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From: Richard Weinberger <richard@nod.at>
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Date: Mon, 21 Dec 2015 09:56:35 +0100
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Subject: Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs
To: =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@digikod.net>, linux-kernel@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>, Jeff Dike <jdike@addtoit.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org, Kees Cook <keescook@chromium.org>, Andy Lutomirski <luto@amacapital.net>, Will Drewry <wad@chromium.org>, Shuah Khan <shuahkh@osg.samsung.com>, Chris Metcalf <cmetcalf@ezchip.com>, Michael Ellerman <mpe@ellerman.id.au>, Andrew Morton <akpm@linux-foundation.org>, James Hogan <james.hogan@imgtec.com>, Thomas Meyer <thomas@m3y3r.de>, Nicolas Iooss <nicolas.iooss_linux@m4x.org>, Anton Ivanov <aivanov@brocade.com>, linux-doc@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, linux-api@vger.kernel.org, Meredydd Luff <meredydd@senatehouse.org>, David Drysdale <drysdale@google.com>
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Hi!

Am 21.12.2015 um 09:49 schrieb Micka=C3=ABl Sala=C3=BCn:
>=20
> On 21/12/2015 01:20, Richard Weinberger wrote:
>> Am 21.12.2015 um 01:03 schrieb Micka=C3=ABl Sala=C3=BCn:
>>> diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/sy=
scall.c
>>> index 1683b8e..65f0d1a 100644
>>> --- a/arch/um/kernel/skas/syscall.c
>>> +++ b/arch/um/kernel/skas/syscall.c
>>> @@ -7,6 +7,7 @@
>>>  #include <linux/ptrace.h>
>>>  #include <kern_util.h>
>>>  #include <sysdep/ptrace.h>
>>> +#include <sysdep/ptrace_user.h>
>>>  #include <sysdep/syscalls.h>
>>>  #include <os.h>
>>> =20
>>> @@ -16,12 +17,16 @@ void handle_syscall(struct uml_pt_regs *r)
>>>  	long result;
>>>  	int syscall;
>>> =20
>>> +	/* Save the syscall register. */
>>> +	UPT_SYSCALL_NR(r) =3D PT_SYSCALL_NR(r->gp);
>>> +
>>>  	if (syscall_trace_enter(regs)) {
>>>  		result =3D -ENOSYS;
>>>  		goto out;
>>>  	}
>>> =20
>>> -	syscall =3D get_syscall(r);
>>> +	/* Get the syscall after being potentially updated with ptrace. *=
/
>>> +	syscall =3D UPT_SYSCALL_NR(r);
>>
>> Doesn't this break the support for changing syscall numbers using PT=
RACE_SETREGS?
>=20
> The logic is unchanged except updating the UPT_SYSCALL_NR before sysc=
all_trace_enter(). I did my last tests with the x86_32 subarchitecture =
and all tests (from selftest/seccomp), including PTRACE_SETREGS for sys=
call numbers tests, passed. However, 2 of this tests still fail for x86=
_64 (only).

No, you chagned the logic.
syscall_trace_enter() enters the ptrace() path, and here EAX/RAX can be=
 changed.
Hence, "syscall =3D UPT_SYSCALL_NR(r)" will still see the old syscall n=
umber.
--> changing syscall numbers got broken by you. :-)

Thanks,
//richard
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