Re: [PATCH] x86/refcount: Implement fast refcount_t handling

From	"PaX Team" <pageexec@freemail.hu>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86/refcount: Implement fast refcount_t handling
Date	2017-04-25 13:30 +0200
Message-ID	<tA6Po-420-9@gated-at.bofh.it> (permalink)
References	<tzK2u-6io-9@gated-at.bofh.it> <tA5Tl-3rD-47@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 25 Apr 2017 at 12:23, Peter Zijlstra wrote:

> So what avoids this:

simple, you noted it yourself in your previous mail:

> Well, your setup (panic_on_warn et al) would have it panic the box. That
> will effectively stop the exploit by virtue of stopping everything.

with that in mind the actual code looks like this:

>	CPU0				CPU1
>
>
>	lock inc %[val]; # 0x7fffffff
>	jo  2f
>1:	...
>
>					lock dec %[val]; # 0x80000000
>					jo  2f
>				1:	...
>
>
>
>
>2:	mov $0x7fffffff, %[val]

	panic()

>	jmp 1b
>
>				2:	mov $0x80000000, %[val]

					panic()

>					jmp 1b
>

... and we never get this far.

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[PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-22 00:10 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 10:40 +0200
    Re: [kernel-hardening] Re: [PATCH] x86/refcount: Implement fast  refcount_t handling Jann Horn <jannh@google.com> - 2017-04-24 11:00 +0200
      Re: [kernel-hardening] Re: [PATCH] x86/refcount: Implement fast  refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 11:30 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-24 13:10 +0200
      Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 13:20 +0200
        Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-24 15:20 +0200
          Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 15:40 +0200
            Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-24 17:20 +0200
              Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:50 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-25 00:10 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-25 00:40 +0200
                Re: [kernel-hardening] Re: [PATCH] x86/refcount: Implement fast  refcount_t handling Rik van Riel <riel@redhat.com> - 2017-04-25 03:20 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-25 11:10 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-25 13:30 +0200
                Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-25 18:40 +0200
      Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:40 +0200
        Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-25 13:30 +0200
          Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-25 18:50 +0200
            Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-26 04:20 +0200
              Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-26 06:50 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:20 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 12:50 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:20 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-24 13:00 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling Kees Cook <keescook@chromium.org> - 2017-04-24 22:30 +0200
  Re: [PATCH] x86/refcount: Implement fast refcount_t handling Peter Zijlstra <peterz@infradead.org> - 2017-04-25 12:30 +0200
    Re: [PATCH] x86/refcount: Implement fast refcount_t handling "PaX Team" <pageexec@freemail.hu> - 2017-04-25 13:30 +0200

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