Messages in this thread | | | From | Daniel Thompson <> | Subject | [RFC PATCH 0/4] kgdb: Honour the kprobe blacklist when setting breakpoints | Date | Fri, 5 Jun 2020 14:21:26 +0100 |
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kgdb has traditionally adopted a no safety rails approach to breakpoint placement. If the debugger is commanded to place a breakpoint at an address then it will do so even if that breakpoint results in kgdb becoming inoperable.
A stop-the-world debugger with memory peek/poke does intrinsically provide its operator with the means to hose their system in all manner of exciting ways (not least because stopping-the-world is already a DoS attack ;-) ) but the current no safety rail approach is not easy to defend, especially given kprobes provides us with plenty of machinery to mark parts of the kernel where breakpointing is discouraged.
This patchset introduces some safety rails by using the existing kprobes infrastructure. It does not cover all locations where breakpoints can cause trouble but it will definitely block off several avenues, including the architecture specific parts that are handled by arch_within_kprobe_blacklist().
This patch is an RFC because:
1. My workstation is still chugging through the compile testing.
2. Patch 4 needs more runtime testing.
3. The code to extract the kprobe blacklist code (patch 4 again) needs more review especially for its impact on arch specific code.
To be clear I do plan to do the detailed review of the kprobe blacklist stuff but would like to check the direction of travel first since the change is already surprisingly big and maybe there's a better way to organise things.
Daniel.
Daniel Thompson (4): kgdb: Honour the kprobe blacklist when setting breakpoints kgdb: Use the kprobe blacklist to limit single stepping kgdb: Add NOKPROBE labels on the trap handler functions kprobes: Allow the kprobes blacklist to be compiled independently
arch/Kconfig | 6 +- arch/arm/probes/kprobes/Makefile | 1 + arch/arm/probes/kprobes/blacklist.c | 37 ++++ arch/arm/probes/kprobes/core.c | 10 - arch/powerpc/kernel/Makefile | 1 + arch/powerpc/kernel/kprobes-blacklist.c | 34 ++++ arch/powerpc/kernel/kprobes.c | 8 - include/asm-generic/kprobes.h | 2 +- include/asm-generic/vmlinux.lds.h | 2 +- include/linux/kgdb.h | 1 + include/linux/kprobes.h | 29 ++- kernel/Makefile | 1 + kernel/debug/debug_core.c | 31 +++ kernel/debug/gdbstub.c | 10 +- kernel/debug/kdb/kdb_bp.c | 17 +- kernel/debug/kdb/kdb_main.c | 10 +- kernel/kprobes.c | 204 +------------------ kernel/kprobes_blacklist.c | 260 ++++++++++++++++++++++++ lib/Kconfig.kgdb | 1 + 19 files changed, 427 insertions(+), 238 deletions(-) create mode 100644 arch/arm/probes/kprobes/blacklist.c create mode 100644 arch/powerpc/kernel/kprobes-blacklist.c create mode 100644 kernel/kprobes_blacklist.c
-- 2.25.4
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