patches/kernel/0015-x86-fpu-Allow-caller-to-constrain-xfeatures-when-cop.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Sean Christopherson <seanjc@google.com>
   3 Date: Wed, 27 Sep 2023 17:19:52 -0700
   4 Subject: [PATCH] x86/fpu: Allow caller to constrain xfeatures when copying to
   5  uabi buffer
   6
   7 Plumb an xfeatures mask into __copy_xstate_to_uabi_buf() so that KVM can
   8 constrain which xfeatures are saved into the userspace buffer without
   9 having to modify the user_xfeatures field in KVM's guest_fpu state.
  10
  11 KVM's ABI for KVM_GET_XSAVE{2} is that features that are not exposed to
  12 guest must not show up in the effective xstate_bv field of the buffer.
  13 Saving only the guest-supported xfeatures allows userspace to load the
  14 saved state on a different host with a fewer xfeatures, so long as the
  15 target host supports the xfeatures that are exposed to the guest.
  16
  17 KVM currently sets user_xfeatures directly to restrict KVM_GET_XSAVE{2} to
  18 the set of guest-supported xfeatures, but doing so broke KVM's historical
  19 ABI for KVM_SET_XSAVE, which allows userspace to load any xfeatures that
  20 are supported by the *host*.
  21
  22 Cc: stable@vger.kernel.org
  23 Signed-off-by: Sean Christopherson <seanjc@google.com>
  24 Message-Id: <20230928001956.924301-2-seanjc@google.com>
  25 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  26 (cherry picked from commit 18164f66e6c59fda15c198b371fa008431efdb22)
  27 Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  28 ---
  29  arch/x86/include/asm/fpu/api.h |  3 ++-
  30  arch/x86/kernel/fpu/core.c     |  5 +++--
  31  arch/x86/kernel/fpu/xstate.c   |  7 +++++--
  32  arch/x86/kernel/fpu/xstate.h   |  3 ++-
  33  arch/x86/kvm/x86.c             | 21 +++++++++------------
  34  5 files changed, 21 insertions(+), 18 deletions(-)
  35
  36 diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
  37 index b475d9a582b8..e829fa4c6788 100644
  38 --- a/arch/x86/include/asm/fpu/api.h
  39 +++ b/arch/x86/include/asm/fpu/api.h
  40 @@ -148,7 +148,8 @@ static inline void fpu_update_guest_xfd(struct fpu_guest *guest_fpu, u64 xfd) {
  41  static inline void fpu_sync_guest_vmexit_xfd_state(void) { }
  42  #endif
  43
  44 -extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf, unsigned int size, u32 pkru);
  45 +extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
  46 +                                          unsigned int size, u64 xfeatures, u32 pkru);
  47  extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
  48
  49  static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
  50 diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
  51 index 98e507cc7d34..b582325b9c37 100644
  52 --- a/arch/x86/kernel/fpu/core.c
  53 +++ b/arch/x86/kernel/fpu/core.c
  54 @@ -369,14 +369,15 @@ int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
  55  EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
  56
  57  void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
  58 -                                   unsigned int size, u32 pkru)
  59 +                                   unsigned int size, u64 xfeatures, u32 pkru)
  60  {
  61         struct fpstate *kstate = gfpu->fpstate;
  62         union fpregs_state *ustate = buf;
  63         struct membuf mb = { .p = buf, .left = size };
  64
  65         if (cpu_feature_enabled(X86_FEATURE_XSAVE)) {
  66 -               __copy_xstate_to_uabi_buf(mb, kstate, pkru, XSTATE_COPY_XSAVE);
  67 +               __copy_xstate_to_uabi_buf(mb, kstate, xfeatures, pkru,
  68 +                                         XSTATE_COPY_XSAVE);
  69         } else {
  70                 memcpy(&ustate->fxsave, &kstate->regs.fxsave,
  71                        sizeof(ustate->fxsave));
  72 diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
  73 index 1afbc4866b10..463ec0cd0dab 100644
  74 --- a/arch/x86/kernel/fpu/xstate.c
  75 +++ b/arch/x86/kernel/fpu/xstate.c
  76 @@ -1053,6 +1053,7 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
  77   * __copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
  78   * @to:                membuf descriptor
  79   * @fpstate:   The fpstate buffer from which to copy
  80 + * @xfeatures: The mask of xfeatures to save (XSAVE mode only)
  81   * @pkru_val:  The PKRU value to store in the PKRU component
  82   * @copy_mode: The requested copy mode
  83   *
  84 @@ -1063,7 +1064,8 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
  85   * It supports partial copy but @to.pos always starts from zero.
  86   */
  87  void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
  88 -                              u32 pkru_val, enum xstate_copy_mode copy_mode)
  89 +                              u64 xfeatures, u32 pkru_val,
  90 +                              enum xstate_copy_mode copy_mode)
  91  {
  92         const unsigned int off_mxcsr = offsetof(struct fxregs_state, mxcsr);
  93         struct xregs_state *xinit = &init_fpstate.regs.xsave;
  94 @@ -1087,7 +1089,7 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
  95                 break;
  96
  97         case XSTATE_COPY_XSAVE:
  98 -               header.xfeatures &= fpstate->user_xfeatures;
  99 +               header.xfeatures &= fpstate->user_xfeatures & xfeatures;
 100                 break;
 101         }
 102
 103 @@ -1189,6 +1191,7 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
 104                              enum xstate_copy_mode copy_mode)
 105  {
 106         __copy_xstate_to_uabi_buf(to, tsk->thread.fpu.fpstate,
 107 +                                 tsk->thread.fpu.fpstate->user_xfeatures,
 108                                   tsk->thread.pkru, copy_mode);
 109  }
 110
 111 diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
 112 index a4ecb04d8d64..3518fb26d06b 100644
 113 --- a/arch/x86/kernel/fpu/xstate.h
 114 +++ b/arch/x86/kernel/fpu/xstate.h
 115 @@ -43,7 +43,8 @@ enum xstate_copy_mode {
 116
 117  struct membuf;
 118  extern void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
 119 -                                     u32 pkru_val, enum xstate_copy_mode copy_mode);
 120 +                                     u64 xfeatures, u32 pkru_val,
 121 +                                     enum xstate_copy_mode copy_mode);
 122  extern void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
 123                                     enum xstate_copy_mode mode);
 124  extern int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u32 *pkru);
 125 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
 126 index 6690a3722007..394d3a8b4682 100644
 127 --- a/arch/x86/kvm/x86.c
 128 +++ b/arch/x86/kvm/x86.c
 129 @@ -5385,26 +5385,23 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 130         return 0;
 131  }
 132
 133 -static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
 134 -                                        struct kvm_xsave *guest_xsave)
 135 +
 136 +static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
 137 +                                         u8 *state, unsigned int size)
 138  {
 139         if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 140                 return;
 141
 142 -       fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
 143 -                                      guest_xsave->region,
 144 -                                      sizeof(guest_xsave->region),
 145 +       fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu, state, size,
 146 +                                      vcpu->arch.guest_fpu.fpstate->user_xfeatures,
 147                                        vcpu->arch.pkru);
 148  }
 149
 150 -static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
 151 -                                         u8 *state, unsigned int size)
 152 +static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
 153 +                                        struct kvm_xsave *guest_xsave)
 154  {
 155 -       if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
 156 -               return;
 157 -
 158 -       fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
 159 -                                      state, size, vcpu->arch.pkru);
 160 +       return kvm_vcpu_ioctl_x86_get_xsave2(vcpu, (void *)guest_xsave->region,
 161 +                                            sizeof(guest_xsave->region));
 162  }
 163
 164  static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,