linux-kernel - Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs

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Date:	Mon, 21 Dec 2015 11:13:33 +0100
From:	Richard Weinberger <richard@....at>
To:	Mickaël Salaün <mic@...ikod.net>,
	linux-kernel@...r.kernel.org
Cc:	Jonathan Corbet <corbet@....net>, Jeff Dike <jdike@...toit.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>,
	Shuah Khan <shuahkh@....samsung.com>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Hogan <james.hogan@...tec.com>,
	Thomas Meyer <thomas@...3r.de>,
	Nicolas Iooss <nicolas.iooss_linux@....org>,
	Anton Ivanov <aivanov@...cade.com>, linux-doc@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net,
	user-mode-linux-user@...ts.sourceforge.net,
	linux-api@...r.kernel.org,
	Meredydd Luff <meredydd@...atehouse.org>,
	David Drysdale <drysdale@...gle.com>
Subject: Re: [PATCH v1 1/4] um: Fix ptrace GETREGS/SETREGS bugs

Am 21.12.2015 um 10:23 schrieb Mickaël Salaün:
>>>> Doesn't this break the support for changing syscall numbers using PTRACE_SETREGS?
>>>
>>> The logic is unchanged except updating the UPT_SYSCALL_NR before syscall_trace_enter(). I did my last tests with the x86_32 subarchitecture and all tests (from selftest/seccomp), including PTRACE_SETREGS for syscall numbers tests, passed. However, 2 of this tests still fail for x86_64 (only).
>>
>> No, the logic is different.
>> syscall_trace_enter(regs) enters the ptrace() path and here registers can be changed.
>> Hence "syscall = UPT_SYSCALL_NR(r);" will see the old syscall number.
>> UPT_SYSCALL_NR() returns the syscall number before the ptrace() path...
> 
> The thing is, PTRACE_SETREGS give access to *orig_ax* in the user_regs_struct from arch/x86/include/asm/user_*.h and selftest/seccomp only update this (virtual) register, not the EAX/RAX. Am I missing something?

Sorry, meant orig...

Please see the attached program. It proves that your patch is breaking stuff.
The test is extracted from UML's selftests.

Thanks,
//richard

View attachment "ptsc.c" of type "text/x-csrc" (4642 bytes)