linux.git/arch/x86/kernel/cpu/common.c, branch v5.14

Merge tag 'x86-fpu-2021-07-07' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-07-07T18:12:01+00:00

Pull x86 fpu updates from Thomas Gleixner:
 "Fixes and improvements for FPU handling on x86:

   - Prevent sigaltstack out of bounds writes.

     The kernel unconditionally writes the FPU state to the alternate
     stack without checking whether the stack is large enough to
     accomodate it.

     Check the alternate stack size before doing so and in case it's too
     small force a SIGSEGV instead of silently corrupting user space
     data.

   - MINSIGSTKZ and SIGSTKSZ are constants in signal.h and have never
     been updated despite the fact that the FPU state which is stored on
     the signal stack has grown over time which causes trouble in the
     field when AVX512 is available on a CPU. The kernel does not expose
     the minimum requirements for the alternate stack size depending on
     the available and enabled CPU features.

     ARM already added an aux vector AT_MINSIGSTKSZ for the same reason.
     Add it to x86 as well.

   - A major cleanup of the x86 FPU code. The recent discoveries of
     XSTATE related issues unearthed quite some inconsistencies,
     duplicated code and other issues.

     The fine granular overhaul addresses this, makes the code more
     robust and maintainable, which allows to integrate upcoming XSTATE
     related features in sane ways"

* tag 'x86-fpu-2021-07-07' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (74 commits)
  x86/fpu/xstate: Clear xstate header in copy_xstate_to_uabi_buf() again
  x86/fpu/signal: Let xrstor handle the features to init
  x86/fpu/signal: Handle #PF in the direct restore path
  x86/fpu: Return proper error codes from user access functions
  x86/fpu/signal: Split out the direct restore code
  x86/fpu/signal: Sanitize copy_user_to_fpregs_zeroing()
  x86/fpu/signal: Sanitize the xstate check on sigframe
  x86/fpu/signal: Remove the legacy alignment check
  x86/fpu/signal: Move initial checks into fpu__restore_sig()
  x86/fpu: Mark init_fpstate __ro_after_init
  x86/pkru: Remove xstate fiddling from write_pkru()
  x86/fpu: Don't store PKRU in xstate in fpu_reset_fpstate()
  x86/fpu: Remove PKRU handling from switch_fpu_finish()
  x86/fpu: Mask PKRU from kernel XRSTOR[S] operations
  x86/fpu: Hook up PKRU into ptrace()
  x86/fpu: Add PKRU storage outside of task XSAVE buffer
  x86/fpu: Dont restore PKRU in fpregs_restore_userspace()
  x86/fpu: Rename xfeatures_mask_user() to xfeatures_mask_uabi()
  x86/fpu: Move FXSAVE_LEAK quirk info __copy_kernel_to_fpregs()
  x86/fpu: Rename __fpregs_load_activate() to fpregs_restore_userregs()
  ...

Merge tag 'x86-asm-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-28T19:57:11+00:00

Pull x86 asm updates from Ingo Molnar:

 - Micro-optimize and standardize the do_syscall_64() calling convention

 - Make syscall entry flags clearing more conservative

 - Clean up syscall table handling

 - Clean up & standardize assembly macros, in preparation of FRED

 - Misc cleanups and fixes

* tag 'x86-asm-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/asm: Make  valid on cross-builds as well
  x86/regs: Syscall_get_nr() returns -1 for a non-system call
  x86/entry: Split PUSH_AND_CLEAR_REGS into two submacros
  x86/syscall: Maximize MSR_SYSCALL_MASK
  x86/syscall: Unconditionally prototype {ia32,x32}_sys_call_table[]
  x86/entry: Reverse arguments to do_syscall_64()
  x86/entry: Unify definitions from  and 
  x86/asm: Use _ASM_BYTES() in 
  x86/asm: Add _ASM_BYTES() macro for a .byte ... opcode sequence
  x86/asm: Have the __ASM_FORM macros handle commas in arguments

x86/cpu: Write the default PKRU value when enabling PKE

2021-06-23T17:14:54+00:00

In preparation of making the PKRU management more independent from XSTATES,
write the default PKRU value into the hardware right after enabling PKRU in
CR4. This ensures that switch_to() and copy_thread() have the correct
setting for init task and the per CPU idle threads right away.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20210623121455.622983906@linutronix.de

x86/cpu: Sanitize X86_FEATURE_OSPKE

2021-06-23T16:59:44+00:00

X86_FEATURE_OSPKE is enabled first on the boot CPU and the feature flag is
set. Secondary CPUs have to enable CR4.PKE as well and set their per CPU
feature flag. That's ineffective because all call sites have checks for
boot_cpu_data.

Make it smarter and force the feature flag when PKU is enabled on the boot
cpu which allows then to use cpu_feature_enabled(X86_FEATURE_OSPKE) all
over the place. That either compiles the code out when PKEY support is
disabled in Kconfig or uses a static_cpu_has() for the feature check which
makes a significant difference in hotpaths, e.g. context switch.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Reviewed-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20210623121455.305113644@linutronix.de

x86/fpu: Get rid of fpu__get_supported_xfeatures_mask()

2021-06-23T15:49:46+00:00

This function is really not doing what the comment advertises:

 "Find supported xfeatures based on cpu features and command-line input.
  This must be called after fpu__init_parse_early_param() is called and
  xfeatures_mask is enumerated."

fpu__init_parse_early_param() does not exist anymore and the function just
returns a constant.

Remove it and fix the caller and get rid of further references to
fpu__init_parse_early_param().

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Reviewed-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20210623121451.816404717@linutronix.de

x86/pkeys: Revert a5eff7259790 ("x86/pkeys: Add PKRU value to init_fpstate")

2021-06-23T15:49:45+00:00

This cannot work and it's unclear how that ever made a difference.

init_fpstate.xsave.header.xfeatures is always 0 so get_xsave_addr() will
always return a NULL pointer, which will prevent storing the default PKRU
value in init_fpstate.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Reviewed-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20210623121451.451391598@linutronix.de

x86/signal: Introduce helpers to get the maximum signal frame size

2021-05-19T09:46:27+00:00

Signal frames do not have a fixed format and can vary in size when a number
of things change: supported XSAVE features, 32 vs. 64-bit apps, etc.

Add support for a runtime method for userspace to dynamically discover
how large a signal stack needs to be.

Introduce a new variable, max_frame_size, and helper functions for the
calculation to be used in a new user interface. Set max_frame_size to a
system-wide worst-case value, instead of storing multiple app-specific
values.

Signed-off-by: Chang S. Bae 
Signed-off-by: Borislav Petkov 
Reviewed-by: Len Brown 
Acked-by: Thomas Gleixner 
Acked-by: H.J. Lu 
Link: https://lkml.kernel.org/r/20210518200320.17239-3-chang.seok.bae@intel.com

x86/cpu: Init AP exception handling from cpu_init_secondary()

2021-05-18T12:49:21+00:00

SEV-ES guests require properly setup task register with which the TSS
descriptor in the GDT can be located so that the IST-type #VC exception
handler which they need to function properly, can be executed.

This setup needs to happen before attempting to load microcode in
ucode_cpu_init() on secondary CPUs which can cause such #VC exceptions.

Simplify the machinery by running that exception setup from a new function
cpu_init_secondary() and explicitly call cpu_init_exception_handling() for
the boot CPU before cpu_init(). The latter prepares for fixing and
simplifying the exception/IST setup on the boot CPU.

There should be no functional changes resulting from this patch.

[ tglx: Reworked it so cpu_init_exception_handling() stays seperate ]

Signed-off-by: Borislav Petkov 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Lai Jiangshan 
Acked-by: Peter Zijlstra (Intel)                                                                                                                                                                                                                         
Link: https://lore.kernel.org/r/87k0o6gtvu.ffs@nanos.tec.linutronix.de

x86/syscall: Maximize MSR_SYSCALL_MASK

2021-05-12T08:49:15+00:00

It is better to clear as many flags as possible when we do a system
call entry, as opposed to the other way around. The fewer flags we
keep, the lesser the possible interference between the kernel and user
space.

The flags changed are:

 - CF, PF, AF, ZF, SF, OF: these are arithmetic flags which affect
   branches, possibly speculatively. They should be cleared for the same
   reasons we now clear all GPRs on entry.

 - RF: suppresses a code breakpoint on the subsequent instruction. It is
   probably impossible to enter the kernel with RF set, but if it is
   somehow not, it would break a kernel debugger setting a breakpoint on
   the entry point. Either way, user space should not be able to control
   kernel behavior here.

 - ID: this flag has no direct effect (it is a scratch bit only.)
   However, there is no reason to retain the user space value in the
   kernel, and the standard should be to clear unless needed, not the
   other way around.

Signed-off-by: H. Peter Anvin (Intel) 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20210510185316.3307264-5-hpa@zytor.com

x86/cpu: Remove write_tsc() and write_rdtscp_aux() wrappers

2021-05-05T19:50:14+00:00

Drop write_tsc() and write_rdtscp_aux(); the former has no users, and the
latter has only a single user and is slightly misleading since the only
in-kernel consumer of MSR_TSC_AUX is RDPID, not RDTSCP.

No functional change intended.

Signed-off-by: Sean Christopherson 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210504225632.1532621-3-seanjc@google.com