[PATCH v2 02/11] arm64: debug: call software break handlers statically
Ada Couprie Diaz
ada.coupriediaz at arm.com
Mon May 12 10:43:17 PDT 2025
Software breakpoints pass an immediate value in ESR ("comment") that can
be used to call a specialized handler (KGDB, KASAN...).
We do so in two different ways :
- During early boot, `early_brk64` statically checks against known
immediates and calls the corresponding handler,
- During init, handlers are dynamically registered into a list. When
called, the generic software breakpoint handler will iterate over
the list to find the appropriate handler.
The dynamic registration does not provide any benefit here as it is not
exported and all its uses are within the arm64 tree. It also depends on an
RCU list, whose safe access currently relies on the non-preemptible state
of `do_debug_exception`.
Replace the list iteration logic in `call_break_hooks` to call
the breakpoint handlers statically if they are enabled, like in
`early_brk64`.
Expose the handlers in their respective headers to be reachable from
`arch/arm64/kernel/debug-monitors.c` at link time.
Unify the naming of the software breakpoint handlers to XXX_brk_handler(),
making it clear they are related and to differentiate from the
hardware breakpoints.
Signed-off-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
---
arch/arm64/include/asm/kgdb.h | 3 +
arch/arm64/include/asm/kprobes.h | 6 ++
arch/arm64/include/asm/traps.h | 6 ++
arch/arm64/include/asm/uprobes.h | 2 +
arch/arm64/kernel/debug-monitors.c | 57 ++++++++++++++----
arch/arm64/kernel/kgdb.c | 22 ++-----
arch/arm64/kernel/probes/kprobes.c | 31 ++--------
arch/arm64/kernel/probes/kprobes_trampoline.S | 2 +-
arch/arm64/kernel/probes/uprobes.c | 9 +--
arch/arm64/kernel/traps.c | 59 ++++---------------
10 files changed, 84 insertions(+), 113 deletions(-)
diff --git a/arch/arm64/include/asm/kgdb.h b/arch/arm64/include/asm/kgdb.h
index 21fc85e9d2be..82a76b2102fb 100644
--- a/arch/arm64/include/asm/kgdb.h
+++ b/arch/arm64/include/asm/kgdb.h
@@ -24,6 +24,9 @@ static inline void arch_kgdb_breakpoint(void)
extern void kgdb_handle_bus_error(void);
extern int kgdb_fault_expected;
+int kgdb_brk_handler(struct pt_regs *regs, unsigned long esr);
+int kgdb_compiled_brk_handler(struct pt_regs *regs, unsigned long esr);
+
#endif /* !__ASSEMBLY__ */
/*
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index be7a3680dadf..b27dd6028e6a 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -38,6 +38,12 @@ struct kprobe_ctlblk {
void arch_remove_kprobe(struct kprobe *);
int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
void __kretprobe_trampoline(void);
+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);
void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
#endif /* CONFIG_KPROBES */
diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
index 82cf1f879c61..e3e8944a71c3 100644
--- a/arch/arm64/include/asm/traps.h
+++ b/arch/arm64/include/asm/traps.h
@@ -29,6 +29,12 @@ void arm64_force_sig_fault_pkey(unsigned long far, const char *str, int pkey);
void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str);
void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str);
+int bug_brk_handler(struct pt_regs *regs, unsigned long esr);
+int cfi_brk_handler(struct pt_regs *regs, unsigned long esr);
+int reserved_fault_brk_handler(struct pt_regs *regs, unsigned long esr);
+int kasan_brk_handler(struct pt_regs *regs, unsigned long esr);
+int ubsan_brk_handler(struct pt_regs *regs, unsigned long esr);
+
int early_brk64(unsigned long addr, unsigned long esr, struct pt_regs *regs);
/*
diff --git a/arch/arm64/include/asm/uprobes.h b/arch/arm64/include/asm/uprobes.h
index 014b02897f8e..3659a79a9f32 100644
--- a/arch/arm64/include/asm/uprobes.h
+++ b/arch/arm64/include/asm/uprobes.h
@@ -28,4 +28,6 @@ struct arch_uprobe {
bool simulate;
};
+int uprobe_brk_handler(struct pt_regs *regs, unsigned long esr);
+
#endif
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index 676fa0231935..4ece4a93b872 100644
--- a/arch/arm64/kernel/debug-monitors.c
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -21,8 +21,11 @@
#include <asm/cputype.h>
#include <asm/daifflags.h>
#include <asm/debug-monitors.h>
+#include <asm/kgdb.h>
+#include <asm/kprobes.h>
#include <asm/system_misc.h>
#include <asm/traps.h>
+#include <asm/uprobes.h>
/* Determine debug architecture. */
u8 debug_monitors_arch(void)
@@ -299,20 +302,50 @@ void unregister_kernel_break_hook(struct break_hook *hook)
static int call_break_hook(struct pt_regs *regs, unsigned long esr)
{
- struct break_hook *hook;
- struct list_head *list;
-
- list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
-
- /*
- * Since brk exception disables interrupt, this function is
- * entirely not preemptible, and we can use rcu list safely here.
- */
- list_for_each_entry_rcu(hook, list, node) {
- if ((esr_brk_comment(esr) & ~hook->mask) == hook->imm)
- return hook->fn(regs, esr);
+ if (user_mode(regs)) {
+#ifdef CONFIG_UPROBES
+ if (esr_brk_comment(esr) == UPROBES_BRK_IMM)
+ return uprobe_brk_handler(regs, esr);
+#endif
+ return DBG_HOOK_ERROR;
}
+ if (esr_brk_comment(esr) == BUG_BRK_IMM)
+ return bug_brk_handler(regs, esr);
+
+#ifdef CONFIG_CFI_CLANG
+ if (esr_is_cfi_brk(esr))
+ return cfi_brk_handler(regs, esr);
+#endif
+
+ if (esr_brk_comment(esr) == FAULT_BRK_IMM)
+ return reserved_fault_brk_handler(regs, esr);
+
+#ifdef CONFIG_KASAN_SW_TAGS
+ if ((esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
+ return kasan_brk_handler(regs, esr);
+#endif
+#ifdef CONFIG_UBSAN_TRAP
+ if ((esr_brk_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
+ return ubsan_brk_handler(regs, esr);
+#endif
+#ifdef CONFIG_KGDB
+ if (esr_brk_comment(esr) == KGDB_DYN_DBG_BRK_IMM)
+ return kgdb_brk_handler(regs, esr);
+ if (esr_brk_comment(esr) == KGDB_COMPILED_DBG_BRK_IMM)
+ return kgdb_compiled_brk_handler(regs, esr);
+#endif
+#ifdef CONFIG_KPROBES
+ if (esr_brk_comment(esr) == KPROBES_BRK_IMM)
+ return kprobe_brk_handler(regs, esr);
+ if (esr_brk_comment(esr) == KPROBES_BRK_SS_IMM)
+ return kprobe_ss_brk_handler(regs, esr);
+#endif
+#ifdef CONFIG_KRETPROBES
+ if (esr_brk_comment(esr) == KRETPROBES_BRK_IMM)
+ return kretprobe_brk_handler(regs, esr);
+#endif
+
return DBG_HOOK_ERROR;
}
NOKPROBE_SYMBOL(call_break_hook);
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index f3c4d3a8a20f..b5a3b9c85a65 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -234,21 +234,21 @@ int kgdb_arch_handle_exception(int exception_vector, int signo,
return err;
}
-static int kgdb_brk_fn(struct pt_regs *regs, unsigned long esr)
+int kgdb_brk_handler(struct pt_regs *regs, unsigned long esr)
{
kgdb_handle_exception(1, SIGTRAP, 0, regs);
return DBG_HOOK_HANDLED;
}
-NOKPROBE_SYMBOL(kgdb_brk_fn)
+NOKPROBE_SYMBOL(kgdb_brk_handler)
-static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned long esr)
+int kgdb_compiled_brk_handler(struct pt_regs *regs, unsigned long esr)
{
compiled_break = 1;
kgdb_handle_exception(1, SIGTRAP, 0, regs);
return DBG_HOOK_HANDLED;
}
-NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
+NOKPROBE_SYMBOL(kgdb_compiled_brk_handler);
static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned long esr)
{
@@ -260,16 +260,6 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned long esr)
}
NOKPROBE_SYMBOL(kgdb_step_brk_fn);
-static struct break_hook kgdb_brkpt_hook = {
- .fn = kgdb_brk_fn,
- .imm = KGDB_DYN_DBG_BRK_IMM,
-};
-
-static struct break_hook kgdb_compiled_brkpt_hook = {
- .fn = kgdb_compiled_brk_fn,
- .imm = KGDB_COMPILED_DBG_BRK_IMM,
-};
-
static struct step_hook kgdb_step_hook = {
.fn = kgdb_step_brk_fn
};
@@ -316,8 +306,6 @@ int kgdb_arch_init(void)
if (ret != 0)
return ret;
- register_kernel_break_hook(&kgdb_brkpt_hook);
- register_kernel_break_hook(&kgdb_compiled_brkpt_hook);
register_kernel_step_hook(&kgdb_step_hook);
return 0;
}
@@ -329,8 +317,6 @@ int kgdb_arch_init(void)
*/
void kgdb_arch_exit(void)
{
- unregister_kernel_break_hook(&kgdb_brkpt_hook);
- unregister_kernel_break_hook(&kgdb_compiled_brkpt_hook);
unregister_kernel_step_hook(&kgdb_step_hook);
unregister_die_notifier(&kgdb_notifier);
}
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index d9e462eafb95..0c5d408afd95 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -292,8 +292,8 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
return 0;
}
-static int __kprobes
-kprobe_breakpoint_handler(struct pt_regs *regs, unsigned long esr)
+int __kprobes
+kprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
{
struct kprobe *p, *cur_kprobe;
struct kprobe_ctlblk *kcb;
@@ -336,13 +336,8 @@ kprobe_breakpoint_handler(struct pt_regs *regs, unsigned long esr)
return DBG_HOOK_HANDLED;
}
-static struct break_hook kprobes_break_hook = {
- .imm = KPROBES_BRK_IMM,
- .fn = kprobe_breakpoint_handler,
-};
-
-static int __kprobes
-kprobe_breakpoint_ss_handler(struct pt_regs *regs, unsigned long esr)
+int __kprobes
+kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr)
{
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
unsigned long addr = instruction_pointer(regs);
@@ -360,13 +355,8 @@ kprobe_breakpoint_ss_handler(struct pt_regs *regs, unsigned long esr)
return DBG_HOOK_ERROR;
}
-static struct break_hook kprobes_break_ss_hook = {
- .imm = KPROBES_BRK_SS_IMM,
- .fn = kprobe_breakpoint_ss_handler,
-};
-
-static int __kprobes
-kretprobe_breakpoint_handler(struct pt_regs *regs, unsigned long esr)
+int __kprobes
+kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
{
if (regs->pc != (unsigned long)__kretprobe_trampoline)
return DBG_HOOK_ERROR;
@@ -375,11 +365,6 @@ kretprobe_breakpoint_handler(struct pt_regs *regs, unsigned long esr)
return DBG_HOOK_HANDLED;
}
-static struct break_hook kretprobes_break_hook = {
- .imm = KRETPROBES_BRK_IMM,
- .fn = kretprobe_breakpoint_handler,
-};
-
/*
* Provide a blacklist of symbols identifying ranges which cannot be kprobed.
* This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
@@ -422,9 +407,5 @@ int __kprobes arch_trampoline_kprobe(struct kprobe *p)
int __init arch_init_kprobes(void)
{
- register_kernel_break_hook(&kprobes_break_hook);
- register_kernel_break_hook(&kprobes_break_ss_hook);
- register_kernel_break_hook(&kretprobes_break_hook);
-
return 0;
}
diff --git a/arch/arm64/kernel/probes/kprobes_trampoline.S b/arch/arm64/kernel/probes/kprobes_trampoline.S
index a362f3dbb3d1..b60739d3983f 100644
--- a/arch/arm64/kernel/probes/kprobes_trampoline.S
+++ b/arch/arm64/kernel/probes/kprobes_trampoline.S
@@ -12,7 +12,7 @@
SYM_CODE_START(__kretprobe_trampoline)
/*
* Trigger a breakpoint exception. The PC will be adjusted by
- * kretprobe_breakpoint_handler(), and no subsequent instructions will
+ * kretprobe_brk_handler(), and no subsequent instructions will
* be executed from the trampoline.
*/
brk #KRETPROBES_BRK_IMM
diff --git a/arch/arm64/kernel/probes/uprobes.c b/arch/arm64/kernel/probes/uprobes.c
index cb3d05af36e3..ad68b4a5974d 100644
--- a/arch/arm64/kernel/probes/uprobes.c
+++ b/arch/arm64/kernel/probes/uprobes.c
@@ -173,7 +173,7 @@ int arch_uprobe_exception_notify(struct notifier_block *self,
return NOTIFY_DONE;
}
-static int uprobe_breakpoint_handler(struct pt_regs *regs,
+int uprobe_brk_handler(struct pt_regs *regs,
unsigned long esr)
{
if (uprobe_pre_sstep_notifier(regs))
@@ -194,12 +194,6 @@ static int uprobe_single_step_handler(struct pt_regs *regs,
return DBG_HOOK_ERROR;
}
-/* uprobe breakpoint handler hook */
-static struct break_hook uprobes_break_hook = {
- .imm = UPROBES_BRK_IMM,
- .fn = uprobe_breakpoint_handler,
-};
-
/* uprobe single step handler hook */
static struct step_hook uprobes_step_hook = {
.fn = uprobe_single_step_handler,
@@ -207,7 +201,6 @@ static struct step_hook uprobes_step_hook = {
static int __init arch_init_uprobes(void)
{
- register_user_break_hook(&uprobes_break_hook);
register_user_step_hook(&uprobes_step_hook);
return 0;
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 529cff825531..50d7a6a75f45 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -987,7 +987,7 @@ void do_serror(struct pt_regs *regs, unsigned long esr)
int is_valid_bugaddr(unsigned long addr)
{
/*
- * bug_handler() only called for BRK #BUG_BRK_IMM.
+ * bug_brk_handler() only called for BRK #BUG_BRK_IMM.
* So the answer is trivial -- any spurious instances with no
* bug table entry will be rejected by report_bug() and passed
* back to the debug-monitors code and handled as a fatal
@@ -997,7 +997,7 @@ int is_valid_bugaddr(unsigned long addr)
}
#endif
-static int bug_handler(struct pt_regs *regs, unsigned long esr)
+int bug_brk_handler(struct pt_regs *regs, unsigned long esr)
{
switch (report_bug(regs->pc, regs)) {
case BUG_TRAP_TYPE_BUG:
@@ -1017,13 +1017,8 @@ static int bug_handler(struct pt_regs *regs, unsigned long esr)
return DBG_HOOK_HANDLED;
}
-static struct break_hook bug_break_hook = {
- .fn = bug_handler,
- .imm = BUG_BRK_IMM,
-};
-
#ifdef CONFIG_CFI_CLANG
-static int cfi_handler(struct pt_regs *regs, unsigned long esr)
+int cfi_brk_handler(struct pt_regs *regs, unsigned long esr)
{
unsigned long target;
u32 type;
@@ -1046,15 +1041,9 @@ static int cfi_handler(struct pt_regs *regs, unsigned long esr)
arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
return DBG_HOOK_HANDLED;
}
-
-static struct break_hook cfi_break_hook = {
- .fn = cfi_handler,
- .imm = CFI_BRK_IMM_BASE,
- .mask = CFI_BRK_IMM_MASK,
-};
#endif /* CONFIG_CFI_CLANG */
-static int reserved_fault_handler(struct pt_regs *regs, unsigned long esr)
+int reserved_fault_brk_handler(struct pt_regs *regs, unsigned long esr)
{
pr_err("%s generated an invalid instruction at %pS!\n",
"Kernel text patching",
@@ -1064,11 +1053,6 @@ static int reserved_fault_handler(struct pt_regs *regs, unsigned long esr)
return DBG_HOOK_ERROR;
}
-static struct break_hook fault_break_hook = {
- .fn = reserved_fault_handler,
- .imm = FAULT_BRK_IMM,
-};
-
#ifdef CONFIG_KASAN_SW_TAGS
#define KASAN_ESR_RECOVER 0x20
@@ -1076,7 +1060,7 @@ static struct break_hook fault_break_hook = {
#define KASAN_ESR_SIZE_MASK 0x0f
#define KASAN_ESR_SIZE(esr) (1 << ((esr) & KASAN_ESR_SIZE_MASK))
-static int kasan_handler(struct pt_regs *regs, unsigned long esr)
+int kasan_brk_handler(struct pt_regs *regs, unsigned long esr)
{
bool recover = esr & KASAN_ESR_RECOVER;
bool write = esr & KASAN_ESR_WRITE;
@@ -1107,26 +1091,14 @@ static int kasan_handler(struct pt_regs *regs, unsigned long esr)
arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
return DBG_HOOK_HANDLED;
}
-
-static struct break_hook kasan_break_hook = {
- .fn = kasan_handler,
- .imm = KASAN_BRK_IMM,
- .mask = KASAN_BRK_MASK,
-};
#endif
#ifdef CONFIG_UBSAN_TRAP
-static int ubsan_handler(struct pt_regs *regs, unsigned long esr)
+int ubsan_brk_handler(struct pt_regs *regs, unsigned long esr)
{
die(report_ubsan_failure(regs, esr & UBSAN_BRK_MASK), regs, esr);
return DBG_HOOK_HANDLED;
}
-
-static struct break_hook ubsan_break_hook = {
- .fn = ubsan_handler,
- .imm = UBSAN_BRK_IMM,
- .mask = UBSAN_BRK_MASK,
-};
#endif
/*
@@ -1138,31 +1110,20 @@ int __init early_brk64(unsigned long addr, unsigned long esr,
{
#ifdef CONFIG_CFI_CLANG
if (esr_is_cfi_brk(esr))
- return cfi_handler(regs, esr) != DBG_HOOK_HANDLED;
+ return cfi_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
#endif
#ifdef CONFIG_KASAN_SW_TAGS
if ((esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
- return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
+ return kasan_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
#endif
#ifdef CONFIG_UBSAN_TRAP
if ((esr_brk_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
- return ubsan_handler(regs, esr) != DBG_HOOK_HANDLED;
+ return ubsan_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
#endif
- return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
+ return bug_brk_handler(regs, esr) != DBG_HOOK_HANDLED;
}
void __init trap_init(void)
{
- register_kernel_break_hook(&bug_break_hook);
-#ifdef CONFIG_CFI_CLANG
- register_kernel_break_hook(&cfi_break_hook);
-#endif
- register_kernel_break_hook(&fault_break_hook);
-#ifdef CONFIG_KASAN_SW_TAGS
- register_kernel_break_hook(&kasan_break_hook);
-#endif
-#ifdef CONFIG_UBSAN_TRAP
- register_kernel_break_hook(&ubsan_break_hook);
-#endif
debug_traps_init();
}
--
2.43.0
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