK) #define DISABLED_MASK17 0 #define DISABLED_MASK18 0 #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19) -- 2.17.1