Messages in this thread Patch in this message | | | From | "Chang S. Bae" <> | Subject | [PATCH v11 27/29] x86/fpu/xstate: Add a sanity check for XFD state when saving XSTATE | Date | Fri, 1 Oct 2021 15:37:26 -0700 |
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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 = ¤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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