Merge: arm64: debug: remove hook registration, split exception entry

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7265

JIRA: https://issues.redhat.com/browse/RHEL-65658

CONFLICTS:

    Minor context conflicts as RHEL-9 does not have the following commits:
    25b8400 ("arm64: Support Clang UBSAN trap codes for better reporting")
    d683a85 ("ubsan: Remove regs from report_ubsan_failure()")
    8ce71d2 ("arm64/traps: Handle GCS exceptions")
    1384022 ("arm64: mops: Handle MOPS exceptions from EL1")
    398edaa ("arm64/fpsimd: Do not discard modified SVE state")

This series simplifies the debug exception entry path by removing handler
registration mechanisms for the debug exception handlers, a holdover from
the arm kernel, as well as the break and stepping handlers.
This moves much of the code related to debug exceptions outside of
`mm/fault.c` where it didn't make much sense.
This allows us to split the debug exception entries: going from one common
path per EL for all debug exceptions to a unique one per exception and EL.

The result is a much simpler and fully static exception entry path, which
we tailor to the different exceptions and their constraints.
...

Original cover letter and testing procedure can be found here:

  arm64: debug: remove hook registration, split exception entry (v6)
  https://lore.kernel.org/linux-arm-kernel/20250707114109.35672-1-ada.coupriediaz@arm.com/

These are the upstream commits backported for this MR:

    ad8b226 arm64: debug: clean up single_step_handler logic
    b1e2d95 arm64: refactor aarch32_break_handler()
    9a0e3b9 arm64: Return early when break handler is found on linked-list
    3b84efc arm64: kprobes: Return DBG_HOOK_ERROR if kprobes can not handle a BRK
    2537512 arm64: kretprobes: acquire the regs via a BRK exception
    6adfdc5 arm64: debug: call software breakpoint handlers statically
    403b48a arm64: debug: call step handlers statically
    d4e0b12 arm64: debug: remove break/step handler registration infrastructure
    eaff68b arm64: entry: Add entry and exit functions for debug exceptions
    43e2ae7 arm64: debug: split hardware breakpoint exception entry
    80691d3 arm64: debug: refactor reinstall_suspended_bps()
    0ac7584 arm64: debug: split single stepping exception entry
    413f0bb arm64: debug: split hardware watchpoint exception entry
    31575e1 arm64: debug: split brk64 exception entry
    fc5e5d0 arm64: debug: split bkpt32 exception entry
    8b09788 trap: cleanup trap_init()
    a8b8cce arm64: debug: remove debug exception registration infrastructure

Special note goes for commits 9a0e3b9, 3b84efc, 2537512 and
8b09788 that were added to fix minor context conflicts. Also, commit

Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>

Approved-by: Radu Rendec <rrendec@redhat.com>
Approved-by: Alessandro Carminati <acarmina@redhat.com>
Approved-by: Aristeu Rozanski <arozansk@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>
Approved-by: Audra Mitchell <aubaker@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

arch/arc/kernel/traps.c

@@ -20,11 +20,6 @@
 #include <asm/unaligned.h>
 #include <asm/kprobes.h>
 
-void __init trap_init(void)
-{
-	return;
-}
-
 void die(const char *str, struct pt_regs *regs, unsigned long address)
 {
 	show_kernel_fault_diag(str, regs, address);

arch/arm/kernel/traps.c

@@ -781,11 +781,6 @@ void abort(void)
 	panic("Oops failed to kill thread");
 }
 
-void __init trap_init(void)
-{
-	return;
-}
-
 #ifdef CONFIG_KUSER_HELPERS
 static void __init kuser_init(void *vectors)
 {

arch/arm64/include/asm/brk-imm.h

@@ -11,6 +11,7 @@
  * 0x004: for installing kprobes
  * 0x005: for installing uprobes
  * 0x006: for kprobe software single-step
+ * 0x007: for kretprobe return
  * Allowed values for kgdb are 0x400 - 0x7ff
  * 0x100: for triggering a fault on purpose (reserved)
  * 0x400: for dynamic BRK instruction
@@ -22,6 +23,7 @@
 #define KPROBES_BRK_IMM			0x004
 #define UPROBES_BRK_IMM			0x005
 #define KPROBES_BRK_SS_IMM		0x006
+#define KRETPROBES_BRK_IMM		0x007
 #define FAULT_BRK_IMM			0x100
 #define KGDB_DYN_DBG_BRK_IMM		0x400
 #define KGDB_COMPILED_DBG_BRK_IMM	0x401

arch/arm64/include/asm/debug-monitors.h

@@ -62,30 +62,6 @@ struct task_struct;
 #define DBG_HOOK_HANDLED	0
 #define DBG_HOOK_ERROR		1
 
-struct step_hook {
-	struct list_head node;
-	int (*fn)(struct pt_regs *regs, unsigned long esr);
-};
-
-void register_user_step_hook(struct step_hook *hook);
-void unregister_user_step_hook(struct step_hook *hook);
-
-void register_kernel_step_hook(struct step_hook *hook);
-void unregister_kernel_step_hook(struct step_hook *hook);
-
-struct break_hook {
-	struct list_head node;
-	int (*fn)(struct pt_regs *regs, unsigned long esr);
-	u16 imm;
-	u16 mask; /* These bits are ignored when comparing with imm */
-};
-
-void register_user_break_hook(struct break_hook *hook);
-void unregister_user_break_hook(struct break_hook *hook);
-
-void register_kernel_break_hook(struct break_hook *hook);
-void unregister_kernel_break_hook(struct break_hook *hook);
-
 u8 debug_monitors_arch(void);
 
 enum dbg_active_el {
@@ -107,17 +83,15 @@ int kernel_active_single_step(void);
 void kernel_rewind_single_step(struct pt_regs *regs);
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-int reinstall_suspended_bps(struct pt_regs *regs);
+bool try_step_suspended_breakpoints(struct pt_regs *regs);
 #else
-static inline int reinstall_suspended_bps(struct pt_regs *regs)
+static inline bool try_step_suspended_breakpoints(struct pt_regs *regs)
 {
-	return -ENODEV;
+	return false;
 }
 #endif
 
-int aarch32_break_handler(struct pt_regs *regs);
-
-void debug_traps_init(void);
+bool try_handle_aarch32_break(struct pt_regs *regs);
 
 #endif	/* __ASSEMBLY */
 #endif	/* __ASM_DEBUG_MONITORS_H */

arch/arm64/include/asm/exception.h

@@ -57,8 +57,20 @@ void do_el0_undef(struct pt_regs *regs, unsigned long esr);
 void do_el1_undef(struct pt_regs *regs, unsigned long esr);
 void do_el0_bti(struct pt_regs *regs);
 void do_el1_bti(struct pt_regs *regs, unsigned long esr);
-void do_debug_exception(unsigned long addr_if_watchpoint, unsigned long esr,
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+void do_breakpoint(unsigned long esr, struct pt_regs *regs);
+void do_watchpoint(unsigned long addr, unsigned long esr,
 			struct pt_regs *regs);
+#else
+static inline void do_breakpoint(unsigned long esr, struct pt_regs *regs) {}
+static inline void do_watchpoint(unsigned long addr, unsigned long esr,
+			struct pt_regs *regs) {}
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+void do_el0_softstep(unsigned long esr, struct pt_regs *regs);
+void do_el1_softstep(unsigned long esr, struct pt_regs *regs);
+void do_el0_brk64(unsigned long esr, struct pt_regs *regs);
+void do_el1_brk64(unsigned long esr, struct pt_regs *regs);
+void do_bkpt32(unsigned long esr, struct pt_regs *regs);
 void do_fpsimd_acc(unsigned long esr, struct pt_regs *regs);
 void do_sve_acc(unsigned long esr, struct pt_regs *regs);
 void do_sme_acc(unsigned long esr, struct pt_regs *regs);

arch/arm64/include/asm/kgdb.h

@@ -24,6 +24,18 @@ 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);
+#ifdef CONFIG_KGDB
+int kgdb_single_step_handler(struct pt_regs *regs, unsigned long esr);
+#else
+static inline int kgdb_single_step_handler(struct pt_regs *regs,
+	unsigned long esr)
+{
+	return DBG_HOOK_ERROR;
+}
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 /*

arch/arm64/include/asm/kprobes.h

@@ -43,4 +43,12 @@ void __kretprobe_trampoline(void);
 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);
+
 #endif /* _ARM_KPROBES_H */

arch/arm64/include/asm/system_misc.h

@@ -25,10 +25,6 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
 		      int signo, int sicode, unsigned long far,
 		      unsigned long err);
 
-void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned long,
-					     struct pt_regs *),
-			   int sig, int code, const char *name);
-
 struct mm_struct;
 extern void __show_regs(struct pt_regs *);
 

arch/arm64/include/asm/traps.h

@@ -28,6 +28,12 @@ void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *s
 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);
 
 /*

arch/arm64/include/asm/uprobes.h

@@ -30,4 +30,15 @@ struct arch_uprobe {
 	bool simulate;
 };
 
+int uprobe_brk_handler(struct pt_regs *regs, unsigned long esr);
+#ifdef CONFIG_UPROBES
+int uprobe_single_step_handler(struct pt_regs *regs, unsigned long esr);
+#else
+static inline int uprobe_single_step_handler(struct pt_regs *regs,
+	unsigned long esr)
+{
+	return DBG_HOOK_ERROR;
+}
+#endif
+
 #endif