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    SubjectRe: [PATCH] x86/idt: Fix the X86_TRAP_BP gate
    On Fri, 1 Sep 2017, Ingo Molnar wrote:
    > Subject: x86/idt: Fix the X86_TRAP_BP gate
    > From: Ingo Molnar <mingo@kernel.org>
    >
    > 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.

    Duh, yes. Thanks for spotting it.

    > Fix it.
    >
    > Reported-by: Andrei Vagin <avagin@virtuozzo.com>
    > Cc: Linus Torvalds <torvalds@linux-foundation.org>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Signed-off-by: Ingo Molnar <mingo@kernel.org>
    > ---
    > arch/x86/kernel/idt.c | 6 +++++-
    > arch/x86/kernel/idt.c | 6 +++++-
    > 1 file changed, 5 insertions(+), 1 deletion(-)
    >
    > Index: tip/arch/x86/kernel/idt.c
    > ===================================================================
    > --- tip.orig/arch/x86/kernel/idt.c
    > +++ tip/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] _
    > 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),
    >

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