[PATCH] i386: NMI <-> debugging handler adjustments

["Jan Beulich" <JBeulich@novell.com>]

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Also account for an INT3 breakpoint potentially placed (from a kernel
debugger) on sysenter_entry, which requires the NMI handler to add one
more check. Further, don't discard debug or breakpoint traps/faults
happening on this one instruction and their handler getting
interrupted by an NMI before being able to fix the stack.

From: Jan Beulich <jbeulich@novell.com>

(actual patch attached)


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Also account for an INT3 breakpoint potentially placed (from a kernel
debugger) on sysenter_entry, which requires the NMI handler to add one
more check. Further, don't discard debug or breakpoint traps/faults
happening on this one instruction and their handler getting
interrupted by an NMI before being able to fix the stack.

From: Jan Beulich <jbeulich@novell.com>

--- 2.6.14/arch/i386/kernel/entry.S	2005-10-28 02:02:08.000000000 +0200
+++ 2.6.14-i386-nmi-int3/arch/i386/kernel/entry.S	2005-11-08 17:06:59.000000000 +0100
@@ -178,6 +178,7 @@ need_resched:
 	# sysenter call handler stub
 ENTRY(sysenter_entry)
 	movl TSS_sysenter_esp0(%esp),%esp
+.globl sysenter_past_esp
 sysenter_past_esp:
 	sti
 	pushl $(__USER_DS)
@@ -520,12 +521,12 @@ debug_stack_correct:
 	jmp ret_from_exception
 	.previous .text
 /*
- * NMI is doubly nasty. It can happen _while_ we're handling
- * a debug fault, and the debug fault hasn't yet been able to
- * clear up the stack. So we first check whether we got  an
+ * NMI is doubly nasty. It can happen _while_ we're handling a debug
+ * fault or breakpoint trap, and the fault/trap hasn't yet been able
+ * to clear up the stack. So we first check whether we got an
  * NMI on the sysenter entry path, but after that we need to
- * check whether we got an NMI on the debug path where the debug
- * fault happened on the sysenter path.
+ * check whether we got an NMI on the debug/breakpoint path where the
+ * fault/trap happened on the sysenter path.
  */
 ENTRY(nmi)
 	pushl %eax
@@ -546,6 +547,8 @@ ENTRY(nmi)
 	jae nmi_stack_correct
 	cmpl $sysenter_entry,12(%esp)
 	je nmi_debug_stack_check
+	cmpl $sysenter_entry+1,12(%esp)
+	je .Lnmi_int3_stack_check
 nmi_stack_correct:
 	pushl %eax
 	SAVE_ALL
@@ -566,6 +569,21 @@ nmi_debug_stack_check:
 	jle nmi_debug_stack_fixup
 nmi_debug_stack_fixup:
 	FIX_STACK(24,nmi_stack_correct, 1)
+	pushfl
+	pushl $__KERNEL_CS
+	pushl $debug_stack_correct
+	jmp nmi_stack_correct
+.Lnmi_int3_stack_check:
+	cmpw $__KERNEL_CS,16(%esp)
+	jne nmi_stack_correct
+	cmpl $int3, (%esp)
+	jb nmi_stack_correct
+	cmpl $.Lint3_esp_fix_insn, (%esp)
+	ja nmi_stack_correct
+	FIX_STACK(24,nmi_stack_correct, 1)
+	pushfl
+	pushl $__KERNEL_CS
+	pushl $.Lint3_stack_correct
 	jmp nmi_stack_correct
 
 nmi_16bit_stack:
@@ -592,6 +610,10 @@ nmi_16bit_stack:
 .previous
 
 KPROBE_ENTRY(int3)
+	cmpl $sysenter_entry+1, (%esp)
+	jne .Lint3_stack_correct
+	FIX_STACK(12, .Lint3_stack_correct, .Lint3_esp_fix_insn)
+.Lint3_stack_correct:
 	pushl $-1			# mark this as an int
 	SAVE_ALL
 	xorl %edx,%edx		# zero error code