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Message-ID: <ca7c3071f17be6fa1f29f2d62cd53a66c97ea289.camel@redhat.com>
Date: Tue, 05 Dec 2023 11:53:37 +0200
From: Maxim Levitsky <mlevitsk@...hat.com>
To: "Yang, Weijiang" <weijiang.yang@...el.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
dave.hansen@...el.com, pbonzini@...hat.com, seanjc@...gle.com,
peterz@...radead.org, chao.gao@...el.com,
rick.p.edgecombe@...el.com, john.allen@....com
Subject: Re: [PATCH v7 03/26] x86/fpu/xstate: Add CET supervisor mode state
support
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@intel.com/
> > >
> > > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > > ---
> > > 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@...hat.com>
> >
> > Best regards,
> > Maxim Levitsky
> >
> >
> >
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