Re: [PATCH 5/5] x86/asm/entry/32: Simplify ptrace register shuffling

From: Ingo Molnar <mingo@kernel.org>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Oleg Nesterov <oleg@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] x86/asm/entry/32: Simplify ptrace register shuffling
Date: Thu, 18 Jun 2015 11:33:15 +0200	[thread overview]
Message-ID: <20150618093315.GB1094@gmail.com> (raw)
In-Reply-To: <1433876051-26604-5-git-send-email-dvlasenk@redhat.com>

* Denys Vlasenko <dvlasenk@redhat.com> wrote:

> Before this patch, we were clearing pt_regs->r8..r11 on stack.
> We can as well just store actual r8..r11 registers there:
> they came from userspace, we leak no information by showing them to ptrace.
> This allows to get rid of one insn ("xor %eax,%eax").
> Not a big deal, but still...
> 
> After call to syscall_trace_enter(), before this patch we were restoring
> clobbered registers and jump to code which converts 32-bit syscall
> ABI to 64-bit C ABI. This is unnecessary work, we can combine both
> steps into one (similar to what audit code does already).

So this really needs a description about what kind of testing was done, as 
technically this changes the ABI. Heavy ptrace users should be tried: strace,
UML, etc.

I don't expect any problems, but still it needs to be tested.

Thanks,

	Ingo