linux-kernel - Re: [PATCH] x86: remove the x32 syscall bitmask from syscall_get

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Message-ID: <CAMe9rOriYUYVmef36PVuZn5LWtthryj3n7vRzXRObC_ZkcVuqQ@mail.gmail.com>
Date:	Fri, 15 Mar 2013 15:18:12 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Paul Moore <pmoore@...hat.com>, x86@...nel.org,
	keescook@...omium.org, linux-kernel@...r.kernel.org,
	coreyb@...ux.vnet.ibm.com, wad@...omium.org
Subject: Re: [PATCH] x86: remove the x32 syscall bitmask from syscall_get_nr()

On Fri, Mar 15, 2013 at 2:56 PM, H. Peter Anvin <hpa@...or.com> 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.

-- 
H.J.
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