Re: [PATCH 1/2] arm64: Blacklist non-kprobe-able symbols

[Masami Hiramatsu]

On 2015/07/06 14:03, Pratyush Anand wrote:
> Add all function symbols which are called from do_debug_exception under
> NOKPROBE_SYMBOL, as they can not kprobed.

Could you tell me how you checked that? from the code?

Thank you,

> 
> Signed-off-by: Pratyush Anand <panand@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/debug-monitors.c | 18 ++++++++++++++++++
>  arch/arm64/kernel/hw_breakpoint.c  |  8 ++++++++
>  arch/arm64/kernel/kgdb.c           |  4 ++++
>  arch/arm64/mm/fault.c              |  1 +
>  4 files changed, 31 insertions(+)
> 
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index 237a21f675fd..6d356b2cc674 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -22,6 +22,7 @@
>  #include <linux/debugfs.h>
>  #include <linux/hardirq.h>
>  #include <linux/init.h>
> +#include <linux/kprobes.h>
>  #include <linux/ptrace.h>
>  #include <linux/kprobes.h>
>  #include <linux/stat.h>
> @@ -47,6 +48,7 @@ static void mdscr_write(u32 mdscr)
>  	asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
>  	local_dbg_restore(flags);
>  }
> +NOKPROBE_SYMBOL(mdscr_write);
>  
>  static u32 mdscr_read(void)
>  {
> @@ -54,6 +56,7 @@ static u32 mdscr_read(void)
>  	asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
>  	return mdscr;
>  }
> +NOKPROBE_SYMBOL(mdscr_read);
>  
>  /*
>   * Allow root to disable self-hosted debug from userspace.
> @@ -102,6 +105,7 @@ void enable_debug_monitors(enum debug_elx el)
>  		mdscr_write(mdscr);
>  	}
>  }
> +NOKPROBE_SYMBOL(enable_debug_monitors);
>  
>  void disable_debug_monitors(enum debug_elx el)
>  {
> @@ -122,6 +126,7 @@ void disable_debug_monitors(enum debug_elx el)
>  		mdscr_write(mdscr);
>  	}
>  }
> +NOKPROBE_SYMBOL(disable_debug_monitors);
>  
>  /*
>   * OS lock clearing.
> @@ -173,6 +178,7 @@ static void set_regs_spsr_ss(struct pt_regs *regs)
>  	spsr |= DBG_SPSR_SS;
>  	regs->pstate = spsr;
>  }
> +NOKPROBE_SYMBOL(set_regs_spsr_ss);
>  
>  static void clear_regs_spsr_ss(struct pt_regs *regs)
>  {
> @@ -182,6 +188,7 @@ static void clear_regs_spsr_ss(struct pt_regs *regs)
>  	spsr &= ~DBG_SPSR_SS;
>  	regs->pstate = spsr;
>  }
> +NOKPROBE_SYMBOL(clear_regs_spsr_ss);
>  
>  /* EL1 Single Step Handler hooks */
>  static LIST_HEAD(step_hook);
> @@ -224,6 +231,7 @@ static int call_step_hook(struct pt_regs *regs, unsigned int esr)
>  
>  	return retval;
>  }
> +NOKPROBE_SYMBOL(call_step_hook);
>  
>  static int single_step_handler(unsigned long addr, unsigned int esr,
>  			       struct pt_regs *regs)
> @@ -270,6 +278,7 @@ static int single_step_handler(unsigned long addr, unsigned int esr,
>  
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(single_step_handler);
>  
>  /*
>   * Breakpoint handler is re-entrant as another breakpoint can
> @@ -306,6 +315,7 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr)
>  
>  	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
>  }
> +NOKPROBE_SYMBOL(call_break_hook);
>  
>  static int brk_handler(unsigned long addr, unsigned int esr,
>  		       struct pt_regs *regs)
> @@ -338,6 +348,7 @@ static int brk_handler(unsigned long addr, unsigned int esr,
>  
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(brk_handler);
>  
>  int aarch32_break_handler(struct pt_regs *regs)
>  {
> @@ -382,6 +393,7 @@ int aarch32_break_handler(struct pt_regs *regs)
>  	force_sig_info(SIGTRAP, &info, current);
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(aarch32_break_handler);
>  
>  static int __init debug_traps_init(void)
>  {
> @@ -403,6 +415,7 @@ void user_rewind_single_step(struct task_struct *task)
>  	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
>  		set_regs_spsr_ss(task_pt_regs(task));
>  }
> +NOKPROBE_SYMBOL(user_rewind_single_step);
>  
>  void user_fastforward_single_step(struct task_struct *task)
>  {
> @@ -418,6 +431,7 @@ void kernel_enable_single_step(struct pt_regs *regs)
>  	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
>  	enable_debug_monitors(DBG_ACTIVE_EL1);
>  }
> +NOKPROBE_SYMBOL(kernel_enable_single_step);
>  
>  void kernel_disable_single_step(void)
>  {
> @@ -425,12 +439,14 @@ void kernel_disable_single_step(void)
>  	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
>  	disable_debug_monitors(DBG_ACTIVE_EL1);
>  }
> +NOKPROBE_SYMBOL(kernel_disable_single_step);
>  
>  int kernel_active_single_step(void)
>  {
>  	WARN_ON(!irqs_disabled());
>  	return mdscr_read() & DBG_MDSCR_SS;
>  }
> +NOKPROBE_SYMBOL(kernel_active_single_step);
>  
>  /* ptrace API */
>  void user_enable_single_step(struct task_struct *task)
> @@ -438,8 +454,10 @@ void user_enable_single_step(struct task_struct *task)
>  	set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
>  	set_regs_spsr_ss(task_pt_regs(task));
>  }
> +NOKPROBE_SYMBOL(user_enable_single_step);
>  
>  void user_disable_single_step(struct task_struct *task)
>  {
>  	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
>  }
> +NOKPROBE_SYMBOL(user_disable_single_step);
> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> index 43b74a3ddaef..91b4c418abcb 100644
> --- a/arch/arm64/kernel/hw_breakpoint.c
> +++ b/arch/arm64/kernel/hw_breakpoint.c
> @@ -24,6 +24,7 @@
>  #include <linux/cpu_pm.h>
>  #include <linux/errno.h>
>  #include <linux/hw_breakpoint.h>
> +#include <linux/kprobes.h>
>  #include <linux/perf_event.h>
>  #include <linux/ptrace.h>
>  #include <linux/smp.h>
> @@ -139,6 +140,7 @@ static u64 read_wb_reg(int reg, int n)
>  
>  	return val;
>  }
> +NOKPROBE_SYMBOL(read_wb_reg);
>  
>  static void write_wb_reg(int reg, int n, u64 val)
>  {
> @@ -152,6 +154,7 @@ static void write_wb_reg(int reg, int n, u64 val)
>  	}
>  	isb();
>  }
> +NOKPROBE_SYMBOL(write_wb_reg);
>  
>  /*
>   * Convert a breakpoint privilege level to the corresponding exception
> @@ -169,6 +172,7 @@ static enum debug_elx debug_exception_level(int privilege)
>  		return -EINVAL;
>  	}
>  }
> +NOKPROBE_SYMBOL(debug_exception_level);
>  
>  enum hw_breakpoint_ops {
>  	HW_BREAKPOINT_INSTALL,
> @@ -573,6 +577,7 @@ static void toggle_bp_registers(int reg, enum debug_elx el, int enable)
>  		write_wb_reg(reg, i, ctrl);
>  	}
>  }
> +NOKPROBE_SYMBOL(toggle_bp_registers);
>  
>  /*
>   * Debug exception handlers.
> @@ -652,6 +657,7 @@ unlock:
>  
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(breakpoint_handler);
>  
>  static int watchpoint_handler(unsigned long addr, unsigned int esr,
>  			      struct pt_regs *regs)
> @@ -754,6 +760,7 @@ unlock:
>  
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(watchpoint_handler);
>  
>  /*
>   * Handle single-step exception.
> @@ -811,6 +818,7 @@ int reinstall_suspended_bps(struct pt_regs *regs)
>  
>  	return !handled_exception;
>  }
> +NOKPROBE_SYMBOL(reinstall_suspended_bps);
>  
>  /*
>   * Context-switcher for restoring suspended breakpoints.
> diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
> index 9469465a5e03..faa4d442688c 100644
> --- a/arch/arm64/kernel/kgdb.c
> +++ b/arch/arm64/kernel/kgdb.c
> @@ -22,6 +22,7 @@
>  #include <linux/irq.h>
>  #include <linux/kdebug.h>
>  #include <linux/kgdb.h>
> +#include <linux/kprobes.h>
>  #include <asm/traps.h>
>  
>  struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
> @@ -218,6 +219,7 @@ static int kgdb_brk_fn(struct pt_regs *regs, unsigned int esr)
>  	kgdb_handle_exception(1, SIGTRAP, 0, regs);
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(kgdb_brk_fn)
>  
>  static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int esr)
>  {
> @@ -226,6 +228,7 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int esr)
>  
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
>  
>  static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
>  {
> @@ -235,6 +238,7 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)
>  	kgdb_handle_exception(1, SIGTRAP, 0, regs);
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(kgdb_step_brk_fn);
>  
>  static struct break_hook kgdb_brkpt_hook = {
>  	.esr_mask	= 0xffffffff,
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 75750a91907a..0d0b02ce2074 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -561,3 +561,4 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
>  
>  	return 0;
>  }
> +NOKPROBE_SYMBOL(do_debug_exception)
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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