[PATCH v2] riscv: kprobes: Prevent probes in breakpoint handlers

[Rui Qi]

The ftrace selftest multiple_kprobes.tc registers kprobe events on
the first 256 text symbols from /proc/kallsyms. If handle_break() is
selected as a probe target on RISC-V, the breakpoint exception path
can trap again before it reaches the kprobe breakpoint handler. That
recursively enters do_trap_break() and can make the system
unresponsive.

Mark handle_break() and its local probe dispatch helpers as nokprobe
symbols so they are added to the kprobe blacklist, matching other
low-level breakpoint exception paths.

Signed-off-by: Rui Qi <qirui.001@xxxxxxxxxxxxx>
Reviewed-by: Nam Cao <namcao@xxxxxxxxxxxxx>
---
Changes in v2:
- Drop the blank line before NOKPROBE_SYMBOL() to match the local style.
- Add Nam's Reviewed-by tag.

 arch/riscv/kernel/traps.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 2f57fd48ec28..f8292adda099 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -269,6 +269,7 @@ static bool probe_single_step_handler(struct pt_regs *regs)
 
 	return user ? uprobe_single_step_handler(regs) : kprobe_single_step_handler(regs);
 }
+NOKPROBE_SYMBOL(probe_single_step_handler);
 
 static bool probe_breakpoint_handler(struct pt_regs *regs)
 {
@@ -276,6 +277,7 @@ static bool probe_breakpoint_handler(struct pt_regs *regs)
 
 	return user ? uprobe_breakpoint_handler(regs) : kprobe_breakpoint_handler(regs);
 }
+NOKPROBE_SYMBOL(probe_breakpoint_handler);
 
 void handle_break(struct pt_regs *regs)
 {
@@ -300,6 +302,7 @@ void handle_break(struct pt_regs *regs)
 	else
 		die(regs, "Kernel BUG");
 }
+NOKPROBE_SYMBOL(handle_break);
 
 asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
 {
-- 
2.20.1