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From: "H.J. Lu" <>
To: "H. Peter Anvin" <>
Cc: Paul Moore <>,,,,,
Subject: Re: [PATCH] x86: remove the x32 syscall bitmask from syscall_get_nr()
Date: Fri, 15 Mar 2013 15:18:12 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Mar 15, 2013 at 2:56 PM, H. Peter Anvin <> wrote:
> On 03/15/2013 02:15 PM, Paul Moore wrote:
>> On Tuesday, February 26, 2013 03:58:23 PM Paul Moore wrote:
>>> On Friday, February 15, 2013 12:21:43 PM Paul Moore wrote:
>>>> Commit fca460f95e928bae373daa8295877b6905bc62b8 simplified the x32
>>>> implementation by creating a syscall bitmask, equal to 0x40000000, that
>>>> could be applied to x32 syscalls such that the masked syscall number
>>>> would be the same as a x86_64 syscall.  While that patch was a nice
>>>> way to simplify the code, it went a bit too far by adding the mask to
>>>> syscall_get_nr(); returning the masked syscall numbers can cause
>>>> confusion with callers that expect syscall numbers matching the x32
>>>> ABI, e.g. unmasked syscall numbers.
>>>> This patch fixes this by simply removing the mask from syscall_get_nr()
>>>> while preserving the other changes from the original commit.  While
>>>> there are several syscall_get_nr() callers in the kernel, most simply
>>>> check that the syscall number is greater than zero, in this case this
>>>> patch will have no effect.  Of those remaining callers, they appear
>>>> to be few, seccomp and ftrace, and from my testing of seccomp without
>>>> this patch the original commit definitely breaks things; the seccomp
>>>> filter does not correctly filter the syscalls due to the difference in
>>>> syscall numbers in the BPF filter and the value from syscall_get_nr().
>>>> Applying this patch restores the seccomp BPF filter functionality on
>>>> x32.
>>>> I've tested this patch with the seccomp BPF filters as well as ftrace
>>>> and everything looks reasonable to me; needless to say general usage
>>>> seemed fine as well.
>>> I just wanted to check and see where things stood with this patch.  I'm not
>>> overly concerned about how this problem is solved, just that it is solved.
>>> If someone else has a better approach that is fine with me; I'll even make
>>> the offer to do additional testing if needed.
>> Anyone?  The seccomp filter bits are completely broken on x32 and I'd like to
>> get this fixed, if not with this patch then something else - I'm more than
>> happy to test/verify/etc whatever solution is deemed best ...
> Seems good to me -- H.J., do you seen any problem with this?

It looks OK to me.


  reply	other threads:[~2013-03-15 22:18 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-02-15 17:21 Paul Moore
2013-02-15 19:02 ` H. Peter Anvin
2013-02-15 20:52   ` Paul Moore
2013-02-26 20:58 ` Paul Moore
2013-03-15 21:15   ` Paul Moore
2013-03-15 21:56     ` H. Peter Anvin
2013-03-15 22:18       ` H.J. Lu [this message]
2013-03-25 20:55         ` Paul Moore
2013-04-02 21:31           ` Paul Moore
2013-04-03  0:17 ` [tip:x86/urgent] " tip-bot for Paul Moore

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