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Subject[PATCH 14/19] x86, mpx: new directory entry to addr helper
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From: Dave Hansen <dave.hansen@linux.intel.com>

Currently, to get from a bounds directory entry to the virtual
address of a bounds table, we simply mask off a few low bits.
However, the set of bits we mask off is different for 32 and
64-bit binaries.

This breaks the operation out in to a helper function and also
adds a temporary variable to store the result until we are
sure we are returning one.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

---

b/arch/x86/include/asm/mpx.h | 1 -
b/arch/x86/mm/mpx.c | 41 ++++++++++++++++++++++++++++++++++-------
2 files changed, 34 insertions(+), 8 deletions(-)

diff -puN arch/x86/include/asm/mpx.h~mpx-new-entry-to-addr-helper arch/x86/include/asm/mpx.h
--- a/arch/x86/include/asm/mpx.h~mpx-new-entry-to-addr-helper 2015-05-27 09:32:19.976690756 -0700
+++ b/arch/x86/include/asm/mpx.h 2015-05-27 09:32:19.981690981 -0700
@@ -45,7 +45,6 @@
#define MPX_BNDSTA_TAIL 2
#define MPX_BNDCFG_TAIL 12
#define MPX_BNDSTA_ADDR_MASK (~((1UL<<MPX_BNDSTA_TAIL)-1))
-#define MPX_BT_ADDR_MASK (~((1UL<<MPX_BD_ENTRY_TAIL)-1))

#define MPX_BNDCFG_ADDR_MASK (~((1UL<<MPX_BNDCFG_TAIL)-1))
#define MPX_BNDSTA_ERROR_CODE 0x3
diff -puN arch/x86/mm/mpx.c~mpx-new-entry-to-addr-helper arch/x86/mm/mpx.c
--- a/arch/x86/mm/mpx.c~mpx-new-entry-to-addr-helper 2015-05-27 09:32:19.978690846 -0700
+++ b/arch/x86/mm/mpx.c 2015-05-27 09:32:19.982691026 -0700
@@ -576,29 +576,55 @@ static int mpx_resolve_fault(long __user
return 0;
}

+static unsigned long mpx_bd_entry_to_bt_addr(struct mm_struct *mm,
+ unsigned long bd_entry)
+{
+ unsigned long bt_addr = bd_entry;
+ int align_to_bytes;
+ /*
+ * Bit 0 in a bt_entry is always the valid bit.
+ */
+ bt_addr &= ~MPX_BD_ENTRY_VALID_FLAG;
+ /*
+ * Tables are naturally aligned at 8-byte boundaries
+ * on 64-bit and 4-byte boundaries on 32-bit. The
+ * documentation makes it appear that the low bits
+ * are ignored by the hardware, so we do the same.
+ */
+ if (is_64bit_mm(mm))
+ align_to_bytes = 8;
+ else
+ align_to_bytes = 4;
+ bt_addr &= ~(align_to_bytes-1);
+ return bt_addr;
+}
+
/*
* Get the base of bounds tables pointed by specific bounds
* directory entry.
*/
static int get_bt_addr(struct mm_struct *mm,
- long __user *bd_entry, unsigned long *bt_addr)
+ long __user *bd_entry_ptr,
+ unsigned long *bt_addr_result)
{
int ret;
int valid_bit;
+ unsigned long bd_entry;
+ unsigned long bt_addr;

- if (!access_ok(VERIFY_READ, (bd_entry), sizeof(*bd_entry)))
+ if (!access_ok(VERIFY_READ, (bd_entry_ptr), sizeof(*bd_entry_ptr)))
return -EFAULT;

while (1) {
int need_write = 0;

pagefault_disable();
- ret = get_user(*bt_addr, bd_entry);
+ ret = get_user(bd_entry, bd_entry_ptr);
pagefault_enable();
if (!ret)
break;
if (ret == -EFAULT)
- ret = mpx_resolve_fault(bd_entry, need_write);
+ ret = mpx_resolve_fault(bd_entry_ptr, need_write);
/*
* If we could not resolve the fault, consider it
* userspace's fault and error out.
@@ -607,8 +633,8 @@ static int get_bt_addr(struct mm_struct
return ret;
}

- valid_bit = *bt_addr & MPX_BD_ENTRY_VALID_FLAG;
- *bt_addr &= MPX_BT_ADDR_MASK;
+ valid_bit = bd_entry & MPX_BD_ENTRY_VALID_FLAG;
+ bt_addr = mpx_bd_entry_to_bt_addr(mm, bd_entry);

/*
* When the kernel is managing bounds tables, a bounds directory
@@ -617,7 +643,7 @@ static int get_bt_addr(struct mm_struct
* data in the address field, we know something is wrong. This
* -EINVAL return will cause a SIGSEGV.
*/
- if (!valid_bit && *bt_addr)
+ if (!valid_bit && bt_addr)
return -EINVAL;
/*
* Do we have an completely zeroed bt entry? That is OK. It
@@ -628,6 +654,7 @@ static int get_bt_addr(struct mm_struct
if (!valid_bit)
return -ENOENT;

+ *bt_addr_result = bt_addr;
return 0;
}

_

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