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Subject[PATCH 2/5] x86/fpu/xstate: Fix supervisor xstate component offset
Date
CPUID function 0x0d, sub function (i, i > 1) returns in ebx the offset of
xstate component i. Zero is returned for a supervisor state. A supervisor
state can only be saved by XSAVES and XSAVES uses a compacted format.
There is no fixed offset for a supervisor state. This patch checks and
makes sure a supervisor state offset is not recorded or mis-used. This has
no effect in practice as we currently use no supervisor states, but it
would be good to fix.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
---
arch/x86/include/asm/fpu/types.h | 1 +
arch/x86/include/asm/fpu/xstate.h | 3 ++
arch/x86/kernel/fpu/xstate.c | 62 ++++++++++++++++++++++++---------------
3 files changed, 43 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 36b90bb..12dd648 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -122,6 +122,7 @@ enum xfeature {
#define XFEATURE_MASK_OPMASK (1 << XFEATURE_OPMASK)
#define XFEATURE_MASK_ZMM_Hi256 (1 << XFEATURE_ZMM_Hi256)
#define XFEATURE_MASK_Hi16_ZMM (1 << XFEATURE_Hi16_ZMM)
+#define XFEATURE_MASK_PT (1 << XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
#define XFEATURE_MASK_PKRU (1 << XFEATURE_PKRU)

#define XFEATURE_MASK_FPSSE (XFEATURE_MASK_FP | XFEATURE_MASK_SSE)
diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index d812cf3..92f376c 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -18,6 +18,9 @@
#define XSAVE_YMM_SIZE 256
#define XSAVE_YMM_OFFSET (XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET)

+/* Supervisor features */
+#define XFEATURE_MASK_SUPERVISOR (XFEATURE_MASK_PT)
+
/* Supported features which support lazy state saving */
#define XFEATURE_MASK_LAZY (XFEATURE_MASK_FP | \
XFEATURE_MASK_SSE | \
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index e6fcfcc6..ec7e53b 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -112,6 +112,27 @@ int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)
}
EXPORT_SYMBOL_GPL(cpu_has_xfeatures);

+static int xfeature_is_supervisor(int xfeature_nr)
+{
+ /*
+ * We currently do not support supervisor states, but if
+ * we did, we could find out like this.
+ *
+ * SDM says: If state component i is a user state component,
+ * ECX[0] return 0; if state component i is a supervisor
+ * state component, ECX[0] returns 1.
+ */
+ u32 eax, ebx, ecx, edx;
+
+ cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx);
+ return !!(ecx & 1);
+}
+
+static int xfeature_is_user(int xfeature_nr)
+{
+ return !xfeature_is_supervisor(xfeature_nr);
+}
+
/*
* When executing XSAVEOPT (or other optimized XSAVE instructions), if
* a processor implementation detects that an FPU state component is still
@@ -230,7 +251,14 @@ static void __init setup_xstate_features(void)
continue;

cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
- xstate_offsets[i] = ebx;
+
+ /*
+ * If an xfeature is supervisor state, the offset
+ * in ebx is invalid. We leave it to -1.
+ */
+ if (xfeature_is_user(i))
+ xstate_offsets[i] = ebx;
+
xstate_sizes[i] = eax;
/*
* In our xstate size checks, we assume that the
@@ -375,32 +403,20 @@ static void __init setup_init_fpu_buf(void)
copy_xregs_to_kernel_booting(&init_fpstate.xsave);
}

-static int xfeature_is_supervisor(int xfeature_nr)
-{
- /*
- * We currently do not support supervisor states, but if
- * we did, we could find out like this.
- *
- * SDM says: If state component i is a user state component,
- * ECX[0] return 0; if state component i is a supervisor
- * state component, ECX[0] returns 1.
- u32 eax, ebx, ecx, edx;
- cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx;
- return !!(ecx & 1);
- */
- return 0;
-}
-/*
-static int xfeature_is_user(int xfeature_nr)
-{
- return !xfeature_is_supervisor(xfeature_nr);
-}
-*/
-
static int xfeature_uncompacted_offset(int xfeature_nr)
{
u32 eax, ebx, ecx, edx;

+ /*
+ * Only XSAVES supports supervisor states and it uses compacted
+ * format. Checking a supervisor state's uncompacted offset is
+ * an error.
+ */
+ if (XFEATURE_MASK_SUPERVISOR & (1 << xfeature_nr)) {
+ WARN_ONCE(1, "No fixed offset for xstate %d\n", xfeature_nr);
+ return -1;
+ }
+
CHECK_XFEATURE(xfeature_nr);
cpuid_count(XSTATE_CPUID, xfeature_nr, &eax, &ebx, &ecx, &edx);
return ebx;
--
1.9.1
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