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Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the fast path

From "H. Peter Anvin" <hpa@zytor.com>
Newsgroups linux.kernel
Subject Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the fast path
Date 2016-04-18 07:00 +0200
Message-ID <rp9rY-863-5@gated-at.bofh.it> (permalink)
References <rp5y1-4CY-7@gated-at.bofh.it> <rp5y1-4CY-9@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On 04/17/16 17:47, Ben Hutchings wrote:
> We've always masked off the top 32 bits when x32 is enabled, but
> hopefully no-one relies on that.  Now that the slow path is in C, we
> check all the bits there, regardless of whether x32 is enabled.  Let's
> make the fast path consistent with it.

We have always masked off the top 32 bits *period*.

We have had some bugs where we haven't, because someone has tried to
"optimize" the code and they have been quite serious.  The system call
number is an int, which means the upper 32 bits are undefined on call
entry: we HAVE to mask them.

	-hpa

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Re: System call number masking Ben Hutchings <ben@decadent.org.uk> - 2016-04-18 02:50 +0200
  [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path Ben Hutchings <ben@decadent.org.uk> - 2016-04-18 02:50 +0200
    Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path "H. Peter Anvin" <hpa@zytor.com> - 2016-04-18 07:00 +0200
      Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path Andy Lutomirski <luto@amacapital.net> - 2016-04-18 07:20 +0200
        Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path "H. Peter Anvin" <hpa@zytor.com> - 2016-04-18 07:30 +0200
        Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path "H. Peter Anvin" <hpa@zytor.com> - 2016-04-18 07:30 +0200
          Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path Andy Lutomirski <luto@amacapital.net> - 2016-04-18 07:40 +0200
            Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path "H. Peter Anvin" <hpa@zytor.com> - 2016-04-18 07:50 +0200
              Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path Andy Lutomirski <luto@amacapital.net> - 2016-04-18 07:50 +0200
                Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path "H. Peter Anvin" <hpa@zytor.com> - 2016-04-18 08:10 +0200
                Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path "H. Peter Anvin" <hpa@zytor.com> - 2016-04-18 08:20 +0200
                Re: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the  fast path Andy Lutomirski <luto@amacapital.net> - 2016-04-18 08:20 +0200

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