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Commit a1149fc8 authored by Dave Hansen's avatar Dave Hansen Committed by Ingo Molnar
Browse files

x86/mpx: Add temporary variable to reduce masking 



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: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarThomas 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: default avatarIngo Molnar <mingo@kernel.org>
parent b0e9b09b

arch/x86/mm/mpx.c

+4 −3
Original line number Diff line number Diff line
@@ -429,6 +429,7 @@ static int allocate_bt(long __user *bd_entry) 
	unsigned long expected_old_val = 0;

	unsigned long actual_old_val = 0;

	unsigned long bt_addr;

	unsigned long bd_new_entry;

	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)

	 */

	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
@@ -455,7 +456,7 @@ static int allocate_bt(long __user *bd_entry) 
	 * of the MPX code that have to pagefault_disable().

	 */

	ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,

					   expected_old_val, bt_addr);

					   expected_old_val, bd_new_entry);

	if (ret)

		goto out_unmap;
@@ -486,7 +487,7 @@ static int allocate_bt(long __user *bd_entry) 
	trace_mpx_new_bounds_table(bt_addr);

	return 0;

out_unmap:

	vm_munmap(bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES);

	vm_munmap(bt_addr, MPX_BT_SIZE_BYTES);

	return ret;

}