[PATCH 16/19] x86, mpx: support 32-bit binaries on 64-bit kernel

Dave Hansen
2015-06-07T18:39:06Z

From: Dave Hansen <dave.hansen@linux.intel.com>

Right now, the kernel can only switch between 64-bit and 32-bit
binaries at compile time. This patch adds support for 32-bit
binaries on 64-bit kernels when we support ia32 emulation.

We essentially choose which set of table sizes to use when doing
arithmetic for the bounds table calculations.

This also uses a different approach for calculating the table
indexes than before. I think the new one makes it much more
clear what is going on, and allows us to share more code between
the 32 and 64-bit cases.

Based-on-patch-by: Qiaowei Ren <qiaowei.ren@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

--

Changes from v22:
* fix spelling nit

Changes from v21:
* remove old comment
* add a comment about why the masks are OK
* use cpu_info->x86_virt_bits
* add comment about lack of 32-bit hole

Changes from v20:

* Fix macro confusion between BD and BT
* Add accessor for bt_entry_size_bytes()

---

b/arch/x86/include/asm/mpx.h | 66 ++++++++--------
b/arch/x86/mm/mpx.c | 170 +++++++++++++++++++++++++++++++++++++------
2 files changed, 181 insertions(+), 55 deletions(-)

diff -puN arch/x86/include/asm/mpx.h~0002-x86-mpx-support-32bit-binaries-on-64bit-kernel arch/x86/include/asm/mpx.h
--- a/arch/x86/include/asm/mpx.h~0002-x86-mpx-support-32bit-binaries-on-64bit-kernel 2015-06-01 10:24:09.323960764 -0700
+++ b/arch/x86/include/asm/mpx.h 2015-06-01 10:24:09.329961034 -0700
@@ -13,49 +13,47 @@
#define MPX_BNDCFG_ENABLE_FLAG 0x1
#define MPX_BD_ENTRY_VALID_FLAG 0x1

-#ifdef CONFIG_X86_64
-
-/* upper 28 bits [47:20] of the virtual address in 64-bit used to
- * index into bounds directory (BD).
+/*
+ * The upper 28 bits [47:20] of the virtual address in 64-bit
+ * are used to index into bounds directory (BD).
+ *
+ * The directory is 2G (2^31) in size, and with 8-byte entries
+ * it has 2^28 entries.
*/
-#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_BD_SIZE_BYTES_64 (1UL<<31)
+#define MPX_BD_ENTRY_BYTES_64 8
+#define MPX_BD_NR_ENTRIES_64 (MPX_BD_SIZE_BYTES_64/MPX_BD_ENTRY_BYTES_64)
+
+/*
+ * The 32-bit directory is 4MB (2^22) in size, and with 4-byte
+ * entries it has 2^20 entries.
*/
-#define MPX_BT_ENTRY_OFFSET 17
-#define MPX_BT_ENTRY_SHIFT 5
-#define MPX_IGN_BITS 3
-#define MPX_BD_ENTRY_TAIL 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
-#define MPX_BD_ENTRY_TAIL 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_BD_SIZE_BYTES_32 (1UL<<22)
+#define MPX_BD_ENTRY_BYTES_32 4
+#define MPX_BD_NR_ENTRIES_32 (MPX_BD_SIZE_BYTES_32/MPX_BD_ENTRY_BYTES_32)
+
+/*
+ * A 64-bit table is 4MB total in size, and an entry is
+ * 4 64-bit pointers in size.
+ */
+#define MPX_BT_SIZE_BYTES_64 (1UL<<22)
+#define MPX_BT_ENTRY_BYTES_64 32
+#define MPX_BT_NR_ENTRIES_64 (MPX_BT_SIZE_BYTES_64/MPX_BT_ENTRY_BYTES_64)
+
+/*
+ * A 32-bit table is 16kB total in size, and an entry is
+ * 4 32-bit pointers in size.
+ */
+#define MPX_BT_SIZE_BYTES_32 (1UL<<14)
+#define MPX_BT_ENTRY_BYTES_32 16
+#define MPX_BT_NR_ENTRIES_32 (MPX_BT_SIZE_BYTES_32/MPX_BT_ENTRY_BYTES_32)

#define MPX_BNDSTA_TAIL 2
#define MPX_BNDCFG_TAIL 12
#define MPX_BNDSTA_ADDR_MASK (~((1UL<<MPX_BNDSTA_TAIL)-1))
-
#define MPX_BNDCFG_ADDR_MASK (~((1UL<<MPX_BNDCFG_TAIL)-1))
#define MPX_BNDSTA_ERROR_CODE 0x3

-#define MPX_BD_ENTRY_MASK ((1<<MPX_BD_ENTRY_OFFSET)-1)
-#define MPX_BT_ENTRY_MASK ((1<<MPX_BT_ENTRY_OFFSET)-1)
-#define MPX_GET_BD_ENTRY_OFFSET(addr) ((((addr)>>(MPX_BT_ENTRY_OFFSET+ \
- MPX_IGN_BITS)) & MPX_BD_ENTRY_MASK) << MPX_BD_ENTRY_SHIFT)
-#define MPX_GET_BT_ENTRY_OFFSET(addr) ((((addr)>>MPX_IGN_BITS) & \
- MPX_BT_ENTRY_MASK) << MPX_BT_ENTRY_SHIFT)
-
#ifdef CONFIG_X86_INTEL_MPX
siginfo_t *mpx_generate_siginfo(struct pt_regs *regs);
int mpx_handle_bd_fault(void);
diff -puN arch/x86/mm/mpx.c~0002-x86-mpx-support-32bit-binaries-on-64bit-kernel arch/x86/mm/mpx.c
--- a/arch/x86/mm/mpx.c~0002-x86-mpx-support-32bit-binaries-on-64bit-kernel 2015-06-01 10:24:09.325960854 -0700
+++ b/arch/x86/mm/mpx.c 2015-06-01 10:24:09.330961080 -0700
@@ -34,6 +34,22 @@ static int is_mpx_vma(struct vm_area_str
return (vma->vm_ops == &mpx_vma_ops);
}

+static inline unsigned long mpx_bd_size_bytes(struct mm_struct *mm)
+{
+ if (is_64bit_mm(mm))
+ return MPX_BD_SIZE_BYTES_64;
+ else
+ return MPX_BD_SIZE_BYTES_32;
+}
+
+static inline unsigned long mpx_bt_size_bytes(struct mm_struct *mm)
+{
+ if (is_64bit_mm(mm))
+ return MPX_BT_SIZE_BYTES_64;
+ else
+ return MPX_BT_SIZE_BYTES_32;
+}
+
/*
* This is really a simplified "vm_mmap". it only handles MPX
* bounds tables (the bounds directory is user-allocated).
@@ -50,7 +66,7 @@ static unsigned long mpx_mmap(unsigned l
struct vm_area_struct *vma;

/* Only bounds table can be allocated here */
- if (len != MPX_BT_SIZE_BYTES)
+ if (len != mpx_bt_size_bytes(mm))
return -EINVAL;

down_write(&mm->mmap_sem);
@@ -449,13 +465,12 @@ static int mpx_cmpxchg_bd_entry(struct m
}

/*
- * With 32-bit mode, MPX_BT_SIZE_BYTES is 4MB, and the size of each
- * bounds table is 16KB. With 64-bit mode, MPX_BT_SIZE_BYTES is 2GB,
+ * With 32-bit mode, a bounds directory is 4MB, and the size of each
+ * bounds table is 16KB. With 64-bit mode, a bounds directory is 2GB,
* and the size of each bounds table is 4MB.
*/
-static int allocate_bt(long __user *bd_entry)
+static int allocate_bt(struct mm_struct *mm, long __user *bd_entry)
{
- struct mm_struct *mm = current->mm;
unsigned long expected_old_val = 0;
unsigned long actual_old_val = 0;
unsigned long bt_addr;
@@ -466,7 +481,7 @@ static int allocate_bt(long __user *bd_e
* Carve the virtual space out of userspace for the new
* bounds table:
*/
- bt_addr = mpx_mmap(MPX_BT_SIZE_BYTES);
+ bt_addr = mpx_mmap(mpx_bt_size_bytes(mm));
if (IS_ERR((void *)bt_addr))
return PTR_ERR((void *)bt_addr);
/*
@@ -517,7 +532,7 @@ static int allocate_bt(long __user *bd_e
trace_mpx_new_bounds_table(bt_addr);
return 0;
out_unmap:
- vm_munmap(bt_addr, MPX_BT_SIZE_BYTES);
+ vm_munmap(bt_addr, mpx_bt_size_bytes(mm));
return ret;
}

@@ -536,6 +551,7 @@ static int do_mpx_bt_fault(void)
{
unsigned long bd_entry, bd_base;
const struct bndcsr *bndcsr;
+ struct mm_struct *mm = current->mm;

bndcsr = get_xsave_field_ptr(XSTATE_BNDCSR);
if (!bndcsr)
@@ -554,10 +570,10 @@ static int do_mpx_bt_fault(void)
* the directory is.
*/
if ((bd_entry < bd_base) ||
- (bd_entry >= bd_base + MPX_BD_SIZE_BYTES))
+ (bd_entry >= bd_base + mpx_bd_size_bytes(mm)))
return -EINVAL;

- return allocate_bt((long __user *)bd_entry);
+ return allocate_bt(mm, (long __user *)bd_entry);
}

int mpx_handle_bd_fault(void)
@@ -789,7 +805,115 @@ static int unmap_single_bt(struct mm_str
* avoid recursion, do_munmap() will check whether it comes
* from one bounds table through VM_MPX flag.
*/
- return do_munmap(mm, bt_addr, MPX_BT_SIZE_BYTES);
+ return do_munmap(mm, bt_addr, mpx_bt_size_bytes(mm));
+}
+
+static inline int bt_entry_size_bytes(struct mm_struct *mm)
+{
+ if (is_64bit_mm(mm))
+ return MPX_BT_ENTRY_BYTES_64;
+ else
+ return MPX_BT_ENTRY_BYTES_32;
+}
+
+/*
+ * Take a virtual address and turns it in to the offset in bytes
+ * inside of the bounds table where the bounds table entry
+ * controlling 'addr' can be found.
+ */
+static unsigned long mpx_get_bt_entry_offset_bytes(struct mm_struct *mm,
+ unsigned long addr)
+{
+ unsigned long bt_table_nr_entries;
+ unsigned long offset = addr;
+
+ if (is_64bit_mm(mm)) {
+ /* Bottom 3 bits are ignored on 64-bit */
+ offset >>= 3;
+ bt_table_nr_entries = MPX_BT_NR_ENTRIES_64;
+ } else {
+ /* Bottom 2 bits are ignored on 32-bit */
+ offset >>= 2;
+ bt_table_nr_entries = MPX_BT_NR_ENTRIES_32;
+ }
+ /*
+ * We know the size of the table in to which we are
+ * indexing, and we have eliminated all the low bits
+ * which are ignored for indexing.
+ *
+ * Mask out all the high bits which we do not need
+ * to index in to the table. Note that the tables
+ * are always powers of two so this gives us a proper
+ * mask.
+ */
+ offset &= (bt_table_nr_entries-1);
+ /*
+ * We now have an entry offset in terms of *entries* in
+ * the table. We need to scale it back up to bytes.
+ */
+ offset *= bt_entry_size_bytes(mm);
+ return offset;
+}
+
+/*
+ * How much virtual address space does a single bounds
+ * directory entry cover?
+ *
+ * Note, we need a long long because 4GB doesn't fit in
+ * to a long on 32-bit.
+ */
+static inline unsigned long bd_entry_virt_space(struct mm_struct *mm)
+{
+ unsigned long long virt_space = (1ULL << boot_cpu_data.x86_virt_bits);
+ if (is_64bit_mm(mm))
+ return virt_space / MPX_BD_NR_ENTRIES_64;
+ else
+ return virt_space / MPX_BD_NR_ENTRIES_32;
+}
+
+/*
+ * Return an offset in terms of bytes in to the bounds
+ * directory where the bounds directory entry for a given
+ * virtual address resides.
+ *
+ * This has to be in bytes because the directory entries
+ * are different sizes on 64/32 bit.
+ */
+static unsigned long mpx_get_bd_entry_offset(struct mm_struct *mm,
+ unsigned long addr)
+{
+ /*
+ * There are several ways to derive the bd offsets. We
+ * use the following approach here:
+ * 1. We know the size of the virtual address space
+ * 2. We know the number of entries in a bounds table
+ * 3. We know that each entry covers a fixed amount of
+ * virtual address space.
+ * So, we can just divide the virtual address by the
+ * virtual space used by one entry to determine which
+ * entry "controls" the given virtual address.
+ */
+ if (is_64bit_mm(mm)) {
+ int bd_entry_size = 8; /* 64-bit pointer */
+ /*
+ * Take the 64-bit addressing hole in to account.
+ */
+ addr &= ((1UL << boot_cpu_data.x86_virt_bits) - 1);
+ return (addr / bd_entry_virt_space(mm)) * bd_entry_size;
+ } else {
+ int bd_entry_size = 4; /* 32-bit pointer */
+ /*
+ * 32-bit has no hole so this case needs no mask
+ */
+ return (addr / bd_entry_virt_space(mm)) * bd_entry_size;
+ }
+ /*
+ * The two return calls above are exact copies. If we
+ * pull out a single copy and put it in here, gcc won't
+ * realize that we're doing a power-of-2 divide and use
+ * shifts. It uses a real divide. If we put them up
+ * there, it manages to figure it out (gcc 4.8.3).
+ */
}

/*
@@ -803,6 +927,7 @@ static int unmap_shared_bt(struct mm_str
unsigned long end, bool prev_shared, bool next_shared)
{
unsigned long bt_addr;
+ unsigned long start_off, end_off;
int ret;

ret = get_bt_addr(mm, bd_entry, &bt_addr);
@@ -814,17 +939,20 @@ static int unmap_shared_bt(struct mm_str
if (ret)
return ret;

+ start_off = mpx_get_bt_entry_offset_bytes(mm, start);
+ end_off = mpx_get_bt_entry_offset_bytes(mm, end);
+
if (prev_shared && next_shared)
ret = zap_bt_entries(mm, bt_addr,
- bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
- bt_addr+MPX_GET_BT_ENTRY_OFFSET(end));
+ bt_addr + start_off,
+ bt_addr + end_off);
else if (prev_shared)
ret = zap_bt_entries(mm, bt_addr,
- bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
- bt_addr+MPX_BT_SIZE_BYTES);
+ bt_addr + start_off,
+ bt_addr + mpx_bt_size_bytes(mm));
else if (next_shared)
ret = zap_bt_entries(mm, bt_addr, bt_addr,
- bt_addr+MPX_GET_BT_ENTRY_OFFSET(end));
+ bt_addr + end_off);
else
ret = unmap_single_bt(mm, bd_entry, bt_addr);

@@ -845,8 +973,8 @@ static int unmap_edge_bts(struct mm_stru
struct vm_area_struct *prev, *next;
bool prev_shared = false, next_shared = false;

- bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
- bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
+ bde_start = mm->bd_addr + mpx_get_bd_entry_offset(mm, start);
+ bde_end = mm->bd_addr + mpx_get_bd_entry_offset(mm, end-1);

/*
* Check whether bde_start and bde_end are shared with adjacent
@@ -858,10 +986,10 @@ static int unmap_edge_bts(struct mm_stru
* in to 'next'.
*/
next = find_vma_prev(mm, start, &prev);
- if (prev && (mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(prev->vm_end-1))
+ if (prev && (mm->bd_addr + mpx_get_bd_entry_offset(mm, prev->vm_end-1))
== bde_start)
prev_shared = true;
- if (next && (mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(next->vm_start))
+ if (next && (mm->bd_addr + mpx_get_bd_entry_offset(mm, next->vm_start))
== bde_end)
next_shared = true;

@@ -927,8 +1055,8 @@ static int mpx_unmap_tables(struct mm_st
* 1. fully covered
* 2. not at the edges of the mapping, even if full aligned
*/
- bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
- bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
+ bde_start = mm->bd_addr + mpx_get_bd_entry_offset(mm, start);
+ bde_end = mm->bd_addr + mpx_get_bd_entry_offset(mm, end-1);
for (bd_entry = bde_start + 1; bd_entry < bde_end; bd_entry++) {
ret = get_bt_addr(mm, bd_entry, &bt_addr);
switch (ret) {
_