x86/entry/64: Update comments and sanity tests for create_gap

Commit 2700fefdb2d9 ("x86_64: Add gap to int3 to allow for call
emulation") forgot to update the comment, do so now.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: bp@alien8.de
Cc: torvalds@linux-foundation.org
Cc: hpa@zytor.com
Cc: dave.hansen@linux.intel.com
Cc: jgross@suse.com
Cc: zhe.he@windriver.com
Cc: joel@joelfernandes.org
Cc: devel@etsukata.com
Link: https://lkml.kernel.org/r/20190711114336.059780563@infradead.org

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 3db5fede743b7d52910b7698021a077bc9df019e..95ae05f0edf2c3cb36441c8fb3fc3496e1e5636c 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -913,15 +913,16 @@ apicinterrupt IRQ_WORK_VECTOR                     irq_work_interrupt              smp_irq_work_interrupt
 /**
  * idtentry - Generate an IDT entry stub
  * @sym:               Name of the generated entry point
- * @do_sym:            C function to be called
- * @has_error_code:    True if this IDT vector has an error code on the stack
- * @paranoid:          non-zero means that this vector may be invoked from
+ * @do_sym:            C function to be called
+ * @has_error_code:    True if this IDT vector has an error code on the stack
+ * @paranoid:          non-zero means that this vector may be invoked from
  *                     kernel mode with user GSBASE and/or user CR3.
  *                     2 is special -- see below.
  * @shift_ist:         Set to an IST index if entries from kernel mode should
- *                             decrement the IST stack so that nested entries get a
+ *                     decrement the IST stack so that nested entries get a
  *                     fresh stack.  (This is for #DB, which has a nasty habit
- *                             of recursing.)
+ *                     of recursing.)
+ * @create_gap:                create a 6-word stack gap when coming from kernel mode.
  *
  * idtentry generates an IDT stub that sets up a usable kernel context,
  * creates struct pt_regs, and calls @do_sym.  The stub has the following
@@ -951,10 +952,14 @@ ENTRY(\sym)
        UNWIND_HINT_IRET_REGS offset=\has_error_code*8
 
        /* Sanity check */
-       .if \shift_ist != -1 && \paranoid == 0
+       .if \shift_ist != -1 && \paranoid != 1
        .error "using shift_ist requires paranoid=1"
        .endif
 
+       .if \create_gap && \paranoid
+       .error "using create_gap requires paranoid=0"
+       .endif
+
        ASM_CLAC
 
        .if \has_error_code == 0