On Fri, 5 Jun 2020 14:21:29 +0100
Daniel Thompson <daniel.thomp...@linaro.org> wrote:
> Currently kgdb honours the kprobe blacklist but doesn't place its own
> trap handling code on the list. Add macros to discourage attempting to
> use kgdb to debug itself.
>
> These changes do not make it impossible to provoke recursive trapping
> since they do not cover all the calls that can be made on kgdb's entry
> logic. However going much further whilst we are sharing the kprobe
> blacklist risks reducing the capabilities of kprobe and this is a bad
> trade off (especially so given kgdb's users are currently conditioned to
> avoid recursive traps).
>
> Signed-off-by: Daniel Thompson <daniel.thomp...@linaro.org>
> ---
> kernel/debug/debug_core.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> index 4a2df4509fe1..21d1d91da4bb 100644
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -184,6 +184,7 @@ int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt
> *bpt)
> return probe_kernel_write((char *)bpt->bpt_addr,
> (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
> }
> +NOKPROBE_SYMBOL(kgdb_arch_remove_breakpoint);
>
> int __weak kgdb_validate_break_address(unsigned long addr)
> {
> @@ -321,6 +322,7 @@ static void kgdb_flush_swbreak_addr(unsigned long addr)
> /* Force flush instruction cache if it was outside the mm */
> flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
> }
> +NOKPROBE_SYMBOL(kgdb_flush_swbreak_addr);
>
> /*
> * SW breakpoint management:
> @@ -411,6 +413,7 @@ int dbg_deactivate_sw_breakpoints(void)
> }
> return ret;
> }
> +NOKPROBE_SYMBOL(dbg_deactivate_sw_breakpoints);
>
> int dbg_remove_sw_break(unsigned long addr)
> {
> @@ -567,6 +570,7 @@ static int kgdb_reenter_check(struct kgdb_state *ks)
>
> return 1;
> }
> +NOKPROBE_SYMBOL(kgdb_reenter_check);
>
> static void dbg_touch_watchdogs(void)
> {
> @@ -801,6 +805,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct
> pt_regs *regs,
>
> return kgdb_info[cpu].ret_state;
> }
> +NOKPROBE_SYMBOL(kgdb_cpu_enter);
>
> /*
> * kgdb_handle_exception() - main entry point from a kernel exception
> @@ -845,6 +850,7 @@ kgdb_handle_exception(int evector, int signo, int ecode,
> struct pt_regs *regs)
> arch_kgdb_ops.enable_nmi(1);
> return ret;
> }
> +NOKPROBE_SYMBOL(kgdb_handle_exception);
>
> /*
> * GDB places a breakpoint at this function to know dynamically loaded
> objects.
> @@ -879,6 +885,7 @@ int kgdb_nmicallback(int cpu, void *regs)
> #endif
> return 1;
> }
> +NOKPROBE_SYMBOL(kgdb_nmicallback);
>
> int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
> atomic_t *send_ready)
> @@ -904,6 +911,7 @@ int kgdb_nmicallin(int cpu, int trapnr, void *regs, int
> err_code,
> #endif
> return 1;
> }
> +NOKPROBE_SYMBOL(kgdb_nmicallin);
>
> static void kgdb_console_write(struct console *co, const char *s,
> unsigned count)
> @@ -1204,7 +1212,6 @@ noinline void kgdb_breakpoint(void)
> atomic_dec(&kgdb_setting_breakpoint);
> }
> EXPORT_SYMBOL_GPL(kgdb_breakpoint);
> -NOKPROBE_SYMBOL(kgdb_breakpoint);
BTW, why did you mark this NOKPROBE in 2/4 and remove it 3/4 again?
Thank you,
--
Masami Hiramatsu <mhira...@kernel.org>
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