[RFC PATCH v2 2/4] arm64/debug: Make the Kprobe functions noinstr

[Hongyan Xia]

From: Hongyan Xia <hongyan.xia at transsion.com>

The Kprobe debug exception path must be run with extra care. NOKPROBE
isn't sufficient, as other instrumentation like ftrace still opens a can
of worms that is very complex to deal with.

Mark the three main Kprobe entry points noinstr, as well as the debug
exception paths that lead to and exit from these entry points. Note that
noinstr attribute is stronger and can safely replace NOKPROBE and
__kprobe modifiers.

Also mark esr_brk_comment() __always_inline, as clang does not
reliably inline plain static inline functions into noinline (noinstr)
callers such as call_el1_break_hook().

Signed-off-by: Hongyan Xia <hongyan.xia at transsion.com>
---
 arch/arm64/include/asm/esr.h       | 2 +-
 arch/arm64/include/asm/kprobes.h   | 9 +++------
 arch/arm64/kernel/debug-monitors.c | 6 ++----
 arch/arm64/kernel/probes/kprobes.c | 6 +++---
 4 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index f816f5d77f1a..a75bfdb7e5fe 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -437,7 +437,7 @@
 #ifndef __ASSEMBLER__
 #include <asm/types.h>
 
-static inline unsigned long esr_brk_comment(unsigned long esr)
+static __always_inline unsigned long esr_brk_comment(unsigned long esr)
 {
 	return esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
 }
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index 35ce2c94040e..a694f7d34f45 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -48,11 +48,8 @@ void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
 
 #endif /* CONFIG_KPROBES */
 
-int __kprobes kprobe_brk_handler(struct pt_regs *regs,
-				 unsigned long esr);
-int __kprobes kprobe_ss_brk_handler(struct pt_regs *regs,
-				 unsigned long esr);
-int __kprobes kretprobe_brk_handler(struct pt_regs *regs,
-				 unsigned long esr);
+int noinstr kprobe_brk_handler(struct pt_regs *regs, unsigned long esr);
+int noinstr kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr);
+int noinstr kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr);
 
 #endif /* _ARM_KPROBES_H */
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 29307642f4c9..5cf4fb8ddf83 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -207,7 +207,7 @@ void do_el1_softstep(unsigned long esr, struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(do_el1_softstep);
 
-static int call_el1_break_hook(struct pt_regs *regs, unsigned long esr)
+static int noinstr call_el1_break_hook(struct pt_regs *regs, unsigned long esr)
 {
 	if (esr_brk_comment(esr) == BUG_BRK_IMM)
 		return bug_brk_handler(regs, esr);
@@ -245,7 +245,6 @@ static int call_el1_break_hook(struct pt_regs *regs, unsigned long esr)
 
 	return DBG_HOOK_ERROR;
 }
-NOKPROBE_SYMBOL(call_el1_break_hook);
 
 /*
  * We have already unmasked interrupts and enabled preemption
@@ -261,14 +260,13 @@ void do_el0_brk64(unsigned long esr, struct pt_regs *regs)
 	send_user_sigtrap(TRAP_BRKPT);
 }
 
-void do_el1_brk64(unsigned long esr, struct pt_regs *regs)
+void noinstr do_el1_brk64(unsigned long esr, struct pt_regs *regs)
 {
 	if (call_el1_break_hook(regs, esr) == DBG_HOOK_HANDLED)
 		return;
 
 	die("Oops - BRK", regs, esr);
 }
-NOKPROBE_SYMBOL(do_el1_brk64);
 
 #ifdef CONFIG_COMPAT
 void do_bkpt32(unsigned long esr, struct pt_regs *regs)
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 4e0efad5caf2..0e66abf9958e 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -350,7 +350,7 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 	return 0;
 }
 
-int __kprobes
+int noinstr
 kprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
 {
 	struct kprobe *p, *cur_kprobe;
@@ -394,7 +394,7 @@ kprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
 	return DBG_HOOK_HANDLED;
 }
 
-int __kprobes
+int noinstr
 kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
@@ -413,7 +413,7 @@ kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr)
 	return DBG_HOOK_ERROR;
 }
 
-int __kprobes
+int noinstr
 kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
 {
 	if (regs->pc != (unsigned long)__kretprobe_trampoline)
-- 
2.47.3