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x86/mpx: Add temporary variable to reduce masking

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When we allocate a bounds table, we call mmap(), then add a
"valid" bit to the value before storing it in to the bounds
directory.

If we fail along the way, we go and mask that valid bit
_back_ out.  That seems a little silly, and this makes it
much more clear when we have a plain address versus an
actual table _entry_.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150607183704.3D69D5F4@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dave Hansen 2015-06-07 11:37:04 -07:00 committed by Ingo Molnar
parent b0e9b09b3b
commit a1149fc83a
1 changed files with 4 additions and 3 deletions
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7
arch/x86/mm/mpx.c
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@ -429,6 +429,7 @@ static int allocate_bt(long __user *bd_entry)
unsigned long expected_old_val = 0; unsigned long expected_old_val = 0;
unsigned long actual_old_val = 0; unsigned long actual_old_val = 0;
unsigned long bt_addr; unsigned long bt_addr;
unsigned long bd_new_entry;
int ret = 0; int ret = 0;
/* /*
@ -441,7 +442,7 @@ static int allocate_bt(long __user *bd_entry)
/* /*
* Set the valid flag (kinda like _PAGE_PRESENT in a pte) * Set the valid flag (kinda like _PAGE_PRESENT in a pte)
*/ */
bt_addr = bt_addr | MPX_BD_ENTRY_VALID_FLAG; bd_new_entry = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
/* /*
* Go poke the address of the new bounds table in to the * Go poke the address of the new bounds table in to the
@ -455,7 +456,7 @@ static int allocate_bt(long __user *bd_entry)
* of the MPX code that have to pagefault_disable(). * of the MPX code that have to pagefault_disable().
*/ */
ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry, ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
expected_old_val, bt_addr); expected_old_val, bd_new_entry);
if (ret) if (ret)
goto out_unmap; goto out_unmap;
@ -486,7 +487,7 @@ static int allocate_bt(long __user *bd_entry)
trace_mpx_new_bounds_table(bt_addr); trace_mpx_new_bounds_table(bt_addr);
return 0; return 0;
out_unmap: out_unmap:
vm_munmap(bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES); vm_munmap(bt_addr, MPX_BT_SIZE_BYTES);
return ret; return ret;
} }