ftrace: Make ftrace_regs abstract from direct use

ftrace_regs was created to hold registers that store information to save
function parameters, return value and stack. Since it is a subset of
pt_regs, it should only be used by its accessor functions. But because
pt_regs can easily be taken from ftrace_regs (on most archs), it is
tempting to use it directly. But when running on other architectures, it
may fail to build or worse, build but crash the kernel!

Instead, make struct ftrace_regs an empty structure and have the
architectures define __arch_ftrace_regs and all the accessor functions
will typecast to it to get to the actual fields. This will help avoid
usage of ftrace_regs directly.

Link: https://lore.kernel.org/all/20241007171027.629bdafd@gandalf.local.home/

Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Cc: "x86@kernel.org" <x86@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Paul  Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas  Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav  Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/20241008230628.958778821@goodmis.org
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com> # s390
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 12 insertions, 9 deletions

diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 559560286e6d..e299fd47d201 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -32,39 +32,42 @@ struct dyn_arch_ftrace {
 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
 #define ftrace_init_nop ftrace_init_nop
 
-struct ftrace_regs {
+struct ftrace_regs;
+#define arch_ftrace_regs(fregs) ((struct __arch_ftrace_regs *)(fregs))
+
+struct __arch_ftrace_regs {
 	struct pt_regs regs;
 };
 
 static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *fregs)
 {
 	/* We clear regs.msr in ftrace_call */
-	return fregs->regs.msr ? &fregs->regs : NULL;
+	return arch_ftrace_regs(fregs)->regs.msr ? &arch_ftrace_regs(fregs)->regs : NULL;
 }
 
 static __always_inline void
 ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
 				    unsigned long ip)
 {
-	regs_set_return_ip(&fregs->regs, ip);
+	regs_set_return_ip(&arch_ftrace_regs(fregs)->regs, ip);
 }
 
 static __always_inline unsigned long
 ftrace_regs_get_instruction_pointer(struct ftrace_regs *fregs)
 {
-	return instruction_pointer(&fregs->regs);
+	return instruction_pointer(&arch_ftrace_regs(fregs)->regs);
 }
 
 #define ftrace_regs_get_argument(fregs, n) \
-	regs_get_kernel_argument(&(fregs)->regs, n)
+	regs_get_kernel_argument(&arch_ftrace_regs(fregs)->regs, n)
 #define ftrace_regs_get_stack_pointer(fregs) \
-	kernel_stack_pointer(&(fregs)->regs)
+	kernel_stack_pointer(&arch_ftrace_regs(fregs)->regs)
 #define ftrace_regs_return_value(fregs) \
-	regs_return_value(&(fregs)->regs)
+	regs_return_value(&arch_ftrace_regs(fregs)->regs)
 #define ftrace_regs_set_return_value(fregs, ret) \
-	regs_set_return_value(&(fregs)->regs, ret)
+	regs_set_return_value(&arch_ftrace_regs(fregs)->regs, ret)
 #define ftrace_override_function_with_return(fregs) \
-	override_function_with_return(&(fregs)->regs)
+	override_function_with_return(&arch_ftrace_regs(fregs)->regs)
 #define ftrace_regs_query_register_offset(name) \
 	regs_query_register_offset(name)