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

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/1350

JIRA: https://issues.redhat.com/browse/RHEL-69599

CONFLICTS:
    minor conflict, more context than functionality, as RHEL-10 does not have
    commit d683a85 ("ubsan: Remove regs from report_ubsan_failure()")

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()
    dc1fd37 arm64: Introduce esr_is_ubsan_brk()
    6adfdc5 arm64: debug: call software breakpoint handlers statically
    403b48a arm64: debug: call step handlers statically
    d4e0b12 arm64: debug: remove break/step handler registration infrastructure
    398edaa arm64/fpsimd: Do not discard modified SVE state
    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
    a8b8cce arm64: debug: remove debug exception registration infrastructure

Special note goes for commit dc1fd37 that was added to fix a minor context
conflict and commit 398edaa that is both required context and a fix.

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

Approved-by: Gabriele Monaco <gmonaco@redhat.com>
Approved-by: Rafael Aquini <raquini@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Scott Weaver <scweaver@redhat.com>

Author: swvrrh

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 {
@@ -108,17 +84,15 @@ void kernel_rewind_single_step(struct pt_regs *regs);
 void kernel_fastforward_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/esr.h

@@ -440,6 +440,11 @@ static inline bool esr_is_cfi_brk(unsigned long esr)
 	       (esr_brk_comment(esr) & ~CFI_BRK_IMM_MASK) == CFI_BRK_IMM_BASE;
 }
 
+static inline bool esr_is_ubsan_brk(unsigned long esr)
+{
+	return (esr_brk_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM;
+}
+
 static inline bool esr_fsc_is_translation_fault(unsigned long esr)
 {
 	esr = esr & ESR_ELx_FSC;

arch/arm64/include/asm/exception.h

@@ -59,8 +59,20 @@ void do_el0_bti(struct pt_regs *regs);
 void do_el1_bti(struct pt_regs *regs, unsigned long esr);
 void do_el0_gcs(struct pt_regs *regs, unsigned long esr);
 void do_el1_gcs(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/fpsimd.h

@@ -6,6 +6,7 @@
 #define __ASM_FP_H
 
 #include <asm/errno.h>
+#include <asm/percpu.h>
 #include <asm/ptrace.h>
 #include <asm/processor.h>
 #include <asm/sigcontext.h>
@@ -94,6 +95,8 @@ struct cpu_fp_state {
 	enum fp_type to_save;
 };
 
+DECLARE_PER_CPU(struct cpu_fp_state, fpsimd_last_state);
+
 extern void fpsimd_bind_state_to_cpu(struct cpu_fp_state *fp_state);
 
 extern void fpsimd_flush_task_state(struct task_struct *target);

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

@@ -41,4 +41,12 @@ 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

@@ -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);
 
 /*

arch/arm64/include/asm/uprobes.h

@@ -28,4 +28,15 @@ 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