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    Subject[PATCH v11 27/29] x86/fpu/xstate: Add a sanity check for XFD state when saving XSTATE
    Date
    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@linux.intel.com>
    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 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 = &current->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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