[tboot-devel] [PATCH] Correct IDT exception handler addresses

[Alex O. <thi...@gm...>]

# HG changeset patch
# User Alex Olson <ale...@st...>
# Date 1657558891 18000
#      Mon Jul 11 12:01:31 2022 -0500
# Node ID 0552b7ac10e28b378dd139e5ca3838039c472827
# Parent  fa60b63892e8f9d4278950b44ed136d2b12d19cc
Correct IDT exception handler addresses

The exception handlers configured in the IDT weren't properly executed
during exceptions as _start/TBOOT_START are not 64K aligned (0x804000).

This revision corrects the arithmetic so that the "int_handler" routine
gets properly executed instead of "int_handler - 0x4000".

NOTE: A simple way to test this is to insert 'asm volatile("ud2");' in begin_launch().

Signed-off-by: Alex Olson <ale...@st...>

diff -r fa60b63892e8 -r 0552b7ac10e2 tboot/common/boot.S
--- a/tboot/common/boot.S	Fri Jun 17 11:39:11 2022 +0300
+++ b/tboot/common/boot.S	Mon Jul 11 12:01:31 2022 -0500
@@ -400,23 +400,28 @@
 
 	.align	8
 
+/* Below assumes "_start" is exactly at TBOOT_START and is needed to allow arithmetic: */
+#define INT_HANDLER_ADDR   (int_handler - _start + TBOOT_START)
+#define INT_HANDLER_LO16   (INT_HANDLER_ADDR & 0xffff)
+#define INT_HANDLER_HI16   (INT_HANDLER_ADDR >> 16)
+
 idt_table:
 	.rept 18
-		.word	int_handler - _start
+		.word	INT_HANDLER_LO16
 		.word	cs_sel
 		.word	0x8e00   /* present, DPL=0, 32b, interrupt */
-		.word	(int_handler - _start + TBOOT_START) >> 16
+		.word	INT_HANDLER_HI16
 	.endr
 	/* for machine-check exception */
-		.word	int_handler - _start
+		.word	INT_HANDLER_LO16
 		.word	cs_sel
 		.word	0x8f00   /* present, DPL=0, 32b, trap */
-		.word	(int_handler - _start + TBOOT_START) >> 16
+		.word	INT_HANDLER_HI16
 	.rept 237
-		.word	int_handler - _start
+		.word	INT_HANDLER_LO16
 		.word	cs_sel
 		.word	0x8e00   /* present, DPL=0, 32b, interrupt */
-		.word	(int_handler - _start + TBOOT_START) >> 16
+		.word	INT_HANDLER_HI16
 	.endr
 idt_table_end: