linux-stable.git/arch/x86/kernel/process_64.c, branch v6.2

Merge tag 'x86_core_for_v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-12-14T23:03:00+00:00

Pull x86 core updates from Borislav Petkov:

 - Add the call depth tracking mitigation for Retbleed which has been
   long in the making. It is a lighterweight software-only fix for
   Skylake-based cores where enabling IBRS is a big hammer and causes a
   significant performance impact.

   What it basically does is, it aligns all kernel functions to 16 bytes
   boundary and adds a 16-byte padding before the function, objtool
   collects all functions' locations and when the mitigation gets
   applied, it patches a call accounting thunk which is used to track
   the call depth of the stack at any time.

   When that call depth reaches a magical, microarchitecture-specific
   value for the Return Stack Buffer, the code stuffs that RSB and
   avoids its underflow which could otherwise lead to the Intel variant
   of Retbleed.

   This software-only solution brings a lot of the lost performance
   back, as benchmarks suggest:

       https://lore.kernel.org/all/20220915111039.092790446@infradead.org/

   That page above also contains a lot more detailed explanation of the
   whole mechanism

 - Implement a new control flow integrity scheme called FineIBT which is
   based on the software kCFI implementation and uses hardware IBT
   support where present to annotate and track indirect branches using a
   hash to validate them

 - Other misc fixes and cleanups

* tag 'x86_core_for_v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (80 commits)
  x86/paravirt: Use common macro for creating simple asm paravirt functions
  x86/paravirt: Remove clobber bitmask from .parainstructions
  x86/debug: Include percpu.h in debugreg.h to get DECLARE_PER_CPU() et al
  x86/cpufeatures: Move X86_FEATURE_CALL_DEPTH from bit 18 to bit 19 of word 11, to leave space for WIP X86_FEATURE_SGX_EDECCSSA bit
  x86/Kconfig: Enable kernel IBT by default
  x86,pm: Force out-of-line memcpy()
  objtool: Fix weak hole vs prefix symbol
  objtool: Optimize elf_dirty_reloc_sym()
  x86/cfi: Add boot time hash randomization
  x86/cfi: Boot time selection of CFI scheme
  x86/ibt: Implement FineIBT
  objtool: Add --cfi to generate the .cfi_sites section
  x86: Add prefix symbols for function padding
  objtool: Add option to generate prefix symbols
  objtool: Avoid O(bloody terrible) behaviour -- an ode to libelf
  objtool: Slice up elf_create_section_symbol()
  kallsyms: Revert "Take callthunks into account"
  x86: Unconfuse CONFIG_ and X86_FEATURE_ namespaces
  x86/retpoline: Fix crash printing warning
  x86/paravirt: Fix a !PARAVIRT build warning
  ...

x86/cpu: Switch to cpu_feature_enabled() for X86_FEATURE_XENPV

2022-11-22T15:18:19+00:00

Convert the remaining cases of static_cpu_has(X86_FEATURE_XENPV) and
boot_cpu_has(X86_FEATURE_XENPV) to use cpu_feature_enabled(), allowing
more efficient code in case the kernel is configured without
CONFIG_XEN_PV.

Signed-off-by: Juergen Gross 
Signed-off-by: Borislav Petkov 
Acked-by: Dave Hansen 
Link: https://lore.kernel.org/r/20221104072701.20283-6-jgross@suse.com

x86/percpu: Move irq_stack variables next to current_task

2022-10-17T14:41:05+00:00

Further extend struct pcpu_hot with the hard and soft irq stack
pointers.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220915111145.599170752@infradead.org

x86/percpu: Move current_top_of_stack next to current_task

2022-10-17T14:41:05+00:00

Extend the struct pcpu_hot cacheline with current_top_of_stack;
another very frequently used value.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220915111145.493038635@infradead.org

x86: Put hot per CPU variables into a struct

2022-10-17T14:41:03+00:00

The layout of per-cpu variables is at the mercy of the compiler. This
can lead to random performance fluctuations from build to build.

Create a structure to hold some of the hottest per-cpu variables,
starting with current_task.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220915111145.179707194@infradead.org

x86: kmsan: skip shadow checks in __switch_to()

2022-10-03T21:03:24+00:00

When instrumenting functions, KMSAN obtains the per-task state (mostly
pointers to metadata for function arguments and return values) once per
function at its beginning, using the `current` pointer.

Every time the instrumented function calls another function, this state
(`struct kmsan_context_state`) is updated with shadow/origin data of the
passed and returned values.

When `current` changes in the low-level arch code, instrumented code can
not notice that, and will still refer to the old state, possibly
corrupting it or using stale data.  This may result in false positive
reports.

To deal with that, we need to apply __no_kmsan_checks to the functions
performing context switching - this will result in skipping all KMSAN
shadow checks and marking newly created values as initialized, preventing
all false positive reports in those functions.  False negatives are still
possible, but we expect them to be rare and impersistent.

Link: https://lkml.kernel.org/r/20220915150417.722975-34-glider@google.com
Suggested-by: Marco Elver 
Signed-off-by: Alexander Potapenko 
Cc: Alexander Viro 
Cc: Alexei Starovoitov 
Cc: Andrey Konovalov 
Cc: Andrey Konovalov 
Cc: Andy Lutomirski 
Cc: Arnd Bergmann 
Cc: Borislav Petkov 
Cc: Christoph Hellwig 
Cc: Christoph Lameter 
Cc: David Rientjes 
Cc: Dmitry Vyukov 
Cc: Eric Biggers 
Cc: Eric Biggers 
Cc: Eric Dumazet 
Cc: Greg Kroah-Hartman 
Cc: Herbert Xu 
Cc: Ilya Leoshkevich 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Joonsoo Kim 
Cc: Kees Cook 
Cc: Mark Rutland 
Cc: Matthew Wilcox 
Cc: Michael S. Tsirkin 
Cc: Pekka Enberg 
Cc: Peter Zijlstra 
Cc: Petr Mladek 
Cc: Stephen Rothwell 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Vasily Gorbik 
Cc: Vegard Nossum 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

x86/prctl: Remove pointless task argument

2022-05-13T10:56:28+00:00

The functions invoked via do_arch_prctl_common() can only operate on
the current task and none of these function uses the task argument.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Link: https://lore.kernel.org/r/87lev7vtxj.ffs@tglx

x86: Remove toolchain check for X32 ABI capability

2022-03-15T09:32:48+00:00

Commit 0bf6276392e9 ("x32: Warn and disable rather than error if
binutils too old") added a small test in arch/x86/Makefile because
binutils 2.22 or newer is needed to properly support elf32-x86-64. This
check is no longer necessary, as the minimum supported version of
binutils is 2.23, which is enforced at configuration time with
scripts/min-tool-version.sh.

Remove this check and replace all uses of CONFIG_X86_X32 with
CONFIG_X86_X32_ABI, as two symbols are no longer necessary.

[nathan: Rebase, fix up a few places where CONFIG_X86_X32 was still
         used, and simplify commit message to satisfy -tip requirements]

Signed-off-by: Masahiro Yamada 
Signed-off-by: Nathan Chancellor 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220314194842.3452-2-nathan@kernel.org

x86/fpu: Move context switch and exit to user inlines into sched.h

2021-10-20T13:27:27+00:00

internal.h is a kitchen sink which needs to get out of the way to prepare
for the upcoming changes.

Move the context switch and exit to user inlines into a separate header,
which is all that code needs.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20211015011539.349132461@linutronix.de

x86/fpu: Remove pointless argument from switch_fpu_finish()

2021-10-20T13:27:25+00:00

Unused since the FPU switching rework.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Borislav Petkov 
Link: https://lkml.kernel.org/r/20211015011538.433135710@linutronix.de