x86, mpx: fix 32-bit address space calculation
From: Dave Hansen <dave.hansen@linux.intel.com>
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>
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 2cf09ca..0ef4c60 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -719,11 +719,23 @@
*/
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;
+ 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;
}
/*
