linux-kernel - Re: [PATCH] x32: Mask away the x32 syscall bit in the ptrace codepath

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Date:	Wed, 28 May 2014 15:37:17 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Philipp Kern <pkern@...gle.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. J. Lu" <hjl.tools@...il.com>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH] x32: Mask away the x32 syscall bit in the ptrace codepath

On 05/28/2014 02:53 PM, Philipp Kern wrote:
> On Wed, May 28, 2014 at 11:43 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> However: are you sure that entry_64.S handles this?  It looks like
>> tracesys has higher priority than badsys.  And strace can certainly
>> see out-of-range syscalls. […]
> 
> Not only can it see them: It must see that this bit is set as that's
> the only identifier it has to deduce that the binary is running in x32
> mode.

Yes... keep in mind the ABI is a local property: just because the binary
is running in x32 mode doesn't mean it can't access x86-64 or i386
system calls (or similar for x86-64 processes.)  A process started in
i386 mode can transition to long mode and execute x86-64 or x32 system
calls, too.

	-hpa

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