linux-kernel - [PATCH 4.2 062/124] x86/mpx: Fix 32-bit address space calculation

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Message-Id: <20151207144922.747704927@linuxfoundation.org>
Date:	Mon,  7 Dec 2015 09:55:52 -0500
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>, Dave Hansen <dave@...1.net>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.2 062/124] x86/mpx: Fix 32-bit address space calculation

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Hansen <dave.hansen@...ux.intel.com>

commit f3119b830264d89d216bfb378ab65065dffa02d9 upstream.

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@...ux.intel.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave@...1.net>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20151111181934.FA7FAC34@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/mm/mpx.c |   22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -759,11 +759,23 @@ static unsigned long mpx_get_bt_entry_of
  */
 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;
 }

 /*

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