Re: [PATCH v7 03/26] x86/fpu/xstate: Add CET supervisor mode state support

[Maxim Levitsky]

On Fri, 2023-12-01 at 15:01 +0800, Yang, Weijiang wrote:
> On 12/1/2023 1:27 AM, Maxim Levitsky wrote:
> > On Fri, 2023-11-24 at 00:53 -0500, Yang Weijiang wrote:
> > > Add supervisor mode state support within FPU xstate management framework.
> > > Although supervisor shadow stack is not enabled/used today in kernel,KVM
> > > requires the support because when KVM advertises shadow stack feature to
> > > guest, architecturally it claims the support for both user and supervisor
> > > modes for guest OSes(Linux or non-Linux).
> > > 
> > > CET supervisor states not only includes PL{0,1,2}_SSP but also IA32_S_CET
> > > MSR, but the latter is not xsave-managed. In virtualization world, guest
> > > IA32_S_CET is saved/stored into/from VM control structure. With supervisor
> > > xstate support, guest supervisor mode shadow stack state can be properly
> > > saved/restored when 1) guest/host FPU context is swapped 2) vCPU
> > > thread is sched out/in.
> > > 
> > > The alternative is to enable it in KVM domain, but KVM maintainers NAKed
> > > the solution. The external discussion can be found at [*], it ended up
> > > with adding the support in kernel instead of KVM domain.
> > > 
> > > Note, in KVM case, guest CET supervisor state i.e., IA32_PL{0,1,2}_MSRs,
> > > are preserved after VM-Exit until host/guest fpstates are swapped, but
> > > since host supervisor shadow stack is disabled, the preserved MSRs won't
> > > hurt host.
> > > 
> > > [*]: https://lore.kernel.org/all/806e26c2-8d21-9cc9-a0b7-7787dd231729@xxxxxxxxx/
> > > 
> > > Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> > > ---
> > >   arch/x86/include/asm/fpu/types.h  | 14 ++++++++++++--
> > >   arch/x86/include/asm/fpu/xstate.h |  6 +++---
> > >   arch/x86/kernel/fpu/xstate.c      |  6 +++++-
> > >   3 files changed, 20 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> > > index eb810074f1e7..c6fd13a17205 100644
> > > --- a/arch/x86/include/asm/fpu/types.h
> > > +++ b/arch/x86/include/asm/fpu/types.h
> > > @@ -116,7 +116,7 @@ enum xfeature {
> > >   	XFEATURE_PKRU,
> > >   	XFEATURE_PASID,
> > >   	XFEATURE_CET_USER,
> > > -	XFEATURE_CET_KERNEL_UNUSED,
> > > +	XFEATURE_CET_KERNEL,
> > >   	XFEATURE_RSRVD_COMP_13,
> > >   	XFEATURE_RSRVD_COMP_14,
> > >   	XFEATURE_LBR,
> > > @@ -139,7 +139,7 @@ enum xfeature {
> > >   #define XFEATURE_MASK_PKRU		(1 << XFEATURE_PKRU)
> > >   #define XFEATURE_MASK_PASID		(1 << XFEATURE_PASID)
> > >   #define XFEATURE_MASK_CET_USER		(1 << XFEATURE_CET_USER)
> > > -#define XFEATURE_MASK_CET_KERNEL	(1 << XFEATURE_CET_KERNEL_UNUSED)
> > > +#define XFEATURE_MASK_CET_KERNEL	(1 << XFEATURE_CET_KERNEL)
> > >   #define XFEATURE_MASK_LBR		(1 << XFEATURE_LBR)
> > >   #define XFEATURE_MASK_XTILE_CFG		(1 << XFEATURE_XTILE_CFG)
> > >   #define XFEATURE_MASK_XTILE_DATA	(1 << XFEATURE_XTILE_DATA)
> > > @@ -264,6 +264,16 @@ struct cet_user_state {
> > >   	u64 user_ssp;
> > >   };
> > >   
> > > +/*
> > > + * State component 12 is Control-flow Enforcement supervisor states
> > > + */
> > > +struct cet_supervisor_state {
> > > +	/* supervisor ssp pointers  */
> > > +	u64 pl0_ssp;
> > > +	u64 pl1_ssp;
> > > +	u64 pl2_ssp;
> > > +};
> > > +
> > >   /*
> > >    * State component 15: Architectural LBR configuration state.
> > >    * The size of Arch LBR state depends on the number of LBRs (lbr_depth).
> > > diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
> > > index d4427b88ee12..3b4a038d3c57 100644
> > > --- a/arch/x86/include/asm/fpu/xstate.h
> > > +++ b/arch/x86/include/asm/fpu/xstate.h
> > > @@ -51,7 +51,8 @@
> > >   
> > >   /* All currently supported supervisor features */
> > >   #define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_PASID | \
> > > -					    XFEATURE_MASK_CET_USER)
> > > +					    XFEATURE_MASK_CET_USER | \
> > > +					    XFEATURE_MASK_CET_KERNEL)
> > >   
> > >   /*
> > >    * A supervisor state component may not always contain valuable information,
> > > @@ -78,8 +79,7 @@
> > >    * Unsupported supervisor features. When a supervisor feature in this mask is
> > >    * supported in the future, move it to the supported supervisor feature mask.
> > >    */
> > > -#define XFEATURE_MASK_SUPERVISOR_UNSUPPORTED (XFEATURE_MASK_PT | \
> > > -					      XFEATURE_MASK_CET_KERNEL)
> > > +#define XFEATURE_MASK_SUPERVISOR_UNSUPPORTED (XFEATURE_MASK_PT)
> > >   
> > >   /* All supervisor states including supported and unsupported states. */
> > >   #define XFEATURE_MASK_SUPERVISOR_ALL (XFEATURE_MASK_SUPERVISOR_SUPPORTED | \
> > > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> > > index 6e50a4251e2b..b57d909facca 100644
> > > --- a/arch/x86/kernel/fpu/xstate.c
> > > +++ b/arch/x86/kernel/fpu/xstate.c
> > > @@ -51,7 +51,7 @@ static const char *xfeature_names[] =
> > >   	"Protection Keys User registers",
> > >   	"PASID state",
> > >   	"Control-flow User registers",
> > > -	"Control-flow Kernel registers (unused)",
> > > +	"Control-flow Kernel registers",
> > >   	"unknown xstate feature",
> > >   	"unknown xstate feature",
> > >   	"unknown xstate feature",
> > > @@ -73,6 +73,7 @@ static unsigned short xsave_cpuid_features[] __initdata = {
> > >   	[XFEATURE_PT_UNIMPLEMENTED_SO_FAR]	= X86_FEATURE_INTEL_PT,
> > >   	[XFEATURE_PKRU]				= X86_FEATURE_OSPKE,
> > >   	[XFEATURE_PASID]			= X86_FEATURE_ENQCMD,
> > > +	[XFEATURE_CET_KERNEL]			= X86_FEATURE_SHSTK,
> > >   	[XFEATURE_XTILE_CFG]			= X86_FEATURE_AMX_TILE,
> > >   	[XFEATURE_XTILE_DATA]			= X86_FEATURE_AMX_TILE,
> > >   };
> > > @@ -277,6 +278,7 @@ static void __init print_xstate_features(void)
> > >   	print_xstate_feature(XFEATURE_MASK_PKRU);
> > >   	print_xstate_feature(XFEATURE_MASK_PASID);
> > >   	print_xstate_feature(XFEATURE_MASK_CET_USER);
> > > +	print_xstate_feature(XFEATURE_MASK_CET_KERNEL);
> > >   	print_xstate_feature(XFEATURE_MASK_XTILE_CFG);
> > >   	print_xstate_feature(XFEATURE_MASK_XTILE_DATA);
> > >   }
> > > @@ -346,6 +348,7 @@ static __init void os_xrstor_booting(struct xregs_state *xstate)
> > >   	 XFEATURE_MASK_BNDCSR |			\
> > >   	 XFEATURE_MASK_PASID |			\
> > >   	 XFEATURE_MASK_CET_USER |		\
> > > +	 XFEATURE_MASK_CET_KERNEL |		\
> > >   	 XFEATURE_MASK_XTILE)
> > >   
> > >   /*
> > > @@ -546,6 +549,7 @@ static bool __init check_xstate_against_struct(int nr)
> > >   	case XFEATURE_PASID:	  return XCHECK_SZ(sz, nr, struct ia32_pasid_state);
> > >   	case XFEATURE_XTILE_CFG:  return XCHECK_SZ(sz, nr, struct xtile_cfg);
> > >   	case XFEATURE_CET_USER:	  return XCHECK_SZ(sz, nr, struct cet_user_state);
> > > +	case XFEATURE_CET_KERNEL: return XCHECK_SZ(sz, nr, struct cet_supervisor_state);
> > >   	case XFEATURE_XTILE_DATA: check_xtile_data_against_struct(sz); return true;
> > >   	default:
> > >   		XSTATE_WARN_ON(1, "No structure for xstate: %d\n", nr);
> > Any reason why my reviewed-by was not added to this patch?
> 
> My apology again! I missed the Reviewed-by tag for this patch!
> 
> Appreciated for your careful review for this series!

Thank you very much!

Best regards,
	Maxim Levitsky

> 
> > Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > 
> > Best regards,
> > 	Maxim Levitsky
> > 
> > 
> >