[tip:x86/apic] x86/idt: Fix the X86_TRAP_BP gate

[tip-bot for Ingo Molnar]

Commit-ID:  c6ef89421e236d75693ae968d80d44a52409889d
Gitweb:     http://git.kernel.org/tip/c6ef89421e236d75693ae968d80d44a52409889d
Author:     Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Fri, 1 Sep 2017 11:04:56 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 1 Sep 2017 11:04:56 +0200

x86/idt: Fix the X86_TRAP_BP gate

Andrei Vagin reported a CRIU regression and bisected it back to:

  90f6225fba0c ("x86/idt: Move IST stack based traps to table init")

This table init conversion loses the system-gate property of X86_TRAP_BP
and erroneously moves it from DPL3 to DPL0.

Fix it.

Reported-by: Andrei Vagin <avagin@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: dvlasenk@xxxxxxxxxx
Cc: linux-tip-commits@xxxxxxxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: brgerst@xxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: bp@xxxxxxxxx
Cc: luto@xxxxxxxxxx
Cc: jpoimboe@xxxxxxxxxx
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
Cc: tip-bot for Jacob Shin <tipbot@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20170901082630.xvyi5bwk6etmppqc@xxxxxxxxx

---
 arch/x86/kernel/idt.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 61b490c..6107ee1 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -44,6 +44,10 @@ struct idt_data {
 #define ISTG(_vector, _addr, _ist)			\
 	G(_vector, _addr, _ist, GATE_INTERRUPT, DPL0, __KERNEL_CS)
 
+/* System interrupt gate with interrupt stack */
+#define SISTG(_vector, _addr, _ist)			\
+	G(_vector, _addr, _ist, GATE_INTERRUPT, DPL3, __KERNEL_CS)
+
 /* Task gate */
 #define TSKG(_vector, _gdt)				\
 	G(_vector, NULL, DEFAULT_STACK, GATE_TASK, DPL0, _gdt << 3)
@@ -181,7 +185,7 @@ gate_desc debug_idt_table[IDT_ENTRIES] __page_aligned_bss;
 static const __initdata struct idt_data ist_idts[] = {
 	ISTG(X86_TRAP_DB,	debug,		DEBUG_STACK),
 	ISTG(X86_TRAP_NMI,	nmi,		NMI_STACK),
-	ISTG(X86_TRAP_BP,	int3,		DEBUG_STACK),
+	SISTG(X86_TRAP_BP,	int3,		DEBUG_STACK),
 	ISTG(X86_TRAP_DF,	double_fault,	DOUBLEFAULT_STACK),
 #ifdef CONFIG_X86_MCE
 	ISTG(X86_TRAP_MC,	&machine_check,	MCE_STACK),