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>

4 files changed, 18 insertions, 15 deletions

diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index 406746666eb7..1498d0a9c762 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -51,13 +51,16 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 	return addr;
 }
 
-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)
 {
-	struct pt_regs *regs = &fregs->regs;
+	struct pt_regs *regs = &arch_ftrace_regs(fregs)->regs;
 
 	if (test_pt_regs_flag(regs, PIF_FTRACE_FULL_REGS))
 		return regs;
@@ -84,26 +87,26 @@ static __always_inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph
 static __always_inline unsigned long
 ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs)
 {
-	return fregs->regs.psw.addr;
+	return arch_ftrace_regs(fregs)->regs.psw.addr;
 }
 
 static __always_inline void
 ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
 				    unsigned long ip)
 {
-	fregs->regs.psw.addr = ip;
+	arch_ftrace_regs(fregs)->regs.psw.addr = ip;
 }
 
 #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)
 
@@ -117,7 +120,7 @@ ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
  */
 static inline void arch_ftrace_set_direct_caller(struct ftrace_regs *fregs, unsigned long addr)
 {
-	struct pt_regs *regs = &fregs->regs;
+	struct pt_regs *regs = &arch_ftrace_regs(fregs)->regs;
 	regs->orig_gpr2 = addr;
 }
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 5529248d84fb..db9659980175 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -184,8 +184,8 @@ int main(void)
 	OFFSET(__FGRAPH_RET_FP, fgraph_ret_regs, fp);
 	DEFINE(__FGRAPH_RET_SIZE, sizeof(struct fgraph_ret_regs));
 #endif
-	OFFSET(__FTRACE_REGS_PT_REGS, ftrace_regs, regs);
-	DEFINE(__FTRACE_REGS_SIZE, sizeof(struct ftrace_regs));
+	OFFSET(__FTRACE_REGS_PT_REGS, __arch_ftrace_regs, regs);
+	DEFINE(__FTRACE_REGS_SIZE, sizeof(struct __arch_ftrace_regs));
 
 	OFFSET(__PCPU_FLAGS, pcpu, flags);
 	return 0;
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index 0b6e62d1d8b8..51439a71e392 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -318,7 +318,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 	if (bit < 0)
 		return;
 
-	kmsan_unpoison_memory(fregs, sizeof(*fregs));
+	kmsan_unpoison_memory(fregs, ftrace_regs_size());
 	regs = ftrace_get_regs(fregs);
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (!regs || unlikely(!p) || kprobe_disabled(p))
diff --git a/arch/s390/lib/test_unwind.c b/arch/s390/lib/test_unwind.c
index 8b7f981e6f34..6e42100875e7 100644
--- a/arch/s390/lib/test_unwind.c
+++ b/arch/s390/lib/test_unwind.c
@@ -270,9 +270,9 @@ static void notrace __used test_unwind_ftrace_handler(unsigned long ip,
 						      struct ftrace_ops *fops,
 						      struct ftrace_regs *fregs)
 {
-	struct unwindme *u = (struct unwindme *)fregs->regs.gprs[2];
+	struct unwindme *u = (struct unwindme *)arch_ftrace_regs(fregs)->regs.gprs[2];
 
-	u->ret = test_unwind(NULL, (u->flags & UWM_REGS) ? &fregs->regs : NULL,
+	u->ret = test_unwind(NULL, (u->flags & UWM_REGS) ? &arch_ftrace_regs(fregs)->regs : NULL,
 			     (u->flags & UWM_SP) ? u->sp : 0);
 }