Commit f3119b83 authored Nov 11, 2015 by Dave Hansen Committed by Ingo Molnar Nov 12, 2015

x86/mpx: Fix 32-bit address space calculation



I received a bug report that running 32-bit MPX binaries on
64-bit kernels was broken.  I traced it down to this little code
snippet.  We were switching our "number of bounds directory
entries" calculation correctly.  But, we didn't switch the other
side of the calculation: the virtual space size.

This meant that we were calculating an absurd size for
bd_entry_virt_space() on 32-bit because we used the 64-bit
virt_space.

This was _also_ broken for 32-bit kernels running on 64-bit
hardware since boot_cpu_data.x86_virt_bits=48 even when running
in 32-bit mode.

Correct that and properly handle all 3 possible cases:

 1. 32-bit binary on 64-bit kernel
 2. 64-bit binary on 64-bit kernel
 3. 32-bit binary on 32-bit kernel

This manifested in having bounds tables not properly unmapped.
It "leaked" memory but had no functional impact otherwise.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20151111181934.FA7FAC34@viggo.jf.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 46561c39

arch/x86/mm/mpx.c

+17 −5

Original line number	Diff line number	Diff line
		@@ -723,11 +723,23 @@ static unsigned long mpx_get_bt_entry_offset_bytes(struct mm_struct *mm,
		*/
		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))
		unsigned long long virt_space;
		unsigned long long GB = (1ULL << 30);

		/*
		* This covers 32-bit emulation as well as 32-bit kernels
		* running on 64-bit harware.
		*/
		if (!is_64bit_mm(mm))
		return (4ULL * GB) / MPX_BD_NR_ENTRIES_32;

		/*
		* 'x86_virt_bits' returns what the hardware is capable
		* of, and returns the full >32-bit adddress space when
		* running 32-bit kernels on 64-bit hardware.
		*/
		virt_space = (1ULL << boot_cpu_data.x86_virt_bits);
		return virt_space / MPX_BD_NR_ENTRIES_64;
		else
		return virt_space / MPX_BD_NR_ENTRIES_32;
		}

		/*

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