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Date: Fri, 1 Oct 2021 15:37:26 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: bp@...e.de, luto@...nel.org, tglx@...utronix.de, mingo@...nel.org,
x86@...nel.org
Cc: len.brown@...el.com, lenb@...nel.org, dave.hansen@...el.com,
thiago.macieira@...el.com, jing2.liu@...el.com,
ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
chang.seok.bae@...el.com
Subject: [PATCH v11 27/29] x86/fpu/xstate: Add a sanity check for XFD state when saving XSTATE
Add a DEBUG sanity check that XFD state matches with XINUSE state.
Instead of reading MSR IA32_XFD directly, read a per-cpu value that is
recorded at every MSR write.
Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
Changes from v9:
* Re-introduce xfd_write() to record every XFD write.
* Use cpu_feature_enabled() instead of boot_cpu_has(). (Borislav Petkov)
Changes from v5:
* Added as a new patch. (Dave Hansen)
---
arch/x86/include/asm/fpu/internal.h | 22 +++++++++++++++++++++-
arch/x86/kernel/fpu/core.c | 13 +++++++++++++
arch/x86/kernel/fpu/xstate.c | 12 +++++-------
arch/x86/kernel/traps.c | 9 ++++-----
4 files changed, 43 insertions(+), 13 deletions(-)
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 5f013fa0b205..1129abc6ae06 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -556,6 +556,26 @@ static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu)
* Misc helper functions:
*/
+#ifdef CONFIG_X86_DEBUG_FPU
+DECLARE_PER_CPU(u64, xfd_shadow);
+static inline u64 xfd_debug_shadow(void)
+{
+ return this_cpu_read(xfd_shadow);
+}
+
+static inline void xfd_write(u64 value)
+{
+ wrmsrl_safe(MSR_IA32_XFD, value);
+ this_cpu_write(xfd_shadow, value);
+}
+#else
+#define xfd_debug_shadow() 0
+static inline void xfd_write(u64 value)
+{
+ wrmsrl_safe(MSR_IA32_XFD, value);
+}
+#endif
+
/**
* xfd_switch - Switches the MSR IA32_XFD context if needed.
* @prev: The previous task's struct fpu pointer
@@ -572,7 +592,7 @@ static inline void xfd_switch(struct fpu *prev, struct fpu *next)
next_xfd_mask = next->state_mask & xfeatures_mask_user_dynamic;
if (unlikely(prev_xfd_mask != next_xfd_mask))
- wrmsrl_safe(MSR_IA32_XFD, xfeatures_mask_user_dynamic ^ next_xfd_mask);
+ xfd_write(xfeatures_mask_user_dynamic ^ next_xfd_mask);
}
/*
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index fdac0f430af3..be6c210c00d4 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -82,6 +82,10 @@ bool irq_fpu_usable(void)
}
EXPORT_SYMBOL(irq_fpu_usable);
+#ifdef CONFIG_X86_DEBUG_FPU
+DEFINE_PER_CPU(u64, xfd_shadow);
+#endif
+
/*
* Save the FPU register state in fpu->state. The register state is
* preserved.
@@ -99,6 +103,15 @@ EXPORT_SYMBOL(irq_fpu_usable);
void save_fpregs_to_fpstate(struct fpu *fpu)
{
if (likely(use_xsave())) {
+ /*
+ * If XFD is armed for an xfeature, XSAVE* will not save
+ * its state. Verify XFD is clear for all features that
+ * are in use before XSAVE*.
+ */
+ if (IS_ENABLED(CONFIG_X86_DEBUG_FPU) && cpu_feature_enabled(X86_FEATURE_XFD) &&
+ cpu_feature_enabled(X86_FEATURE_XGETBV1))
+ WARN_ON_FPU(xgetbv(1) & xfd_debug_shadow());
+
os_xsave(&fpu->state->xsave, fpu->state_mask);
/*
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 43539893dd82..81566a18643b 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -269,7 +269,7 @@ void fpu__init_cpu_xstate(void)
}
if (boot_cpu_has(X86_FEATURE_XFD))
- wrmsrl(MSR_IA32_XFD, xfeatures_mask_user_dynamic);
+ xfd_write(xfeatures_mask_user_dynamic);
}
static bool xfeature_enabled(enum xfeature xfeature)
@@ -1095,9 +1095,8 @@ void fpu__resume_cpu(void)
}
if (cpu_feature_enabled(X86_FEATURE_XFD))
- wrmsrl_safe(MSR_IA32_XFD, (current->thread.fpu.state_mask &
- xfeatures_mask_user_dynamic) ^
- xfeatures_mask_user_dynamic);
+ xfd_write((current->thread.fpu.state_mask & xfeatures_mask_user_dynamic) ^
+ xfeatures_mask_user_dynamic);
}
/**
@@ -1325,9 +1324,8 @@ void reset_state_perm(struct task_struct *tsk)
if (cpu_feature_enabled(X86_FEATURE_XSAVES))
fpstate_init_xstate(&fpu->state->xsave, fpu->state_mask);
- wrmsrl_safe(MSR_IA32_XFD,
- (fpu->state_mask & xfeatures_mask_user_dynamic) ^
- xfeatures_mask_user_dynamic);
+ xfd_write((fpu->state_mask & xfeatures_mask_user_dynamic) ^
+ xfeatures_mask_user_dynamic);
}
/**
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bbf30e73d156..cc19b570b322 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1129,7 +1129,7 @@ static __always_inline bool handle_xfd_event(struct fpu *fpu, struct pt_regs *re
* unblock the task.
*/
rdmsrl_safe(MSR_IA32_XFD, &value);
- wrmsrl_safe(MSR_IA32_XFD, value & ~xfd_err);
+ xfd_write(value & ~xfd_err);
} else {
struct fpu *fpu = ¤t->thread.fpu;
int err = -1;
@@ -1148,10 +1148,9 @@ static __always_inline bool handle_xfd_event(struct fpu *fpu, struct pt_regs *re
if (!WARN_ON(in_interrupt())) {
err = realloc_xstate_buffer(fpu, xfd_event);
if (!err)
- wrmsrl_safe(MSR_IA32_XFD,
- (fpu->state_mask &
- xfeatures_mask_user_dynamic) ^
- xfeatures_mask_user_dynamic);
+ xfd_write((fpu->state_mask &
+ xfeatures_mask_user_dynamic) ^
+ xfeatures_mask_user_dynamic);
}
if (err)
--
2.17.1
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