mirror of
https://github.com/torvalds/linux.git
synced 2024-11-25 13:41:51 +00:00
253751233b
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>
43 lines
1.3 KiB
C
43 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
|
|
/*
|
|
* Copyright (C) 2012 ARM Ltd.
|
|
*/
|
|
|
|
#ifndef __ASM_BRK_IMM_H
|
|
#define __ASM_BRK_IMM_H
|
|
|
|
/*
|
|
* #imm16 values used for BRK instruction generation
|
|
* 0x004: for installing kprobes
|
|
* 0x005: for installing uprobes
|
|
* 0x006: for kprobe software single-step
|
|
* 0x007: for kretprobe return
|
|
* Allowed values for kgdb are 0x400 - 0x7ff
|
|
* 0x100: for triggering a fault on purpose (reserved)
|
|
* 0x400: for dynamic BRK instruction
|
|
* 0x401: for compile time BRK instruction
|
|
* 0x800: kernel-mode BUG() and WARN() traps
|
|
* 0x9xx: tag-based KASAN trap (allowed values 0x900 - 0x9ff)
|
|
* 0x55xx: Undefined Behavior Sanitizer traps ('U' << 8)
|
|
* 0x8xxx: Control-Flow Integrity traps
|
|
*/
|
|
#define KPROBES_BRK_IMM 0x004
|
|
#define UPROBES_BRK_IMM 0x005
|
|
#define KPROBES_BRK_SS_IMM 0x006
|
|
#define KRETPROBES_BRK_IMM 0x007
|
|
#define FAULT_BRK_IMM 0x100
|
|
#define KGDB_DYN_DBG_BRK_IMM 0x400
|
|
#define KGDB_COMPILED_DBG_BRK_IMM 0x401
|
|
#define BUG_BRK_IMM 0x800
|
|
#define KASAN_BRK_IMM 0x900
|
|
#define KASAN_BRK_MASK 0x0ff
|
|
#define UBSAN_BRK_IMM 0x5500
|
|
#define UBSAN_BRK_MASK 0x00ff
|
|
|
|
#define CFI_BRK_IMM_TARGET GENMASK(4, 0)
|
|
#define CFI_BRK_IMM_TYPE GENMASK(9, 5)
|
|
#define CFI_BRK_IMM_BASE 0x8000
|
|
#define CFI_BRK_IMM_MASK (CFI_BRK_IMM_TARGET | CFI_BRK_IMM_TYPE)
|
|
|
|
#endif
|