[PATCH v5 18/28] x86/fpu/xstate: Disable xstate support if an inconsistent state is detected

Chang S. Bae
2021-05-23T19:39:18Z

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 | 33 ++++++++++++++++++++++-----------
1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 1cf5888210aa..544e35a9d777 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -730,11 +730,11 @@ 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)

@@ -743,7 +743,7 @@ 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.
@@ -771,9 +771,12 @@ 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;
}

/**
@@ -786,9 +789,9 @@ static void check_xstate_against_struct(int nr)
*
* Dynamic supervisor XSAVE features allocate their own buffers and are not covered by these checks.
*
- * Return: nothing.
+ * Returns 0 on success, -EINVAL on state size mismatch.
*/
-static void calculate_xstate_sizes(void)
+static int calculate_xstate_sizes(void)
{
int paranoid_min_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
int paranoid_max_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
@@ -796,13 +799,17 @@ 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, which is compacted-format only.
@@ -837,6 +844,7 @@ static void calculate_xstate_sizes(void)
}
XSTATE_WARN_ON(paranoid_max_size != get_xstate_config(XSTATE_MAX_SIZE));
set_xstate_config(XSTATE_MIN_SIZE, paranoid_min_size);
+ return 0;
}

@@ -923,6 +931,7 @@ 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();

@@ -939,9 +948,11 @@ 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-alocated buffer: */
if (!is_supported_xstate_size(get_xstate_config(XSTATE_MIN_SIZE)))
--
2.17.1