[PATCH V2 00/41] x86/entry/64: Convert a bunch of ASM entry code into C code

From: Lai Jiangshan
Date: Sun Sep 26 2021 - 11:08:59 EST

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

Many ASM code in entry_64.S can be rewritten in C if they can be written
to be non-instrumentable and are called in the right order regarding to
whether CR3/gsbase is changed to kernel CR3/gsbase.

The patchset covert some of them to C code.

The patch 16 converts the error_entry() to C code. And patch 1-15
are preparation for it.

The patches 17-37 convert the IST entry code to C code. Many of them
are preparation for the actual conversion.

The patch 41 converts a small part of ASM code of syscall to C code which
does the checking for whether it can use sysret to return to userspace.

Some other paths can be possible to be in C code, for example: the
error exit, the syscall entry/exit. The PTI handling for them can
be in C code. But it would required the pt_regs to be copied/pushed
to the entry stack which means the C code would not be efficient.

When converting ASM to C, the most effort is to make them the same.
Almost no creative was involved. The code are kept as the same as ASM
as possible and no functional change intended unless my misunderstanding
in the ASM code was involved. The functions called by the C entry code
are checked to be ensured noinstr or __always_inline. Some of them have
more than one definitions and require some more cares from reviewers.
The comments in the ASM are also copied in the right place in the C code.

Changed from V1:
Add a fix as the patch1. Found by trying to applied Peterz's
suggestion in patch11.
The whole entry_error() is converted to C instead of partial.
The whole parnoid_entry() is converted to C instead of partial.
The asm code of "parnoid_entry() cfunc() parnoid_exit()" are
converted to C as suggested by Peterz.
Add entry64.c rather than move traps.c to arch/x86/entry/
The order of some commits is changed.
Remove two cleanups

[V1]: https://lore.kernel.org/all/20210831175025.27570-1-jiangshanlai@xxxxxxxxx/

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>

Lai Jiangshan (41):
x86/entry: Fix swapgs fence
x86/traps: Remove stack-protector from traps.c
compiler_types.h: Add __noinstr_section() for noinstr
x86/entry: Introduce __entry_text for entry code written in C
x86/entry: Move PTI_USER_* to arch/x86/include/asm/processor-flags.h
x86: Mark __native_read_cr3() & native_write_cr3() as __always_inline
x86/traps: Move the declaration of native_irq_return_iret into proto.h
x86/entry: Add arch/x86/entry/entry64.c for C entry code
x86/entry: Expose the address of .Lgs_change to entry64.c
x86/entry: Add C verion of SWITCH_TO_KERNEL_CR3 as
x86/entry: Add C user_entry_swapgs_and_fence() and
x86/traps: Move pt_regs only in fixup_bad_iret()
x86/entry: Switch the stack after error_entry() returns
x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry
objtool: Allow .entry.text function using CLD instruction
x86/entry: Implement the whole error_entry() as C code
x86/entry: Make paranoid_exit() callable
x86/entry: Call paranoid_exit() in asm_exc_nmi()
x86/entry: move PUSH_AND_CLEAR_REGS out of paranoid_entry
x86/entry: Add the C version ist_switch_to_kernel_cr3()
x86/entry: Add the C version ist_restore_cr3()
x86/entry: Add the C version get_percpu_base()
x86/entry: Add the C version ist_switch_to_kernel_gsbase()
x86/entry: Implement the C version ist_paranoid_entry()
x86/entry: Implement the C version ist_paranoid_exit()
x86/entry: Add a C macro to define the function body for IST in
x86/mce: Remove stack protector from mce/core.c
x86/debug, mce: Use C entry code
x86/idtentry.h: Move the definitions *IDTENTRY_{MCE|DEBUG}* up
x86/nmi: Use DEFINE_IDTENTRY_NMI for nmi
x86/nmi: Remove stack protector from nmi.c
x86/nmi: Use C entry code
x86/entry: Add a C macro to define the function body for IST in
.entry.text with an error code
x86/doublefault: Use C entry code
x86/sev: Add and use ist_vc_switch_off_ist()
x86/sev: Remove stack protector from sev.c
x86/sev: Use C entry code
x86/entry: Remove ASM function paranoid_entry() and paranoid_exit()
x86/entry: Remove the unused ASM macros
x86/entry: Remove save_ret from PUSH_AND_CLEAR_REGS
x86/syscall/64: Move the checking for sysret to C code

arch/x86/entry/Makefile | 5 +-
arch/x86/entry/calling.h | 142 +--------
arch/x86/entry/common.c | 73 ++++-
arch/x86/entry/entry64.c | 354 ++++++++++++++++++++++
arch/x86/entry/entry_64.S | 403 +++----------------------
arch/x86/include/asm/idtentry.h | 64 +++-
arch/x86/include/asm/processor-flags.h | 15 +
arch/x86/include/asm/proto.h | 1 +
arch/x86/include/asm/special_insns.h | 4 +-
arch/x86/include/asm/syscall.h | 2 +-
arch/x86/include/asm/traps.h | 6 +-
arch/x86/kernel/Makefile | 7 +
arch/x86/kernel/cpu/mce/Makefile | 4 +
arch/x86/kernel/nmi.c | 2 +-
arch/x86/kernel/traps.c | 33 +-
include/linux/compiler_types.h | 6 +-
tools/objtool/check.c | 2 +-
17 files changed, 580 insertions(+), 543 deletions(-)
create mode 100644 arch/x86/entry/entry64.c