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>

arch/arm/include/asm/exception.h

@@ -10,11 +10,10 @@
 
 #include <linux/interrupt.h>
 
-#define __exception	__attribute__((section(".exception.text")))
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 #define __exception_irq_entry	__irq_entry
 #else
-#define __exception_irq_entry	__exception
+#define __exception_irq_entry
 #endif
 
 #endif /* __ASM_ARM_EXCEPTION_H */

arch/arm/include/asm/sections.h

@@ -6,4 +6,25 @@
 
 extern char _exiprom[];
 
+extern char __idmap_text_start[];
+extern char __idmap_text_end[];
+extern char __entry_text_start[];
+extern char __entry_text_end[];
+extern char __hyp_idmap_text_start[];
+extern char __hyp_idmap_text_end[];
+
+static inline bool in_entry_text(unsigned long addr)
+{
+	return memory_contains(__entry_text_start, __entry_text_end,
+			       (void *)addr, 1);
+}
+
+static inline bool in_idmap_text(unsigned long addr)
+{
+	void *a = (void *)addr;
+	return memory_contains(__idmap_text_start, __idmap_text_end, a, 1) ||
+	       memory_contains(__hyp_idmap_text_start, __hyp_idmap_text_end,
+			       a, 1);
+}
+
 #endif	/* _ASM_ARM_SECTIONS_H */

arch/arm/include/asm/traps.h

@@ -28,18 +28,6 @@ static inline int __in_irqentry_text(unsigned long ptr)
 	       ptr < (unsigned long)&__irqentry_text_end;
 }
 
-static inline int in_exception_text(unsigned long ptr)
-{
-	extern char __exception_text_start[];
-	extern char __exception_text_end[];
-	int in;
-
-	in = ptr >= (unsigned long)&__exception_text_start &&
-	     ptr < (unsigned long)&__exception_text_end;
-
-	return in ? : __in_irqentry_text(ptr);
-}
-
 extern void __init early_trap_init(void *);
 extern void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame);
 extern void ptrace_break(struct task_struct *tsk, struct pt_regs *regs);

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

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))
 /*

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;
 

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;

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

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

arch/arm/mm/fault.c

@@ -21,7 +21,6 @@
 #include <linux/highmem.h>
 #include <linux/perf_event.h>
 
-#include <asm/exception.h>
 #include <asm/pgtable.h>
 #include <asm/system_misc.h>
 #include <asm/system_info.h>
@@ -545,7 +544,7 @@ hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *)
 /*
  * Dispatch a data abort to the relevant handler.
  */
-asmlinkage void __exception
+asmlinkage void
 do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 {
 	const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
@@ -578,7 +577,7 @@ hook_ifault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *
 	ifsr_info[nr].name = name;
 }
 
-asmlinkage void __exception
+asmlinkage void
 do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
 {
 	const struct fsr_info *inf = ifsr_info + fsr_fs(ifsr);

arch/arm/probes/kprobes/core.c

@@ -32,6 +32,7 @@
 #include <linux/percpu.h>
 #include <linux/bug.h>
 #include <asm/patch.h>
+#include <asm/sections.h>
 
 #include "../decode-arm.h"
 #include "../decode-thumb.h"
@@ -64,9 +65,6 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	int is;
 	const struct decode_checker **checkers;
 
-	if (in_exception_text(addr))
-		return -EINVAL;
-
 #ifdef CONFIG_THUMB2_KERNEL
 	thumb = true;
 	addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
@@ -680,3 +678,13 @@ int __init arch_init_kprobes()
 #endif
 	return 0;
 }
+
+bool arch_within_kprobe_blacklist(unsigned long addr)
+{
+	void *a = (void *)addr;
+
+	return __in_irqentry_text(addr) ||
+	       in_entry_text(addr) ||
+	       in_idmap_text(addr) ||
+	       memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
+}