[PATCH v9 17/26] x86/fpu/xstate: Disable XSTATE support if an inconsistent state is detected

Chang S. Bae
2021-07-30T15:07:00Z

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@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from v4:
* Added as a new patch. (Thomas Gleixner)
---
arch/x86/kernel/fpu/xstate.c | 40 ++++++++++++++++++++++++------------
1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 930e72f55e75..a36e24028ca7 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -654,11 +654,11 @@ 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)

@@ -667,7 +667,7 @@ 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.
@@ -695,9 +695,12 @@ 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;
}

/**
@@ -707,13 +710,14 @@ static void check_xstate_against_struct(int nr)
* excluded. Only the size of the buffer for task->fpu is checked here.
*
* @include_dynamic_states: A knob to include dynamic states or not.
+ * @size: A pointer to record the size.
*
- * Return: The calculated xstate size.
+ * Return: 0 if successful; otherwise, error code.
*/
-static unsigned int calculate_xstate_size(bool include_dynamic_states)
+static int calculate_xstate_size(bool include_dynamic_states, unsigned int *size)
{
unsigned int xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
- int i;
+ int i, err;

for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) {
if (!xfeature_enabled(i))
@@ -722,7 +726,10 @@ static unsigned int calculate_xstate_size(bool include_dynamic_states)
if (!include_dynamic_states && (xfeatures_mask_user_dynamic & BIT_ULL(i)))
continue;

- check_xstate_against_struct(i);
+ err = check_xstate_against_struct(i);
+ if (err)
+ return err;
+
/*
* Supervisor state components can be managed only by
* XSAVES.
@@ -748,7 +755,9 @@ static unsigned int calculate_xstate_size(bool include_dynamic_states)
xstate_size += xfeature_size(i);
}

- return xstate_size;
+ if (size)
+ *size = xstate_size;
+ return 0;
}

@@ -835,6 +844,7 @@ static int __init init_xstate_size(void)
/* Recompute the context size for enabled features: */
unsigned int possible_xstate_size, xstate_size;
unsigned int xsave_size;
+ int err;

xsave_size = get_xsave_size();

@@ -848,7 +858,9 @@ static int __init init_xstate_size(void)
* 'true' to include dynamic states. Cross-check with the CPUID-
* provided size and record it.
*/
- xstate_size = calculate_xstate_size(true);
+ err = calculate_xstate_size(true, &xstate_size);
+ if (err)
+ return err;
XSTATE_WARN_ON(possible_xstate_size != xstate_size);
set_xstate_config(XSTATE_MAX_SIZE, possible_xstate_size);

@@ -857,7 +869,9 @@ static int __init init_xstate_size(void)
* 'false' to exclude dynamic states. Ensure the size fits in
* the statically-allocated buffer and record it.
*/
- xstate_size = calculate_xstate_size(false);
+ err = calculate_xstate_size(false, &xstate_size);
+ if (err)
+ return err;
if (!is_supported_xstate_size(xstate_size))
return -EINVAL;
set_xstate_config(XSTATE_MIN_SIZE, xstate_size);
--
2.17.1