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

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Date:	Fri, 15 Feb 2013 11:02:49 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Paul Moore <pmoore@...hat.com>
CC:	x86@...nel.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 02/15/2013 09:21 AM, 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.
> 

Hi... it isn't 100% clear from the description if you have audited *all*
the callers?

	-hpa


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