linux-kernel - [PATCH 11/11] x86, fpu: check CPU-provided sizes against struct declarations

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Date:	Thu, 27 Aug 2015 10:11:11 -0700
From:	Dave Hansen <dave@...1.net>
To:	dave@...1.net
Cc:	dave.hansen@...ux.intel.com, mingo@...hat.com, x86@...nel.org,
	bp@...en8.de, fenghua.yu@...el.com, tim.c.chen@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH 11/11] x86, fpu: check CPU-provided sizes against struct declarations


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

We now have C structures defined for each of the XSAVE state
components that we support.  This patch adds checks during our
verification pass to ensure that the CPU-provided data
enumerated in CPUID leaves matches our C structures.

If not, we warn and dump all the XSAVE CPUID leaves.

Note: this *actually* found an inconsistency with the MPX
'bndcsr' state.  The hardware pads it out differently from
our C structures.  This patch caught it and warned.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: x86@...nel.org
Cc: Borislav Petkov <bp@...en8.de>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org
---

 b/arch/x86/kernel/fpu/xstate.c |   53 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff -puN arch/x86/kernel/fpu/xstate.c~x86-fpu-check-against-struct-declarations arch/x86/kernel/fpu/xstate.c
--- a/arch/x86/kernel/fpu/xstate.c~x86-fpu-check-against-struct-declarations	2015-08-27 10:08:05.023791536 -0700
+++ b/arch/x86/kernel/fpu/xstate.c	2015-08-27 10:08:05.027791718 -0700
@@ -409,6 +409,49 @@ static void __xstate_dump_leaves(void)
 	}									\
 } while (0)
 
+#define XCHECK_SZ(sz, nr, nr_macro, __struct) do {			\
+	if ((nr == nr_macro) &&						\
+	    WARN_ONCE(sz != sizeof(__struct),				\
+		"%s: struct is %ld bytes, cpu state %d bytes\n",	\
+		__stringify(nr_macro), sizeof(__struct), sz)) {		\
+		__xstate_dump_leaves();					\
+	}								\
+} while (0)
+
+/*
+ * We have a C struct for each 'xstate'.  We need to ensure
+ * that our software representation matches what the CPU
+ * tells us about the state's size.
+ */
+static void check_xstate_against_struct(int nr)
+{
+	/*
+	 * Ask the CPU for the size of the state.
+	 */
+	int sz = xfeature_size(nr);
+	/*
+	 * Match each CPU state with the corresponding software
+	 * structure.
+	 */
+	XCHECK_SZ(sz, nr, XFEATURE_NR_YMM,       struct ymmh_struct);
+	XCHECK_SZ(sz, nr, XFEATURE_NR_BNDREGS,   struct mpx_bndreg_state);
+	XCHECK_SZ(sz, nr, XFEATURE_NR_BNDCSR,    struct mpx_bndcsr_state);
+	XCHECK_SZ(sz, nr, XFEATURE_NR_OPMASK,    struct avx_512_opmask_state);
+	XCHECK_SZ(sz, nr, XFEATURE_NR_ZMM_Hi256, struct avx_512_zmm_uppers_state);
+	XCHECK_SZ(sz, nr, XFEATURE_NR_Hi16_ZMM,  struct avx_512_hi16_state);
+
+	/*
+	 * Make *SURE* to add any feature numbers in below if
+	 * there are "holes" in the xsave state component
+	 * numbers.
+	 */
+	if ((nr < XFEATURE_NR_YMM) ||
+	    (nr >= XFEATURES_NR_MAX)) {
+		WARN_ONCE(1, "no structure for xstate: %d\n", nr);
+		XSTATE_WARN_ON(1);
+	}
+}
+
 /*
  * This essentially double-checks what the cpu told us about
  * how large the XSAVE buffer needs to be.  We are recalculating
@@ -422,6 +465,8 @@ static void do_extra_xstate_size_checks(
 	for (i = FIRST_EXTENDED_XFEATURE_NR; i < XFEATURES_NR_MAX; i++) {
 		if (!xfeature_nr_enabled(i))
 			continue;
+
+		check_xstate_against_struct(i);
 		/*
 		 * Supervisor state components can be managed only by
 		 * XSAVES, which is compacted-format only.
@@ -447,6 +492,14 @@ static void do_extra_xstate_size_checks(
 		paranoid_xstate_size += xfeature_size(i);
 	}
 	XSTATE_WARN_ON(paranoid_xstate_size != xstate_size);
+	/*
+	 * Basically, make sure that XSTATE_RESERVE has forced
+	 * xregs_state to be large enough.  This is not fatal
+	 * because we reserve a *lot* of extra room in the init
+	 * task struct, but we should at least know we got it
+	 * wrong.
+	 */
+	XSTATE_WARN_ON(xstate_size > sizeof(struct xregs_state));
 }
 
 /*
_
--
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