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471f0aa7fa
When an extended state component is not present in fpstate, but in init
state, the function copies from init_fpstate via copy_feature().
But, dynamic states are not present in init_fpstate because of all-zeros
init states. Then retrieving them from init_fpstate will explode like this:
BUG: kernel NULL pointer dereference, address: 0000000000000000
...
RIP: 0010:memcpy_erms+0x6/0x10
? __copy_xstate_to_uabi_buf+0x381/0x870
fpu_copy_guest_fpstate_to_uabi+0x28/0x80
kvm_arch_vcpu_ioctl+0x14c/0x1460 [kvm]
? __this_cpu_preempt_check+0x13/0x20
? vmx_vcpu_put+0x2e/0x260 [kvm_intel]
kvm_vcpu_ioctl+0xea/0x6b0 [kvm]
? kvm_vcpu_ioctl+0xea/0x6b0 [kvm]
? __fget_light+0xd4/0x130
__x64_sys_ioctl+0xe3/0x910
? debug_smp_processor_id+0x17/0x20
? fpregs_assert_state_consistent+0x27/0x50
do_syscall_64+0x3f/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Adjust the 'mask' to zero out the userspace buffer for the features that
are not available both from fpstate and from init_fpstate.
The dynamic features depend on the compacted XSAVE format. Ensure it is
enabled before reading XCOMP_BV in init_fpstate.
Fixes: 2308ee57d9 ("x86/fpu/amx: Enable the AMX feature in 64-bit mode")
Reported-by: Yuan Yao <yuan.yao@intel.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/lkml/BYAPR11MB3717EDEF2351C958F2C86EED95259@BYAPR11MB3717.namprd11.prod.outlook.com/
Link: https://lkml.kernel.org/r/20221021185844.13472-1-chang.seok.bae@intel.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.