On arm64, kprobes always take an exception and so create a struct
pt_regs through the usual exception entry logic. Similarly kretprobes
taskes and exception for function entry, but for function returns it
uses a trampoline which attempts to create a struct pt_regs without
taking an exception.
This is problematic for a few reasons, including:
1) The kretprobes trampoline neither saves nor restores all of the
portions of PSTATE. Before invoking the handler it saves a number of
portions of PSTATE, and after returning from the handler it restores
NZCV before returning to the original return address provided by the
handler.
2) The kretprobe trampoline constructs the PSTATE value piecemeal from
special purpose registers as it cannot read all of PSTATE atomically
without taking an exception. This is somewhat fragile, and it's not
possible to reliably recover PSTATE information which only exists on
some physical CPUs (e.g. when SSBS support is mismatched).
Today the kretprobes trampoline does not record:
- BTYPE
- SSBS
- ALLINT
- SS
- PAN
- UAO
- DIT
- TCO
... and this will only get worse with future architecture extensions
which add more PSTATE bits.
3) The kretprobes trampoline doesn't store portions of struct pt_regs
(e.g. the PMR value when using pseudo-NMIs). Due to this, helpers
which operate on a struct pt_regs, such as interrupts_enabled(), may
not work correctly.
4) The function entry and function exit handlers run in different
contexts. The entry handler will always be run in a debug exception
context (which is currently treated as an NMI), but the return will
be treated as whatever context the instrumented function was executed
in. The differences between these contexts are liable to cause
problems (e.g. as the two can be differently interruptible or
preemptible, adversely affecting synchronization between the
handlers).
5) As the kretprobes trampoline runs in the same context as the code
being probed, it is subject to the same single-stepping context,
which may not be desirable if this is being driven by the kprobes
handlers.
Overall, this is fragile, painful to maintain, and gets in the way of
supporting other things (e.g. RELIABLE_STACKTRACE, FEAT_NMI).
This patch addresses these issues by replacing the kretprobes trampoline
with a `BRK` instruction, and using an exception boundary to acquire and
restore the regs, in the same way as the regular kprobes trampoline.
Ive tested this atop v6.8-rc3:
| KTAP version 1
| 1..1
| KTAP version 1
| # Subtest: kprobes_test
| # module: test_kprobes
| 1..7
| ok 1 test_kprobe
| ok 2 test_kprobes
| ok 3 test_kprobe_missed
| ok 4 test_kretprobe
| ok 5 test_kretprobes
| ok 6 test_stacktrace_on_kretprobe
| ok 7 test_stacktrace_on_nested_kretprobe
| # kprobes_test: pass:7 fail:0 skip:0 total:7
| # Totals: pass:7 fail:0 skip:0 total:7
| ok 1 kprobes_test
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Florent Revest <revest@chromium.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20240208145916.2004154-1-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
When building with CONFIG_UBSAN_TRAP=y on arm64, Clang encodes the UBSAN
check (handler) type in the esr. Extract this and actually report these
traps as coming from the specific UBSAN check that tripped.
Before:
Internal error: BRK handler: 00000000f20003e8 [#1] PREEMPT SMP
After:
Internal error: UBSAN: shift out of bounds: 00000000f2005514 [#1] PREEMPT SMP
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Yongqin Liu <yongqin.liu@linaro.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
Commit 36dadef23f ("kprobes: Init kprobes in early_initcall") enabled
using kprobes from early_initcall. Unfortunately at this point the
hardware debug infrastructure is not operational. The OS lock may still
be locked, and the hardware watchpoints may have unknown values when
kprobe enables debug monitors to single-step instructions.
Rather than using hardware single-step, append a BRK instruction after
the instruction to be executed out-of-line.
Fixes: 36dadef23f ("kprobes: Init kprobes in early_initcall")
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20201103134900.337243-1-jean-philippe@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>
Based on 2 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation #
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 4122 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kprobes and uprobes reserve some BRK immediates for installing their
probes. Define these along with the other reservations in brk-imm.h
and rename the ESR definitions to be consistent with the others that we
already have.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Mixing kernel and user debug hooks together is highly error-prone as it
relies on all of the hooks to figure out whether the exception came from
kernel or user, and then to act accordingly.
Make our debug hook code a little more robust by maintaining separate
hook lists for user and kernel, with separate registration functions
to force callers to be explicit about the exception levels that they
care about.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Tag-based KASAN inline instrumentation mode (which embeds checks of shadow
memory into the generated code, instead of inserting a callback) generates
a brk instruction when a tag mismatch is detected.
This commit adds a tag-based KASAN specific brk handler, that decodes the
immediate value passed to the brk instructions (to extract information
about the memory access that triggered the mismatch), reads the register
values (x0 contains the guilty address) and reports the bug.
Link: http://lkml.kernel.org/r/c91fe7684070e34dc34b419e6b69498f4dcacc2d.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Instead of reversing the header dependency between asm/bug.h and
asm/debug-monitors.h, split off the brk instruction immediate value
defines into a new header asm/brk-imm.h, and include it from both.
This solves the circular dependency issue that prevents BUG() from
being used in some header files, and keeps the definitions together.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Mark Rutland