x86/entry: Unbreak __irqentry_text_start/end magic

The entry rework moved interrupt entry code from the irqentry to the
noinstr section which made the irqentry section empty.

This breaks boundary checks which rely on the __irqentry_text_start/end
markers to find out whether a function in a stack trace is
interrupt/exception entry code. This affects the function graph tracer and
filter_irq_stacks().

As the IDT entry points are all sequentialy emitted this is rather simple
to unbreak by injecting __irqentry_text_start/end as global labels.

To make this work correctly:

  - Remove the IRQENTRY_TEXT section from the x86 linker script
  - Define __irqentry so it breaks the build if it's used
  - Adjust the entry mirroring in PTI
  - Remove the redundant kprobes and unwinder bound checks
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/entry/entry_32.S

@@ -743,10 +743,19 @@ SYM_CODE_END(asm_\cfunc)
 
 /*
  * Include the defines which emit the idt entries which are shared
- * shared between 32 and 64 bit.
+ * shared between 32 and 64 bit and emit the __irqentry_text_* markers
+ * so the stacktrace boundary checks work.
  */
+	.align 16
+	.globl __irqentry_text_start
+__irqentry_text_start:
+
 #include <asm/idtentry.h>
 
+	.align 16
+	.globl __irqentry_text_end
+__irqentry_text_end:
+
 /*
  * %eax: prev task
  * %edx: next task

arch/x86/entry/entry_64.S

@@ -478,10 +478,19 @@ SYM_CODE_END(\asmsym)
 
 /*
  * Include the defines which emit the idt entries which are shared
- * shared between 32 and 64 bit.
+ * shared between 32 and 64 bit and emit the __irqentry_text_* markers
+ * so the stacktrace boundary checks work.
  */
+	.align 16
+	.globl __irqentry_text_start
+__irqentry_text_start:
+
 #include <asm/idtentry.h>
 
+	.align 16
+	.globl __irqentry_text_end
+__irqentry_text_end:
+
 SYM_CODE_START_LOCAL(common_interrupt_return)
 SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
 #ifdef CONFIG_DEBUG_ENTRY

arch/x86/include/asm/irq.h

@@ -11,6 +11,13 @@
 #include <asm/apicdef.h>
 #include <asm/irq_vectors.h>
 
+/*
+ * The irq entry code is in the noinstr section and the start/end of
+ * __irqentry_text is emitted via labels. Make the build fail if
+ * something moves a C function into the __irq_entry section.
+ */
+#define __irq_entry __invalid_section
+
 static inline int irq_canonicalize(int irq)
 {
 	return ((irq == 2) ? 9 : irq);

arch/x86/kernel/kprobes/core.c

@@ -1073,13 +1073,6 @@ NOKPROBE_SYMBOL(kprobe_fault_handler);
 
 int __init arch_populate_kprobe_blacklist(void)
 {
-	int ret;
-
-	ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
-					 (unsigned long)__irqentry_text_end);
-	if (ret)
-		return ret;
-
 	return kprobe_add_area_blacklist((unsigned long)__entry_text_start,
 					 (unsigned long)__entry_text_end);
 }

arch/x86/kernel/kprobes/opt.c

@@ -286,9 +286,7 @@ static int can_optimize(unsigned long paddr)
 	 * stack handling and registers setup.
 	 */
 	if (((paddr >= (unsigned long)__entry_text_start) &&
-	     (paddr <  (unsigned long)__entry_text_end)) ||
-	    ((paddr >= (unsigned long)__irqentry_text_start) &&
-	     (paddr <  (unsigned long)__irqentry_text_end)))
+	     (paddr <  (unsigned long)__entry_text_end)))
 		return 0;
 
 	/* Check there is enough space for a relative jump. */

arch/x86/kernel/unwind_frame.c

@@ -74,13 +74,7 @@ static bool in_entry_code(unsigned long ip)
 {
 	char *addr = (char *)ip;
 
-	if (addr >= __entry_text_start && addr < __entry_text_end)
-		return true;
-
-	if (addr >= __irqentry_text_start && addr < __irqentry_text_end)
-		return true;
-
-	return false;
+	return addr >= __entry_text_start && addr < __entry_text_end;
 }
 
 static inline unsigned long *last_frame(struct unwind_state *state)

arch/x86/kernel/vmlinux.lds.S

@@ -134,7 +134,6 @@ SECTIONS
 		KPROBES_TEXT
 		ALIGN_ENTRY_TEXT_BEGIN
 		ENTRY_TEXT
-		IRQENTRY_TEXT
 		ALIGN_ENTRY_TEXT_END
 		SOFTIRQENTRY_TEXT
 		*(.fixup)

arch/x86/mm/pti.c

@@ -492,12 +492,12 @@ static void __init pti_setup_espfix64(void)
 }
 
 /*
- * Clone the populated PMDs of the entry and irqentry text and force it RO.
+ * Clone the populated PMDs of the entry text and force it RO.
  */
 static void pti_clone_entry_text(void)
 {
 	pti_clone_pgtable((unsigned long) __entry_text_start,
-			  (unsigned long) __irqentry_text_end,
+			  (unsigned long) __entry_text_end,
 			  PTI_CLONE_PMD);
 }
 

include/linux/interrupt.h

@@ -760,8 +760,10 @@ extern int arch_early_irq_init(void);
 /*
  * We want to know which function is an entrypoint of a hardirq or a softirq.
  */
-#define __irq_entry		 __attribute__((__section__(".irqentry.text")))
-#define __softirq_entry  \
-	__attribute__((__section__(".softirqentry.text")))
+#ifndef __irq_entry
+# define __irq_entry	 __attribute__((__section__(".irqentry.text")))
+#endif
+
+#define __softirq_entry  __attribute__((__section__(".softirqentry.text")))
 
 #endif