linux-kernel - [PATCH] [URGENT] x86, fpu: fix double-increment in setup_xstate

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Date:	Thu, 11 Jun 2015 12:34:00 -0700
From:	Dave Hansen <dave@...1.net>
To:	dave@...1.net
Cc:	dave.hansen@...ux.intel.com, mingo@...nel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [PATCH] [URGENT] x86, fpu: fix double-increment in setup_xstate_features()


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

I noticed that my MPX tracepoints were producing garbage for the
lower and upper bounds:

	mpx_bounds_register_exception: address referenced: 0x00007fffffffccb7 bounds: lower: 0x0 ~upper: 0xffffffffffffffff
	mpx_bounds_register_exception: address referenced: 0x00007fffffffccbf bounds: lower: 0x0 ~upper: 0xffffffffffffffff

This is, of course, bogus because 0x00007fffffffccbf is *within*
the bounds.  I assumed that my instruction decoder was bad and
went looking at it.  But I eventually realized that I was getting
a '0' offset back from xstate_offsets[BNDREGS].

It was being skipped in the initialization, which is obviously
bogus, so remove the extra leaf++.

This also goes an initializes xstate_offsets/sizes[] to -1 so
so that bugs like this will oops instead of silently failing
in interesting ways.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org
Cc: x86@...nel.org

--

Note: this applies on top of tip/x86/fpu, which is currently:

	97ac46a x86/mpx: Allow 32-bit binaries on 64-bit kernels again

This was introduced by:

	39f1acd x86/fpu/xstate: Don't assume the first zero xfeatures zero bit means the end

---

 b/arch/x86/kernel/fpu/xstate.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -puN arch/x86/kernel/fpu/xstate.c~x86-fpu-xstate-fix-double-leaf-increment arch/x86/kernel/fpu/xstate.c
--- a/arch/x86/kernel/fpu/xstate.c~x86-fpu-xstate-fix-double-leaf-increment	2015-06-11 11:25:42.706604347 -0700
+++ b/arch/x86/kernel/fpu/xstate.c	2015-06-11 11:38:45.271899550 -0700
@@ -31,7 +31,8 @@ static const char *xfeature_names[] =
  */
 u64 xfeatures_mask __read_mostly;
 
-static unsigned int xstate_offsets[XFEATURES_NR_MAX], xstate_sizes[XFEATURES_NR_MAX];
+static unsigned int xstate_offsets[XFEATURES_NR_MAX] = { [ 0 ... XFEATURES_NR_MAX - 1] = -1};
+static unsigned int xstate_sizes[XFEATURES_NR_MAX]   = { [ 0 ... XFEATURES_NR_MAX - 1] = -1};
 static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];
 
 /* The number of supported xfeatures in xfeatures_mask: */
@@ -187,7 +188,6 @@ static void __init setup_xstate_features
 		xstate_sizes[leaf] = eax;
 
 		printk(KERN_INFO "x86/fpu: xstate_offset[%d]: %04x, xstate_sizes[%d]: %04x\n", leaf, ebx, leaf, eax);
-		leaf++;
 	}
 }
 
_
--
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