[PATCH 07/11] x86, mpx: add MPX-specific mmap interface

Dave Hansen
2014-11-14T15:18:27Z

We have chosen to perform the allocation of bounds tables in
kernel (See the patch "on-demand kernel allocation of bounds
tables") and to mark these VMAs with VM_MPX.

However, there is currently no suitable interface to actually do
this. Existing interfaces, like do_mmap_pgoff(), have no way to
set a modified ->vm_ops or ->vm_flags and don't hold mmap_sem
long enough to let a caller do it.

This patch wraps mmap_region() and hold mmap_sem long enough to
make the modifications to the VMA which we need.

Also note the 32/64-bit #ifdef in the header. We actually need
to do this at runtime eventually. But, for now, we don't support
running 32-bit binaries on 64-bit kernels. Support for this will
come in later patches.

Signed-off-by: Qiaowei Ren <qiaowei.ren@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

b/arch/x86/Kconfig | 4 ++
b/arch/x86/include/asm/mpx.h | 36 ++++++++++++++++++
b/arch/x86/mm/Makefile | 2 +
b/arch/x86/mm/mpx.c | 86 +++++++++++++++++++++++++++++++++++++++++++
4 files changed, 128 insertions(+)

diff -puN /dev/null arch/x86/include/asm/mpx.h
--- /dev/null 2014-10-10 16:10:57.316716958 -0700
+++ b/arch/x86/include/asm/mpx.h 2014-11-14 07:06:23.077645424 -0800
@@ -0,0 +1,36 @@
+#ifndef _ASM_X86_MPX_H
+#define _ASM_X86_MPX_H
+
+#include <linux/types.h>
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_X86_64
+
+/* upper 28 bits [47:20] of the virtual address in 64-bit used to
+ * index into bounds directory (BD).
+ */
+#define MPX_BD_ENTRY_OFFSET 28
+#define MPX_BD_ENTRY_SHIFT 3
+/* bits [19:3] of the virtual address in 64-bit used to index into
+ * bounds table (BT).
+ */
+#define MPX_BT_ENTRY_OFFSET 17
+#define MPX_BT_ENTRY_SHIFT 5
+#define MPX_IGN_BITS 3
+
+#else
+
+#define MPX_BD_ENTRY_OFFSET 20
+#define MPX_BD_ENTRY_SHIFT 2
+#define MPX_BT_ENTRY_OFFSET 10
+#define MPX_BT_ENTRY_SHIFT 4
+#define MPX_IGN_BITS 2
+
+#endif
+
+#define MPX_BD_SIZE_BYTES (1UL<<(MPX_BD_ENTRY_OFFSET+MPX_BD_ENTRY_SHIFT))
+#define MPX_BT_SIZE_BYTES (1UL<<(MPX_BT_ENTRY_OFFSET+MPX_BT_ENTRY_SHIFT))
+
+#define MPX_BNDSTA_ERROR_CODE 0x3
+
+#endif /* _ASM_X86_MPX_H */
diff -puN arch/x86/Kconfig~mpx-v11-add-MPX-specific-mmap-interface arch/x86/Kconfig
--- a/arch/x86/Kconfig~mpx-v11-add-MPX-specific-mmap-interface 2014-11-14 07:06:23.072645199 -0800
+++ b/arch/x86/Kconfig 2014-11-14 07:06:23.078645470 -0800
@@ -244,6 +244,10 @@ config HAVE_INTEL_TXT
def_bool y
depends on INTEL_IOMMU && ACPI

+config X86_INTEL_MPX
+ def_bool y
+ depends on CPU_SUP_INTEL
+
config X86_32_SMP
def_bool y
depends on X86_32 && SMP
diff -puN arch/x86/mm/Makefile~mpx-v11-add-MPX-specific-mmap-interface arch/x86/mm/Makefile
--- a/arch/x86/mm/Makefile~mpx-v11-add-MPX-specific-mmap-interface 2014-11-14 07:06:23.074645289 -0800
+++ b/arch/x86/mm/Makefile 2014-11-14 07:06:23.078645470 -0800
@@ -30,3 +30,5 @@ obj-$(CONFIG_ACPI_NUMA) += srat.o
obj-$(CONFIG_NUMA_EMU) += numa_emulation.o

obj-$(CONFIG_MEMTEST) += memtest.o
+
+obj-$(CONFIG_X86_INTEL_MPX) += mpx.o
diff -puN /dev/null arch/x86/mm/mpx.c
--- /dev/null 2014-10-10 16:10:57.316716958 -0700
+++ b/arch/x86/mm/mpx.c 2014-11-14 07:06:23.078645470 -0800
@@ -0,0 +1,86 @@
+/*
+ * mpx.c - Memory Protection eXtensions
+ *
+ * Copyright (c) 2014, Intel Corporation.
+ * Qiaowei Ren <qiaowei.ren@intel.com>
+ * Dave Hansen <dave.hansen@intel.com>
+ */
+#include <linux/kernel.h>
+#include <linux/syscalls.h>
+#include <linux/sched/sysctl.h>
+
+#include <asm/mman.h>
+#include <asm/mpx.h>
+
+static const char *mpx_mapping_name(struct vm_area_struct *vma)
+{
+ return "[mpx]";
+}
+
+static struct vm_operations_struct mpx_vma_ops = {
+ .name = mpx_mapping_name,
+};
+
+/*
+ * This is really a simplified "vm_mmap". it only handles MPX
+ * bounds tables (the bounds directory is user-allocated).
+ *
+ * Later on, we use the vma->vm_ops to uniquely identify these
+ * VMAs.
+ */
+static unsigned long mpx_mmap(unsigned long len)
+{
+ unsigned long ret;
+ unsigned long addr, pgoff;
+ struct mm_struct *mm = current->mm;
+ vm_flags_t vm_flags;
+ struct vm_area_struct *vma;
+
+ /* Only bounds table and bounds directory can be allocated here */
+ if (len != MPX_BD_SIZE_BYTES && len != MPX_BT_SIZE_BYTES)
+ return -EINVAL;
+
+ down_write(&mm->mmap_sem);
+
+ /* Too many mappings? */
+ if (mm->map_count > sysctl_max_map_count) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ /* Obtain the address to map to. we verify (or select) it and ensure
+ * that it represents a valid section of the address space.
+ */
+ addr = get_unmapped_area(NULL, 0, len, 0, MAP_ANONYMOUS | MAP_PRIVATE);
+ if (addr & ~PAGE_MASK) {
+ ret = addr;
+ goto out;
+ }
+
+ vm_flags = VM_READ | VM_WRITE | VM_MPX |
+ mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+
+ /* Set pgoff according to addr for anon_vma */
+ pgoff = addr >> PAGE_SHIFT;
+
+ ret = mmap_region(NULL, addr, len, vm_flags, pgoff);
+ if (IS_ERR_VALUE(ret))
+ goto out;
+
+ vma = find_vma(mm, ret);
+ if (!vma) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ vma->vm_ops = &mpx_vma_ops;
+
+ if (vm_flags & VM_LOCKED) {
+ up_write(&mm->mmap_sem);
+ mm_populate(ret, len);
+ return ret;
+ }
+
+out:
+ up_write(&mm->mmap_sem);
+ return ret;
+}
_