linux-kernel - Re: [PATCH 1/3] x86/perf/hw_breakpoint: Disallow kernel breakpoints unless kprobe-safe

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Date:	Tue, 1 Sep 2015 12:57:11 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	X86 ML <x86@...nel.org>
Subject: Re: [PATCH 1/3] x86/perf/hw_breakpoint: Disallow kernel breakpoints
 unless kprobe-safe

2015-08-05 1:29 GMT+02:00 平松雅巳 / HIRAMATU，MASAMI
<masami.hiramatsu.pt@...achi.com>:
> Hi,
>
>> From: Frederic Weisbecker [mailto:fweisbec@...il.com]
>>
>> On Thu, Jul 30, 2015 at 08:32:40PM -0700, Andy Lutomirski wrote:
>> > Code on the kprobe blacklist doesn't want unexpected int3
>> > exceptions.  It probably doesn't want unexpected debug exceptions
>> > either.  Be safe: disallow breakpoints in nokprobes code.
>> >
>> > On non-CONFIG_KPROBES kernels, there is no kprobe blacklist.  In
>> > that case, disallow kernel breakpoints entirely.
>> >
>> > It will be particularly important to keep hw breakpoints out of the
>> > entry and NMI code once we move debug exceptions off the IST stack.
>> >
>> > Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> > ---
>> >  arch/x86/kernel/hw_breakpoint.c | 15 +++++++++++++++
>> >  include/linux/kprobes.h         |  2 ++
>> >  kernel/kprobes.c                |  2 +-
>> >  3 files changed, 18 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
>> > index 7114ba220fd4..78f3e90c5659 100644
>> > --- a/arch/x86/kernel/hw_breakpoint.c
>> > +++ b/arch/x86/kernel/hw_breakpoint.c
>> > @@ -32,6 +32,7 @@
>> >  #include <linux/irqflags.h>
>> >  #include <linux/notifier.h>
>> >  #include <linux/kallsyms.h>
>> > +#include <linux/kprobes.h>
>> >  #include <linux/percpu.h>
>> >  #include <linux/kdebug.h>
>> >  #include <linux/kernel.h>
>> > @@ -243,6 +244,20 @@ static int arch_build_bp_info(struct perf_event *bp)
>> >             info->type = X86_BREAKPOINT_RW;
>> >             break;
>> >     case HW_BREAKPOINT_X:
>> > +           /*
>> > +            * We don't allow kernel breakpoints in places that are not
>> > +            * acceptable for kprobes.  On non-kprobes kernels, we don't
>> > +            * allow kernel breakpoints at all.
>> > +            */
>> > +           if (bp->attr.bp_addr >= TASK_SIZE_MAX) {
>> > +#ifdef CONFIG_KPROBES
>> > +                   if (within_kprobe_blacklist(bp->attr.bp_addr))
>> > +                           return -EINVAL;
>> > +#else
>> > +                   return -EINVAL;
>> > +#endif
>> > +           }
>> > +
>>
>> It should be done on generic code I think. In validate_hw_breakpoint()
>> under the arch_check_bp_in_kernelspace() check.
>
> Agreed, kprobes also does it in generic code.

Well, the patchset got applied anyway and the reviews ignored...
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