arm64: refactor aarch32_break_handler()

`aarch32_break_handler()` is called in `do_el0_undef()` when we
are trying to handle an exception whose Exception Syndrome is unknown.
It checks if the instruction hit might be a 32-bit arm break (be it
A32 or T2), and sends a SIGTRAP to userspace if it is so that it can
be handled.

However, this is badly represented in the naming of the function, and
is not consistent with the other functions called with the same logic
in `do_el0_undef()`.

Rename it `try_handle_aarch32_break()` and change the return value to
a boolean to align with the logic of the other tentative handlers in
`do_el0_undef()`, the previous error code being ignored anyway.

Signed-off-by: Ada Couprie Diaz <[email protected]>
Tested-by: Luis Claudio R. Goncalves <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Reviewed-by: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Ada Couprie Diaz

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

@@ -116,7 +116,7 @@ static inline int reinstall_suspended_bps(struct pt_regs *regs)
 }
 #endif
 
-int aarch32_break_handler(struct pt_regs *regs);
+bool try_handle_aarch32_break(struct pt_regs *regs);
 
 void debug_traps_init(void);
 

arch/arm64/kernel/debug-monitors.c

@@ -334,15 +334,15 @@ static int brk_handler(unsigned long unused, unsigned long esr,
 }
 NOKPROBE_SYMBOL(brk_handler);
 
-int aarch32_break_handler(struct pt_regs *regs)
+bool try_handle_aarch32_break(struct pt_regs *regs)
 {
 	u32 arm_instr;
 	u16 thumb_instr;
 	bool bp = false;
 	void __user *pc = (void __user *)instruction_pointer(regs);
 
 	if (!compat_user_mode(regs))
-		return -EFAULT;
+		return false;
 
 	if (compat_thumb_mode(regs)) {
 		/* get 16-bit Thumb instruction */
@@ -366,12 +366,12 @@ int aarch32_break_handler(struct pt_regs *regs)
 	}
 
 	if (!bp)
-		return -EFAULT;
+		return false;
 
 	send_user_sigtrap(TRAP_BRKPT);
-	return 0;
+	return true;
 }
-NOKPROBE_SYMBOL(aarch32_break_handler);
+NOKPROBE_SYMBOL(try_handle_aarch32_break);
 
 void __init debug_traps_init(void)
 {

arch/arm64/kernel/traps.c

@@ -454,7 +454,7 @@ void do_el0_undef(struct pt_regs *regs, unsigned long esr)
 	u32 insn;
 
 	/* check for AArch32 breakpoint instructions */
-	if (!aarch32_break_handler(regs))
+	if (try_handle_aarch32_break(regs))
 		return;
 
 	if (user_insn_read(regs, &insn))