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SubjectRe: [BUG 4.2-rc8] Interrupt occurs while apply_alternatives() is patching the handler
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On Thu, Sep 3, 2015 at 6:41 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Thu, 3 Sep 2015, Borislav Petkov wrote:
>> On Wed, Sep 02, 2015 at 11:11:55AM +0200, Thomas Gleixner wrote:
>> > static void __init_or_module add_nops(void *insns, unsigned int len)
>> > {
>> > + unsigned long flags;
>> > +
>> > + local_irq_save(flags);
>> > while (len > 0) {
>>
>> I guess you want to optimize the len==0 case to not disable interrupts
>> needlessly:
>>
>> if (!len)
>> return;
>>
>> local_irq_save(flags);
>> while (len > 0)
>> ...
>
> Nah. I rather put the local_irq_save into optimize_nops(). All other
> callers of add_nops() are operating on a buffer and use text_poke
> after that. Aside of that optimize_nops() is missing a sync_core().
>
> Updated patch below.
>
> Thanks,
>
> tglx
>
> ----------------->
> Subject: x86/alternatives: Make optimize_nops() interrupt safe and synced
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Thu, 03 Sep 2015 12:34:55 +0200
>
> optimize_nops() is buggy in two aspects:
>
> - It's not disabling interrupts across the modification
> - It's lacking a sync_core() call
>
> Fixes: 4fd4b6e5537c 'x86/alternatives: Use optimized NOPs for padding'

Possibly CC: stable since it fixes a commit in 4.1 and 4.2?

josh

> Reported-by: "Richard W.M. Jones" <rjones@redhat.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/kernel/alternative.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> Index: tip/arch/x86/kernel/alternative.c
> ===================================================================
> --- tip.orig/arch/x86/kernel/alternative.c
> +++ tip/arch/x86/kernel/alternative.c
> @@ -338,10 +338,15 @@ done:
>
> static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr)
> {
> + unsigned long flags;
> +
> if (instr[0] != 0x90)
> return;
>
> + local_irq_save(flags);
> add_nops(instr + (a->instrlen - a->padlen), a->padlen);
> + sync_core();
> + local_irq_restore(flags);
>
> DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ",
> instr, a->instrlen - a->padlen, a->padlen);
>
>
> --
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