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>

1 files changed, 1 insertions, 3 deletions

diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 234f58e0fe8c..321c19950285 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/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. */