Re: [PATCH] x86/idt: Fix the X86_TRAP_BP gate

Andrei Vagin
2017-09-01T14:40:15Z

On Fri, Sep 01, 2017 at 10:26:30AM +0200, Ingo Molnar wrote:
>
> Hi Andrei,
>
> * Andrei Vagin <avagin@virtuozzo.com> wrote:
>
> > Hi Thomas,
> >
> > We run CRIU tests for linux-next and today they detected an issue. I've
> > bisected this problem and it looks like a problem is in this patch.
>
> Ok, there appears to be a bug in that conversion - does the patch below fix the
> regression for you?

Yes, it is.

Thank you!

>
> Thanks,
>
> Ingo
>
> ================================>
> 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.
>
> 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),