ARM: probes: avoid adding kprobes to sensitive kernel-entry/exit code

Avoid adding kprobes to any of the kernel entry/exit or startup
assembly code, or code in the identity-mapped region.  This code does
not conform to the standard C conventions, which means that the
expectations of the kprobes code is not forfilled.

Placing kprobes at some of these locations results in the kernel trying
to return to userspace addresses while retaining the CPU in kernel mode.

Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

6 files changed, 12 insertions, 25 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index fbc707626b3e..1752033b0070 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -82,11 +82,7 @@
 #endif
 	.endm
 
-#ifdef CONFIG_KPROBES
-	.section	.kprobes.text,"ax",%progbits
-#else
-	.text
-#endif
+	.section	.entry.text,"ax",%progbits
 
 /*
  * Invalid mode handlers
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index e655dcd0a933..3c4f88701f22 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -37,6 +37,7 @@ saved_pc	.req	lr
 #define TRACE(x...)
 #endif
 
+	.section .entry.text,"ax",%progbits
 	.align	5
 #if !(IS_ENABLED(CONFIG_TRACE_IRQFLAGS) || IS_ENABLED(CONFIG_CONTEXT_TRACKING))
 /*
diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index 65228bf4c6df..a56e7c856ab5 100644
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -3,6 +3,7 @@
 #include <linux/sched/debug.h>
 #include <linux/stacktrace.h>
 
+#include <asm/sections.h>
 #include <asm/stacktrace.h>
 #include <asm/traps.h>
 
@@ -63,7 +64,6 @@ EXPORT_SYMBOL(walk_stackframe);
 #ifdef CONFIG_STACKTRACE
 struct stack_trace_data {
 	struct stack_trace *trace;
-	unsigned long last_pc;
 	unsigned int no_sched_functions;
 	unsigned int skip;
 };
@@ -87,16 +87,7 @@ static int save_trace(struct stackframe *frame, void *d)
 	if (trace->nr_entries >= trace->max_entries)
 		return 1;
 
-	/*
-	 * in_exception_text() is designed to test if the PC is one of
-	 * the functions which has an exception stack above it, but
-	 * unfortunately what is in frame->pc is the return LR value,
-	 * not the saved PC value.  So, we need to track the previous
-	 * frame PC value when doing this.
-	 */
-	addr = data->last_pc;
-	data->last_pc = frame->pc;
-	if (!in_exception_text(addr))
+	if (!in_entry_text(frame->pc))
 		return 0;
 
 	regs = (struct pt_regs *)frame->sp;
@@ -114,7 +105,6 @@ static noinline void __save_stack_trace(struct task_struct *tsk,
 	struct stackframe frame;
 
 	data.trace = trace;
-	data.last_pc = ULONG_MAX;
 	data.skip = trace->skip;
 	data.no_sched_functions = nosched;
 
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 5cf04888c581..e344bdd2e5ac 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -72,7 +72,7 @@ void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long
 	printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
 #endif
 
-	if (in_exception_text(where))
+	if (in_entry_text(from))
 		dump_mem("", "Exception stack", frame + 4, frame + 4 + sizeof(struct pt_regs));
 }
 
@@ -433,7 +433,7 @@ static int call_undef_hook(struct pt_regs *regs, unsigned int instr)
 	return fn ? fn(regs, instr) : 1;
 }
 
-asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
+asmlinkage void do_undefinstr(struct pt_regs *regs)
 {
 	unsigned int instr;
 	siginfo_t info;
diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index ec4b3f94ad80..12b87591eb7c 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -96,9 +96,9 @@ SECTIONS
 	.text : {			/* Real text segment		*/
 		_stext = .;		/* Text and read-only data	*/
 			IDMAP_TEXT
-			__exception_text_start = .;
-			*(.exception.text)
-			__exception_text_end = .;
+			__entry_text_start = .;
+			*(.entry.text)
+			__entry_text_end = .;
 			IRQENTRY_TEXT
 			TEXT_TEXT
 			SCHED_TEXT
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index ee53f6518872..84a1ae3ce46e 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -105,9 +105,9 @@ SECTIONS
 	.text : {			/* Real text segment		*/
 		_stext = .;		/* Text and read-only data	*/
 			IDMAP_TEXT
-			__exception_text_start = .;
-			*(.exception.text)
-			__exception_text_end = .;
+			__entry_text_start = .;
+			*(.entry.text)
+			__entry_text_end = .;
 			IRQENTRY_TEXT
 			SOFTIRQENTRY_TEXT
 			TEXT_TEXT