From 8b29b18fda413928c32473475ca51aa05c52db18 Mon Sep 17 00:00:00 2001
From: Luca Dariz <luca@orpolo.org>
Date: Sat, 29 Jul 2023 19:45:14 +0200
Subject: x86_64: install emergency handler for double fault

* i386/i386/idt.c: add selector for the interrupt-specific stack
* i386/i386/ktss.c: configure ist1 to use a dedicated stack
* i386/i386/trap.c: add double fault handler, which just prints the
  state and panics. There is not much else to do in this case but it's
  useful for troubleshooting
* x86_64/idt_inittab.S: allow to specify an interrupt stack for custom
  handlers
* x86_64/locore.S: add double fault handler
Message-Id: <20230729174514.1145656-1-luca@orpolo.org>
---
 x86_64/idt_inittab.S | 25 +++++++++++++------------
 x86_64/locore.S      | 15 +++++++++++++++
 2 files changed, 28 insertions(+), 12 deletions(-)

(limited to 'x86_64')

diff --git a/x86_64/idt_inittab.S b/x86_64/idt_inittab.S
index f021b56d..fc1df0c7 100644
--- a/x86_64/idt_inittab.S
+++ b/x86_64/idt_inittab.S
@@ -50,12 +50,13 @@ ENTRY(idt_inittab)
 	.quad	entry		;\
 	.text
 #else	/* MACH_PV_DESCRIPTORS */
-#define	IDT_ENTRY(n,entry,type) \
+#define	IDT_ENTRY(n,entry,type,ist) \
 	.data	2		;\
 	.quad	entry		;\
 	.word	n		;\
 	.word	type		;\
-	.long	0	/*pad*/	;\
+	.word	ist		;\
+	.word	0	/*pad*/	;\
 	.text
 #endif	/* MACH_PV_DESCRIPTORS */
 
@@ -63,7 +64,7 @@ ENTRY(idt_inittab)
  * No error code.  Clear error code and push trap number.
  */
 #define	EXCEPTION(n,name) \
-	IDT_ENTRY(n,EXT(name),ACC_PL_K|ACC_TRAP_GATE);\
+	IDT_ENTRY(n,EXT(name),ACC_PL_K|ACC_TRAP_GATE, 0);\
 ENTRY(name)				;\
 	INT_FIX				;\
 	pushq	$(0)			;\
@@ -74,7 +75,7 @@ ENTRY(name)				;\
  * User-accessible exception.  Otherwise, same as above.
  */
 #define	EXCEP_USR(n,name) \
-	IDT_ENTRY(n,EXT(name),ACC_PL_U|ACC_TRAP_GATE);\
+	IDT_ENTRY(n,EXT(name),ACC_PL_U|ACC_TRAP_GATE, 0);\
 ENTRY(name)				;\
 	INT_FIX				;\
 	pushq	$(0)			;\
@@ -85,7 +86,7 @@ ENTRY(name)				;\
  * Error code has been pushed.  Just push trap number.
  */
 #define	EXCEP_ERR(n,name) \
-	IDT_ENTRY(n,EXT(name),ACC_PL_K|ACC_INTR_GATE);\
+	IDT_ENTRY(n,EXT(name),ACC_PL_K|ACC_INTR_GATE, 0);\
 ENTRY(name)				;\
 	INT_FIX				;\
 	pushq	$(n)			;\
@@ -95,25 +96,25 @@ ENTRY(name)				;\
  * Special interrupt code: dispatches to a unique entrypoint,
  * not defined automatically here.
  */
-#define	EXCEP_SPC(n,name)  \
-	IDT_ENTRY(n,EXT(name),ACC_PL_K|ACC_TRAP_GATE)
+#define	EXCEP_SPC(n,name, ist)  \
+	IDT_ENTRY(n,EXT(name),ACC_PL_K|ACC_TRAP_GATE, ist)
 
 
 EXCEPTION(0x00,t_zero_div)
-EXCEP_SPC(0x01,t_debug)
+EXCEP_SPC(0x01,t_debug, 0)
 /* skip NMI interrupt - let more specific code figure that out.  */
 EXCEP_USR(0x03,t_int3)
 EXCEP_USR(0x04,t_into)
 EXCEP_USR(0x05,t_bounds)
 EXCEPTION(0x06,t_invop)
 EXCEPTION(0x07,t_nofpu)
-EXCEPTION(0x08,a_dbl_fault)
+EXCEP_SPC(0x08,t_dbl_fault, 1)
 EXCEPTION(0x09,a_fpu_over)
 EXCEPTION(0x0a,a_inv_tss)
-EXCEP_SPC(0x0b,t_segnp)
+EXCEP_SPC(0x0b,t_segnp, 0)
 EXCEP_ERR(0x0c,t_stack_fault)
-EXCEP_SPC(0x0d,t_gen_prot)
-EXCEP_SPC(0x0e,t_page_fault)
+EXCEP_SPC(0x0d,t_gen_prot, 0)
+EXCEP_SPC(0x0e,t_page_fault, 0)
 #ifdef MACH_PV_DESCRIPTORS
 EXCEP_ERR(0x0f,t_trap_0f)
 #else
diff --git a/x86_64/locore.S b/x86_64/locore.S
index 2938e430..16b0dde5 100644
--- a/x86_64/locore.S
+++ b/x86_64/locore.S
@@ -345,6 +345,21 @@ ENTRY(start_timer)
  *
  */
 
+/* Try to save/show some information when a double fault happens
+ * We can't recover to a working state, so if we have a debugger wait for it,
+ * otherwise reset */
+ENTRY(t_dbl_fault)
+	INT_FIX
+	cli	/* disable interrupts that might corrupt the state*/
+	pusha
+	movq	%cr2,%rax
+	movq	%rax,R_CR2-R_R15(%rsp)	/* CR2 might contain the faulting address */
+	subq	$48,%rsp	// FIXME remove when segments are cleaned up
+	movq	%rsp,%rdi		/* pass the saved state */
+	call	handle_double_fault
+	jmp	cpu_shutdown	/* reset */
+END(t_dbl_fault)
+
 /*
  * General protection or segment-not-present fault.
  * Check for a GP/NP fault in the kernel_return
-- 
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