This patch adds the PR_MPX_REGISTER and PR_MPX_UNREGISTER prctl()
commands. These commands can be used to register and unregister MPX
related resource on the x86 platform.
The base of the bounds directory is set into mm_struct during
PR_MPX_REGISTER command execution. This member can be used to
check whether one application is mpx enabled.
Signed-off-by: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
---
arch/x86/include/asm/mpx.h | 1 +
arch/x86/include/asm/processor.h | 18 ++++++++++++
arch/x86/kernel/mpx.c | 56 ++++++++++++++++++++++++++++++++++++++
include/linux/mm_types.h | 3 ++
include/uapi/linux/prctl.h | 6 ++++
kernel/sys.c | 12 ++++++++
6 files changed, 96 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h
index 780af63..6cb0853 100644
--- a/arch/x86/include/asm/mpx.h
+++ b/arch/x86/include/asm/mpx.h
@@ -43,6 +43,7 @@
#define MPX_BT_SIZE_BYTES (1UL<<(MPX_BT_ENTRY_OFFSET+MPX_BT_ENTRY_SHIFT))
#define MPX_BNDSTA_ERROR_CODE 0x3
+#define MPX_BNDCFG_ENABLE_FLAG 0x1
#define MPX_BD_ENTRY_VALID_FLAG 0x1
struct mpx_insn {
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a4ea023..6e0966e 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -952,6 +952,24 @@ extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
extern int get_tsc_mode(unsigned long adr);
extern int set_tsc_mode(unsigned int val);
+/* Register/unregister a process' MPX related resource */
+#define MPX_REGISTER(tsk) mpx_register((tsk))
+#define MPX_UNREGISTER(tsk) mpx_unregister((tsk))
+
+#ifdef CONFIG_X86_INTEL_MPX
+extern int mpx_register(struct task_struct *tsk);
+extern int mpx_unregister(struct task_struct *tsk);
+#else
+static inline int mpx_register(struct task_struct *tsk)
+{
+ return -EINVAL;
+}
+static inline int mpx_unregister(struct task_struct *tsk)
+{
+ return -EINVAL;
+}
+#endif /* CONFIG_X86_INTEL_MPX */
+
extern u16 amd_get_nb_id(int cpu);
static inline uint32_t hypervisor_cpuid_base(const char *sig, uint32_t leaves)
diff --git a/arch/x86/kernel/mpx.c b/arch/x86/kernel/mpx.c
index c1957a8..6b7e526 100644
--- a/arch/x86/kernel/mpx.c
+++ b/arch/x86/kernel/mpx.c
@@ -1,6 +1,62 @@
#include <linux/kernel.h>
#include <linux/syscalls.h>
+#include <linux/prctl.h>
#include <asm/mpx.h>
+#include <asm/i387.h>
+#include <asm/fpu-internal.h>
+
+/*
+ * This should only be called when cpuid has been checked
+ * and we are sure that MPX is available.
+ */
+static __user void *task_get_bounds_dir(struct task_struct *tsk)
+{
+ struct xsave_struct *xsave_buf;
+
+ fpu_xsave(&tsk->thread.fpu);
+ xsave_buf = &(tsk->thread.fpu.state->xsave);
+ if (!(xsave_buf->bndcsr.cfg_reg_u & MPX_BNDCFG_ENABLE_FLAG))
+ return NULL;
+
+ return (void __user *)(unsigned long)(xsave_buf->bndcsr.cfg_reg_u &
+ MPX_BNDCFG_ADDR_MASK);
+}
+
+int mpx_register(struct task_struct *tsk)
+{
+ struct mm_struct *mm = tsk->mm;
+
+ if (!cpu_has_mpx)
+ return -EINVAL;
+
+ /*
+ * runtime in the userspace will be responsible for allocation of
+ * the bounds directory. Then, it will save the base of the bounds
+ * directory into XSAVE/XRSTOR Save Area and enable MPX through
+ * XRSTOR instruction.
+ *
+ * fpu_xsave() is expected to be very expensive. In order to do
+ * performance optimization, here we get the base of the bounds
+ * directory and then save it into mm_struct to be used in future.
+ */
+ mm->bd_addr = task_get_bounds_dir(tsk);
+ if (!mm->bd_addr)
+ return -EINVAL;
+
+ pr_debug("MPX BD base address %p\n", mm->bd_addr);
+ return 0;
+}
+
+int mpx_unregister(struct task_struct *tsk)
+{
+ struct mm_struct *mm = current->mm;
+
+ if (!cpu_has_mpx)
+ return -EINVAL;
+
+ mm->bd_addr = NULL;
+ return 0;
+}
enum reg_type {
REG_TYPE_RM = 0,
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 96c5750..131b5b3 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -454,6 +454,9 @@ struct mm_struct {
bool tlb_flush_pending;
#endif
struct uprobes_state uprobes_state;
+#ifdef CONFIG_X86_INTEL_MPX
+ void __user *bd_addr; /* address of the bounds directory */
+#endif
};
static inline void mm_init_cpumask(struct mm_struct *mm)
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 58afc04..ce86fa9 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -152,4 +152,10 @@
#define PR_SET_THP_DISABLE 41
#define PR_GET_THP_DISABLE 42
+/*
+ * Register/unregister MPX related resource.
+ */
+#define PR_MPX_REGISTER 43
+#define PR_MPX_UNREGISTER 44
+
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 66a751e..eadff9c 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -91,6 +91,12 @@
#ifndef SET_TSC_CTL
# define SET_TSC_CTL(a) (-EINVAL)
#endif
+#ifndef MPX_REGISTER
+# define MPX_REGISTER(a) (-EINVAL)
+#endif
+#ifndef MPX_UNREGISTER
+# define MPX_UNREGISTER(a) (-EINVAL)
+#endif
/*
* this is where the system-wide overflow UID and GID are defined, for
@@ -2011,6 +2017,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
me->mm->def_flags &= ~VM_NOHUGEPAGE;
up_write(&me->mm->mmap_sem);
break;
+ case PR_MPX_REGISTER:
+ error = MPX_REGISTER(me);
+ break;
+ case PR_MPX_UNREGISTER:
+ error = MPX_UNREGISTER(me);
+ break;
default:
error = -EINVAL;
break;
--
1.7.1
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