Intel supports faulting on the CPUID instruction in newer processors. Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is documented in detail in Section 2.3.2 of http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf Signed-off-by: Kyle Huey <khuey@xxxxxxxxxxxx> --- arch/x86/include/asm/msr-index.h | 1 + arch/x86/include/asm/thread_info.h | 4 +- arch/x86/include/uapi/asm/prctl.h | 6 + arch/x86/kernel/process.c | 81 +++++++++++ tools/testing/selftests/x86/Makefile | 2 +- tools/testing/selftests/x86/cpuid-fault.c | 223 ++++++++++++++++++++++++++++++ 6 files changed, 315 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/x86/cpuid-fault.c diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 83908d5..4aebec2 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -53,6 +53,7 @@ #define MSR_MTRRcap 0x000000fe #define MSR_IA32_BBL_CR_CTL 0x00000119 #define MSR_IA32_BBL_CR_CTL3 0x0000011e +#define MSR_MISC_FEATURES_ENABLES 0x00000140 #define MSR_IA32_SYSENTER_CS 0x00000174 #define MSR_IA32_SYSENTER_ESP 0x00000175 diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 8b7c8d8..ec93976 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -93,6 +93,7 @@ struct thread_info { #define TIF_SECCOMP 8 /* secure computing */ #define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */ #define TIF_UPROBE 12 /* breakpointed or singlestepping */ +#define TIF_NOCPUID 15 /* CPUID is not accessible in userland */ #define TIF_NOTSC 16 /* TSC is not accessible in userland */ #define TIF_IA32 17 /* IA32 compatibility process */ #define TIF_FORK 18 /* ret_from_fork */ @@ -117,6 +118,7 @@ struct thread_info { #define _TIF_SECCOMP (1 << TIF_SECCOMP) #define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY) #define _TIF_UPROBE (1 << TIF_UPROBE) +#define _TIF_NOCPUID (1 << TIF_NOCPUID) #define _TIF_NOTSC (1 << TIF_NOTSC) #define _TIF_IA32 (1 << TIF_IA32) #define _TIF_FORK (1 << TIF_FORK) @@ -146,7 +148,7 @@ struct thread_info { /* flags to check in __switch_to() */ #define _TIF_WORK_CTXSW \ - (_TIF_IO_BITMAP|_TIF_NOTSC|_TIF_BLOCKSTEP) + (_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP) #define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY) #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW) diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h index 3ac5032..c087e55 100644 --- a/arch/x86/include/uapi/asm/prctl.h +++ b/arch/x86/include/uapi/asm/prctl.h @@ -6,4 +6,10 @@ #define ARCH_GET_FS 0x1003 #define ARCH_GET_GS 0x1004 +/* Get/set the process' ability to use the CPUID instruction */ +#define ARCH_GET_CPUID 0x1005 +#define ARCH_SET_CPUID 0x1006 +# define ARCH_CPUID_ENABLE 1 /* allow the use of the CPUID instruction */ +# define ARCH_CPUID_SIGSEGV 2 /* throw a SIGSEGV instead of reading the CPUID */ + #endif /* _ASM_X86_PRCTL_H */ diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 0f857c3..5fc8e9d 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -193,6 +193,69 @@ int set_tsc_mode(unsigned int val) return 0; } +static void switch_cpuid_faulting(bool on) +{ + if (on) + msr_set_bit(MSR_MISC_FEATURES_ENABLES, 0); + else + msr_clear_bit(MSR_MISC_FEATURES_ENABLES, 0); +} + +static void disable_cpuid(void) +{ + preempt_disable(); + if (!test_and_set_thread_flag(TIF_NOCPUID)) + /* + * Must flip the CPU state synchronously with + * TIF_NOCPUID in the current running context. + */ + switch_cpuid_faulting(true); + preempt_enable(); +} + +static void enable_cpuid(void) +{ + preempt_disable(); + if (test_and_clear_thread_flag(TIF_NOCPUID)) + /* + * Must flip the CPU state synchronously with + * TIF_NOCPUID in the current running context. + */ + switch_cpuid_faulting(false); + preempt_enable(); +} + +int get_cpuid_mode(unsigned long adr) +{ + unsigned int val; + + if (test_thread_flag(TIF_NOCPUID)) + val = ARCH_CPUID_SIGSEGV; + else + val = ARCH_CPUID_ENABLE; + + return put_user(val, (unsigned int __user *)adr); +} + +int set_cpuid_mode(struct task_struct *task, unsigned long val) +{ + /* Only disable/enable_cpuid() if it is supported on this hardware. */ + bool cpuid_fault_supported = static_cpu_has(X86_FEATURE_CPUID_FAULT); + + if (val == ARCH_CPUID_ENABLE && cpuid_fault_supported) { + if (task_no_new_privs(task) && test_thread_flag(TIF_NOCPUID)) + return -EACCES; + + enable_cpuid(); + } else if (val == ARCH_CPUID_SIGSEGV && cpuid_fault_supported) { + disable_cpuid(); + } else { + return -EINVAL; + } + + return 0; +} + void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p, struct tss_struct *tss) { @@ -212,6 +275,15 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p, update_debugctlmsr(debugctl); } + if (test_tsk_thread_flag(prev_p, TIF_NOCPUID) ^ + test_tsk_thread_flag(next_p, TIF_NOCPUID)) { + /* prev and next are different */ + if (test_tsk_thread_flag(next_p, TIF_NOCPUID)) + switch_cpuid_faulting(true); + else + switch_cpuid_faulting(false); + } + if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^ test_tsk_thread_flag(next_p, TIF_NOTSC)) { /* prev and next are different */ @@ -635,6 +707,15 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long arg2) break; } #endif + case ARCH_GET_CPUID: { + ret = get_cpuid_mode(arg2); + break; + } + case ARCH_SET_CPUID: { + ret = set_cpuid_mode(task, arg2); + break; + } + default: ret = -EINVAL; break; diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile index 4f747ee..fbf34d3 100644 --- a/tools/testing/selftests/x86/Makefile +++ b/tools/testing/selftests/x86/Makefile @@ -5,7 +5,7 @@ include ../lib.mk .PHONY: all all_32 all_64 warn_32bit_failure clean TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall test_mremap_vdso \ - check_initial_reg_state sigreturn ldt_gdt iopl mpx-mini-test + check_initial_reg_state sigreturn ldt_gdt iopl mpx-mini-test cpuid-fault TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \ test_FCMOV test_FCOMI test_FISTTP \ vdso_restorer diff --git a/tools/testing/selftests/x86/cpuid-fault.c b/tools/testing/selftests/x86/cpuid-fault.c new file mode 100644 index 0000000..d72b723 --- /dev/null +++ b/tools/testing/selftests/x86/cpuid-fault.c @@ -0,0 +1,223 @@ + +/* + * Tests for arch_prctl(ARCH_GET_CPUID, ...) / prctl(ARCH_SET_CPUID, ...) + * + * Basic test to test behaviour of ARCH_GET_CPUID and ARCH_SET_CPUID + */ + +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +#include <signal.h> +#include <inttypes.h> +#include <cpuid.h> +#include <errno.h> +#include <sys/wait.h> + +#include <sys/prctl.h> +#include <linux/prctl.h> + +const char *cpuid_names[] = { + [0] = "[not set]", + [ARCH_CPUID_ENABLE] = "ARCH_CPUID_ENABLE", + [ARCH_CPUID_SIGSEGV] = "ARCH_CPUID_SIGSEGV", +}; + +int arch_prctl(int code, unsigned long arg2) +{ + return syscall(SYS_arch_prctl, code, arg2); +} + +int cpuid(unsigned int *eax, unsigned int *ebx, unsigned int *ecx, + unsigned int *edx) +{ + return __get_cpuid(0, eax, ebx, ecx, edx); +} + +int do_child_exec_test(int eax, int ebx, int ecx, int edx) +{i + int cpuid_val = 0, child = 0, status = 0; + + printf("arch_prctl(ARCH_GET_CPUID, &cpuid_val); "); + fflush(stdout); + + if (arch_prctl(ARCH_GET_CPUID, (unsigned long)&cpuid_val) != 0) + exit(42); + + printf("cpuid_val == %s\n", cpuid_names[cpuid_val]); + if (cpuid_val != ARCH_CPUID_SIGSEGV) + exit(42); + + if ((child = fork()) == 0) + execl("/proc/self/exe", "cpuid-fault", NULL); + + /* That will blow up almost immediately, since dl/libc use cpuid. */ + if (child != waitpid(child, &status, 0)) + exit(42); + + if (!WIFSIGNALED(status) || WTERMSIG(status) != SIGSEGV) + exit(42); + + return 0; +} + +int child_received_signal; + +void child_sigsegv_cb(int sig) +{ + int cpuid_val = 0; + + child_received_signal = 1; + printf("[ SIG_SEGV ]\n"); + printf("arch_prctl(ARCH_GET_CPUID, &cpuid_val); "); + fflush(stdout); + + if (arch_prctl(ARCH_GET_CPUID, (unsigned long)&cpuid_val) != 0) + exit(42); + + printf("cpuid_val == %s\n", cpuid_names[cpuid_val]); + printf("arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_ENABLE)\n"); + fflush(stdout); + if (arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_ENABLE) != 0) + exit(errno); + + printf("cpuid() == "); +} + +int do_child_test(void) +{ + unsigned int eax = 0, ebx = 0, ecx = 0, edx = 0; + + signal(SIGSEGV, child_sigsegv_cb); + + /* the child starts out with cpuid disabled, the signal handler + * attempts to enable and retry + */ + printf("cpuid() == "); + fflush(stdout); + cpuid(&eax, &ebx, &ecx, &edx); + printf("{%x, %x, %x, %x}\n", eax, ebx, ecx, edx); + return child_received_signal ? 0 : 42; +} + +void sigsegv_cb(int sig) +{ + int cpuid_val = 0; + + printf("[ SIG_SEGV ]\n"); + printf("arch_prctl(ARCH_GET_CPUID, &cpuid_val); "); + fflush(stdout); + + if (arch_prctl(ARCH_GET_CPUID, (unsigned long)&cpuid_val) != 0) + exit(42); + + printf("cpuid_val == %s\n", cpuid_names[cpuid_val]); + printf("arch_prctl(ARC_SET_CPUID, ARCH_CPUID_ENABLE)\n"); + fflush(stdout); + if (arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_ENABLE) != 0) + exit(42); + + printf("cpuid() == "); +} + +int main(void) +{ + int cpuid_val = 0, child = 0, status = 0; + unsigned int eax = 0, ebx = 0, ecx = 0, edx = 0; + + signal(SIGSEGV, sigsegv_cb); + + cpuid(&eax, &ebx, &ecx, &edx); + printf("cpuid() == {%x, %x, %x, %x}\n", eax, ebx, ecx, edx); + printf("arch_prctl(ARCH_GET_CPUID, &cpuid_val); "); + fflush(stdout); + + if (arch_prctl(ARCH_GET_CPUID, (unsigned long)&cpuid_val) != 0) { + if (errno == EINVAL) { + printf("ARCH_GET_CPUID is unsupported on this system."); + fflush(stdout); + exit(0); /* no ARCH_GET_CPUID on this system */ + } else { + exit(42); + } + } + + printf("cpuid_val == %s\n", cpuid_names[cpuid_val]); + cpuid(&eax, &ebx, &ecx, &edx); + printf("cpuid() == {%x, %x, %x, %x}\n", eax, ebx, ecx, edx); + printf("arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_ENABLE)\n"); + fflush(stdout); + + if (arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_ENABLE) != 0) { + if (errno == EINVAL) { + printf("ARCH_SET_CPUID is unsupported on this system."); + fflush(stdout); + exit(0); /* no ARCH_SET_CPUID on this system */ + } else { + exit(42); + } + } + + + cpuid(&eax, &ebx, &ecx, &edx); + printf("cpuid() == {%x, %x, %x, %x}\n", eax, ebx, ecx, edx); + printf("arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_SIGSEGV)\n"); + fflush(stdout); + + if (arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_SIGSEGV) == -1) + exit(42); + + printf("cpuid() == "); + fflush(stdout); + eax = ebx = ecx = edx = 0; + cpuid(&eax, &ebx, &ecx, &edx); + printf("{%x, %x, %x, %x}\n", eax, ebx, ecx, edx); + printf("arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_SIGSEGV)\n"); + fflush(stdout); + + if (arch_prctl(ARCH_SET_CPUID, ARCH_CPUID_SIGSEGV) == -1) + exit(42); + + printf("do_child_test\n"); + fflush(stdout); + if ((child = fork()) == 0) + return do_child_test(); + + if (child != waitpid(child, &status, 0)) + exit(42); + + if (WEXITSTATUS(status) != 0) + exit(42); + + printf("prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)\n"); + fflush(stdout); + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) != 0) + exit(42); + + printf("do_child_test\n"); + fflush(stdout); + if ((child = fork()) == 0) + return do_child_test(); + + if (child != waitpid(child, &status, 0)) + exit(42); + + if (WEXITSTATUS(status) != EACCES) + exit(42); + + printf("do_child_exec_test\n"); + fflush(stdout); + if ((child = fork()) == 0) + return do_child_exec_test(eax, ebx, ecx, edx); + + if (child != waitpid(child, &status, 0)) + exit(42); + + if (WEXITSTATUS(status) != 0) + exit(42); + + printf("All tests passed!\n"); + fflush(stdout); + exit(EXIT_SUCCESS); +} + -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
