The IA32_XFD_MSR allows to arm #NM traps for XSTATE components which are
enabled in XCR0. The register has to be restored before the tasks XSTATE is
restored. The life time rules are the same as for FPU state.

XFD is updated on return to userspace only when the FPU state of the task
is not up to date in the registers. It's updated before the XRSTORS so
that eventually enabled dynamic features are restored as well and not
brought into init state.

Also in signal handling for restoring FPU state from user space the
correctness of the XFD state has to be ensured.

Add it to CPU initialization and resume as well.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211021225527.10184-17-chang.seok.bae@intel.com

Add debug functionality to ensure that the XFD MSR is up to date for XSAVE*
and XRSTOR* operations.

 [ tglx: Improve comment. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-16-chang.seok.bae@intel.com

Add storage for XFD register state to struct fpstate. This will be used to
store the XFD MSR state. This will be used for switching the XFD MSR when
FPU content is restored.

Add a per-CPU variable to cache the current MSR value so the MSR has only
to be written when the values are different.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-15-chang.seok.bae@intel.com

XFD introduces two MSRs:

    - IA32_XFD to enable/disable a feature controlled by XFD

    - IA32_XFD_ERR to expose to the #NM trap handler which feature
      was tried to be used for the first time.

Both use the same xstate-component bitmap format, used by XCR0.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-14-chang.seok.bae@intel.com

Intel's eXtended Feature Disable (XFD) feature is an extension of the XSAVE
architecture. XFD allows the kernel to enable a feature state in XCR0 and
to receive a #NM trap when a task uses instructions accessing that state.

This is going to be used to postpone the allocation of a larger XSTATE
buffer for a task to the point where it is actually using a related
instruction after the permission to use that facility has been granted.

XFD is not used by the kernel, but only applied to userspace. This is a
matter of policy as the kernel knows how a fpstate is reallocated and the
XFD state.

The compacted XSAVE format is adjustable for dynamic features. Make XFD
depend on XSAVES.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-13-chang.seok.bae@intel.com

On exec(), extended register states saved in the buffer is cleared. With
dynamic features, each task carries variables besides the register states.
The struct fpu has permission information and struct fpstate contains
buffer size and feature masks. They are all dynamically updated with
dynamic features.

Reset the current task's entire FPU data before an exec() so that the new
task starts with default permission and fpstate.

Rename the register state reset function because the old naming confuses as
it does not reset struct fpstate.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-12-chang.seok.bae@intel.com

The default portion of the parent's FPU state is saved in a child task.
With dynamic features enabled, the non-default portion is not saved in a
child's fpstate because these register states are defined to be
caller-saved. The new task's fpstate is therefore the default buffer.

Fork inherits the permission of the parent.

Also, do not use memcpy() when TIF_NEED_FPU_LOAD is set because it is
invalid when the parent has dynamic features.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-11-chang.seok.bae@intel.com

The software reserved portion of the fxsave frame in the signal frame
is copied from structures which have been set up at boot time. With
dynamically enabled features the content of these structures is no
longer correct because the xfeatures and size can be different per task.

Calculate the software reserved portion at runtime and fill in the
xfeatures and size values from the tasks active fpstate.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-10-chang.seok.bae@intel.com

Use the current->group_leader->fpu to check for pending permissions to use
extended features and validate against the resulting user space size which
is stored in the group leaders fpu struct as well.

This prevents a task from installing a too small sized sigaltstack after
permissions to use dynamically enabled features have been granted, but
the task has not (yet) used a related instruction.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-9-chang.seok.bae@intel.com

To allow building up the infrastructure required to support dynamically
enabled FPU features, add:

 - XFEATURES_MASK_DYNAMIC

   This constant will hold xfeatures which can be dynamically enabled.

 - fpu_state_size_dynamic()

   A static branch for 64-bit and a simple 'return false' for 32-bit.

   This helper allows to add dynamic-feature-specific changes to common
   code which is shared between 32-bit and 64-bit without #ifdeffery.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-8-chang.seok.bae@intel.com

Dynamically enabled XSTATE features are by default disabled for all
processes. A process has to request permission to use such a feature.

To support this implement a architecture specific prctl() with the options:

   - ARCH_GET_XCOMP_SUPP

     Copies the supported feature bitmap into the user space provided
     u64 storage. The pointer is handed in via arg2

   - ARCH_GET_XCOMP_PERM

     Copies the process wide permitted feature bitmap into the user space
     provided u64 storage. The pointer is handed in via arg2

   - ARCH_REQ_XCOMP_PERM

     Request permission for a feature set. A feature set can be mapped to a
     facility, e.g. AMX, and can require one or more XSTATE components to
     be enabled.

     The feature argument is the number of the highest XSTATE component
     which is required for a facility to work.

     The request argument is not a user supplied bitmap because that makes
     filtering harder (think seccomp) and even impossible because to
     support 32bit tasks the argument would have to be a pointer.

The permission mechanism works this way:

   Task asks for permission for a facility and kernel checks whether that's
   supported. If supported it does:

     1) Check whether permission has already been granted

     2) Compute the size of the required kernel and user space buffer
        (sigframe) size.

     3) Validate that no task has a sigaltstack installed
        which is smaller than the resulting sigframe size

     4) Add the requested feature bit(s) to the permission bitmap of
        current->group_leader->fpu and store the sizes in the group
        leaders fpu struct as well.

If that is successful then the feature is still not enabled for any of the
tasks. The first usage of a related instruction will result in a #NM
trap. The trap handler validates the permission bit of the tasks group
leader and if permitted it installs a larger kernel buffer and transfers
the permission and size info to the new fpstate container which makes all
the FPU functions which require per task information aware of the extended
feature set.

  [ tglx: Adopted to new base code, added missing serialization,
          massaged namings, comments and changelog ]

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-7-chang.seok.bae@intel.com

The upcoming prctl() which is required to request the permission for a
dynamically enabled feature will also provide an option to retrieve the
supported features. If the CPU does not support XSAVE, the supported
features would be 0 even when the CPU supports FP and SSE.

Provide separate storage for the legacy feature set to avoid that and fill
in the bits in the legacy init function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-6-chang.seok.bae@intel.com

Dynamically enabled features can be requested by any thread of a running
process at any time. The request does neither enable the feature nor
allocate larger buffers. It just stores the permission to use the feature
by adding the features to the permission bitmap and by calculating the
required sizes for kernel and user space.

The reallocation of the kernel buffer happens when the feature is used
for the first time which is caught by an exception. The permission
bitmap is then checked and if the feature is permitted, then it becomes
fully enabled. If not, the task dies similarly to a task which uses an
undefined instruction.

The size information is precomputed to allow proper sigaltstack size checks
once the feature is permitted, but not yet in use because otherwise this
would open race windows where too small stacks could be installed causing
a later fail on signal delivery.

Initialize them to the default feature set and sizes.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-5-chang.seok.bae@intel.com

Split out the size calculation from the paranoia check so it can be used
for recalculating buffer sizes when dynamically enabled features are
supported.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
[ tglx: Adopted to changed base code ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-4-chang.seok.bae@intel.com

For historical reasons MINSIGSTKSZ is a constant which became already too
small with AVX512 support.

Add a mechanism to enforce strict checking of the sigaltstack size against
the real size of the FPU frame.

The strict check can be enabled via a config option and can also be
controlled via the kernel command line option 'strict_sas_size' independent
of the config switch.

Enabling it might break existing applications which allocate a too small
sigaltstack but 'work' because they never get a signal delivered. Though it
can be handy to filter out binaries which are not yet aware of
AT_MINSIGSTKSZ.

Also the upcoming support for dynamically enabled FPU features requires a
strict sanity check to ensure that:

   - Enabling of a dynamic feature, which changes the sigframe size fits
     into an enabled sigaltstack

   - Installing a too small sigaltstack after a dynamic feature has been
     added is not possible.

Implement the base check which is controlled by config and command line
options.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-3-chang.seok.bae@intel.com

New x86 FPU features will be very large, requiring ~10k of stack in
signal handlers.  These new features require a new approach called
"dynamic features".

The kernel currently tries to ensure that altstacks are reasonably
sized. Right now, on x86, sys_sigaltstack() requires a size of >=2k.
However, that 2k is a constant. Simply raising that 2k requirement
to >10k for the new features would break existing apps which have a
compiled-in size of 2k.

Instead of universally enforcing a larger stack, prohibit a process from
using dynamic features without properly-sized altstacks. This must be
enforced in two places:

 * A dynamic feature can not be enabled without an large-enough altstack
   for each process thread.
 * Once a dynamic feature is enabled, any request to install a too-small
   altstack will be rejected

The dynamic feature enabling code must examine each thread in a
process to ensure that the altstacks are large enough. Add a new lock
(sigaltstack_lock()) to ensure that threads can not race and change
their altstack after being examined.

Add the infrastructure in form of a config option and provide empty
stubs for architectures which do not need dynamic altstack size checks.

This implementation will be fleshed out for x86 in a future patch called

  x86/arch_prctl: Add controls for dynamic XSTATE components

  [dhansen: commit message. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211021225527.10184-2-chang.seok.bae@intel.com

No more users.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211022185313.074853631@linutronix.de

For the upcoming AMX support it's necessary to do a proper integration with
KVM. Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Convert the KVM FPU code over to this new scheme.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211022185313.019454292@linutronix.de

For the upcoming AMX support it's necessary to do a proper integration with
KVM. Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Provide:

  - An allocator which initializes the state properly

  - A replacement for the existing FPU swap mechanim

Aside of the reduced memory footprint, this also makes state switching
more efficient when TIF_FPU_NEED_LOAD is set. It does not require a
memcpy as the state is already correct in the to be swapped out fpstate.

The existing interfaces will be removed once KVM is converted over.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211022185312.954684740@linutronix.de

For the upcoming AMX support it's necessary to do a proper integration with
KVM. To avoid more nasty hackery in KVM which violate encapsulation extend
struct fpu and fpstate so the fpstate switching can be consolidated and
simplified.

Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().

With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.

Add fpu::__task_fpstate to save the regular fpstate pointer while the task
is inside vcpu_run(). Add some state fields to fpstate to indicate the
nature of the state.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211022185312.896403942@linutronix.de

Now that everything is mopped up, move all the helpers and prototypes into
the core header. They are not required by the outside.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.514095101@linutronix.de

xfeatures_mask_fpstate() is no longer valid when dynamically enabled
features come into play.

Rework restore_regs_from_fpstate() so it takes a constant mask which will
then be applied against the maximum feature set so that the restore
operation brings all features which are not in the xsave buffer xfeature
bitmap into init state.

This ensures that if the previous task used a dynamically enabled feature
that the task which restores has all unused components properly initialized.

Cleanup the last user of xfeatures_mask_fpstate() as well and remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.461348278@linutronix.de

Use the new fpu_user_cfg to retrieve the information instead of
xfeatures_mask_uabi() which will be no longer correct when dynamically
enabled features become available.

Using fpu_user_cfg is appropriate when setting XCOMP_BV in the
init_fpstate since it has space allocated for "max_features". But,
normal fpstates might only have space for default xfeatures. Since
XRSTOR* derives the format of the XSAVE buffer from XCOMP_BV, this can
lead to XRSTOR reading out of bounds.

So when copying actively used fpstate, simply read the XCOMP_BV features
bits directly out of the fpstate instead.

This correction courtesy of Dave Hansen <dave.hansen@linux.intel.com>

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.408879849@linutronix.de

Move the feature mask storage to the kernel and user config
structs. Default and maximum feature set are the same for now.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.352041752@linutronix.de

Use the new kernel and user space config storage to store and retrieve the
XSTATE buffer sizes. The default and the maximum size are the same for now,
but will change when support for dynamically enabled features is added.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.296830097@linutronix.de

The size calculations are partially unreadable gunk. Clean them up.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.241223689@linutronix.de

Clean the function up before making changes.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.184014242@linutronix.de

Provide a struct to store information about the maximum supported and the
default feature set and buffer sizes for both user and kernel space.

This allows quick retrieval of this information for the upcoming support
for dynamically enabled features.

 [ bp: Add vertical spacing between the struct members. ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211014230739.126107370@linutronix.de

For dynamically enabled features it's required to get the features which
are enabled for that context when restoring from sigframe.

The same applies for all signal frame size calculations.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/87ilxz5iew.ffs@tglx

Prepare for dynamically enabled states per task. The function needs to
retrieve the features and sizes which are valid in a fpstate
context. Retrieve them from fpstate.

Move the function declarations to the core header as they are not
required anywhere else.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.233529986@linutronix.de

With dynamically enabled features the copy function must know the features
and the size which is valid for the task. Retrieve them from fpstate.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.181495492@linutronix.de

Straight forward conversion. No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.129699950@linutronix.de

With dynamically enabled features the sigframe code must know the features
which are enabled for the task. Get them from fpstate.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.077781448@linutronix.de

With variable feature sets XSAVE[S] requires to know the feature set for
which the buffer is valid. Retrieve it from fpstate.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145323.025695590@linutronix.de

Make use of fpstate::size in various places which require the buffer size
information for sanity checks or memcpy() sizing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.973518954@linutronix.de

Add state size and feature mask information to the fpstate container. This
will be used for runtime checks with the upcoming support for dynamically
enabled features and dynamically sized buffers. That avoids conditionals
all over the place as the required information is accessible for both
default and extended buffers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.921388806@linutronix.de

In preparation for dynamically enabled FPU features move the function
out of line as the goal is to expose less and not more information.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.869001791@linutronix.de

If fork fails early then the copied task struct would carry the fpstate
pointer of the parent task.

Not a problem right now, but later when dynamically allocated buffers
are available, keeping the pointer might result in freeing the
parent's buffer. Set it to NULL which prevents that. If fork reaches
clone_thread(), the pointer will be correctly set to the new task
context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.817101108@linutronix.de

All users converted. Remove it along with the sanity checks.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.765063318@linutronix.de

Convert math emulation code to the new register storage
mechanism in preparation for dynamically sized buffers.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211013145322.711347464@linutronix.de