[PATCH v6 17/26] x86/fpu/xstate: Disable XSTATE support if an inconsistent state is detected

[Chang S. Bae]

The kernel has a sanity check between two methods to calculate XSTATE size.
In the unlikely event that they disagree, disable the use of XSTATE.

Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Reviewed-by: Len Brown <len.brown@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
Changes from v4:
* Added as a new patch. (Thomas Gleixner)
---
 arch/x86/kernel/fpu/xstate.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 3e71aa45c5b7..08be55ac1597 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -652,11 +652,11 @@ 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 %zu bytes, cpu state %d bytes\n",	\
-		__stringify(nr_macro), sizeof(__struct), sz)) {		\
+	if ((nr == nr_macro) &&	(sz != sizeof(__struct))) {		\
+		pr_err("%s: struct is %zu bytes, cpu state %d bytes\n",	\
+		       __stringify(nr_macro), sizeof(__struct), sz);	\
 		__xstate_dump_leaves();					\
+		return -EINVAL;						\
 	}								\
 } while (0)
 
@@ -665,7 +665,7 @@ static void __xstate_dump_leaves(void)
  * that our software representation matches what the CPU
  * tells us about the state's size.
  */
-static void check_xstate_against_struct(int nr)
+static int check_xstate_against_struct(int nr)
 {
 	/*
 	 * Ask the CPU for the size of the state.
@@ -693,9 +693,12 @@ static void check_xstate_against_struct(int nr)
 	    (nr >= XFEATURE_MAX) ||
 	    (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR) ||
 	    ((nr >= XFEATURE_RSRVD_COMP_11) && (nr <= XFEATURE_LBR))) {
-		WARN_ONCE(1, "no structure for xstate: %d\n", nr);
+		pr_err("no structure for xstate: %d\n", nr);
 		XSTATE_WARN_ON(1);
+		return -EINVAL;
 	}
+
+	return 0;
 }
 
 /**
@@ -711,9 +714,9 @@ static void check_xstate_against_struct(int nr)
  * Dynamic user states are stored in this per-task buffer. They account
  * for the delta between the maximum and the minimum.
  *
- * Return: nothing.
+ * Returns 0 on success, -EINVAL on state size mismatch.
  */
-static void calculate_xstate_sizes(void)
+static int calculate_xstate_sizes(void)
 {
 	int xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
 	int xstate_size_no_dynamic, i;
@@ -722,13 +725,17 @@ static void calculate_xstate_sizes(void)
 
 	for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) {
 		bool user_dynamic;
+		int err;
 
 		if (!xfeature_enabled(i))
 			continue;
 
 		user_dynamic = (xfeatures_mask_user_dynamic & BIT_ULL(i)) ? true : false;
 
-		check_xstate_against_struct(i);
+		err = check_xstate_against_struct(i);
+		if (err)
+			return err;
+
 		/*
 		 * Supervisor state components can be managed only by
 		 * XSAVES.
@@ -770,6 +777,8 @@ static void calculate_xstate_sizes(void)
 
 	/* Record the one without dynamic states as the minimum. */
 	set_xstate_config(XSTATE_MIN_SIZE, xstate_size_no_dynamic);
+
+	return 0;
 }
 
 
@@ -856,6 +865,7 @@ static int __init init_xstate_size(void)
 	/* Recompute the context size for enabled features: */
 	unsigned int possible_xstate_size;
 	unsigned int xsave_size;
+	int err;
 
 	xsave_size = get_xsave_size();
 
@@ -872,9 +882,11 @@ static int __init init_xstate_size(void)
 
 	/*
 	 * Calculate and double-check the maximum size. Calculate and record
-	 * the minimum size.
+	 * the minimum size. Emit the error when received.
 	 */
-	calculate_xstate_sizes();
+	err = calculate_xstate_sizes();
+	if (err)
+		return err;
 
 	/* Ensure the minimum size fits in the statically-allocated buffer: */
 	if (!is_supported_xstate_size(get_xstate_config(XSTATE_MIN_SIZE)))
-- 
2.17.1