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 <kh...@kylehuey.com>
---
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
