[RFC PATCH v2 0/4] Mark Kprobe debug exception paths noinstr

[Hongyan Xia]

From: Hongyan Xia <hongyan.xia@xxxxxxxxxxxxx>

Commit 879a6754d3d1 ("arm64: kprobes: Only handle faults originating
from XOL slot") and 23f851ac0078 ("arm64: kprobes: Allow reentering
kprobes while single-stepping") band-aided two corner cases in the arm64
kprobe path: Nested page faults inside Kprobe and nested Kprobe SS
handling. Although the two patches were taken, Will asked whether we
should keep patching things like this each time we find a corner case,
and whether making Kprobe noinstr is the correct answer [1].

This series attempts to do exactly that: Making the Kprobe path noinstr.
The kprobe handlers become noinstr end to end. Apart from marking
functions noinstr, we also force-inline some static inline helper
functions because certain compilers still outline them, breaking
noinstr.

Note that arm64 has no objtool so at the moment noinstr is more of a
contract that must be followed, instead of actually enforcing control
flow. Instrumentation can still happen if someone with root privileges
does something stupid, but now it is regarded as a bug rather than a
legitimate use case that the kernel needs to cover.

[1] https://lore.kernel.org/all/alpuL10h7-OK2hFb@willie-the-truck/

Changed in v2:
- Remove instrumentation_{begin/end}() markers as they do nothing
- Fold __always_inline into the patches that actually need them
- Remove the debug exception path changes unrelated to Kprobe. This
  series is only about Kprobe for now 
- Drop the kprobe_page_fault() patch for now. It's a question whether we
  even need it at all. Will send a patch for it separately.

Hongyan Xia (4):
  arm64/entry: Make debug_exception_enter/exit() noinstr
  arm64/debug: Make the Kprobe functions noinstr
  arm64/kprobes: Make the entire Kprobe noinstr
  Revert "arm64: kprobes: Allow reentering kprobes while
    single-stepping"

 arch/arm64/include/asm/esr.h       |  2 +-
 arch/arm64/include/asm/kprobes.h   | 15 ++------
 arch/arm64/include/asm/percpu.h    |  2 +-
 arch/arm64/include/asm/preempt.h   |  4 +-
 arch/arm64/include/asm/ptrace.h    |  4 +-
 arch/arm64/kernel/debug-monitors.c |  6 +--
 arch/arm64/kernel/entry-common.c   | 13 ++-----
 arch/arm64/kernel/probes/kprobes.c | 59 ++++++++++--------------------
 include/linux/kprobes.h            |  8 ++--
 9 files changed, 38 insertions(+), 75 deletions(-)

-- 
2.47.3