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Subject: Re: [PATCH RFC v10 2/6] x86/entry: Add STACKLEAK erasing the kernel
 stack at the end of syscalls
To: Alexander Popov <alex.popov@linux.com>,
 kernel-hardening@lists.openwall.com, Kees Cook <keescook@chromium.org>,
 PaX Team <pageexec@freemail.hu>, Brad Spengler <spender@grsecurity.net>,
 Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>,
 Tycho Andersen <tycho@tycho.ws>, Laura Abbott <labbott@redhat.com>,
 Mark Rutland <mark.rutland@arm.com>,
 Ard Biesheuvel <ard.biesheuvel@linaro.org>, Borislav Petkov <bp@alien8.de>,
 Richard Sandiford <richard.sandiford@arm.com>,
 Thomas Gleixner <tglx@linutronix.de>, "H . Peter Anvin" <hpa@zytor.com>,
 Peter Zijlstra <a.p.zijlstra@chello.nl>, "Dmitry V . Levin"
 <ldv@altlinux.org>, Emese Revfy <re.emese@gmail.com>,
 Jonathan Corbet <corbet@lwn.net>, Andrey Ryabinin <aryabinin@virtuozzo.com>,
 "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
 Thomas Garnier <thgarnie@google.com>,
 Andrew Morton <akpm@linux-foundation.org>,
 Alexei Starovoitov <ast@kernel.org>, Josef Bacik <jbacik@fb.com>,
 Masami Hiramatsu <mhiramat@kernel.org>, Nicholas Piggin <npiggin@gmail.com>,
 Al Viro <viro@zeniv.linux.org.uk>, "David S . Miller" <davem@davemloft.net>,
 Ding Tianhong <dingtianhong@huawei.com>, David Woodhouse
 <dwmw@amazon.co.uk>, Josh Poimboeuf <jpoimboe@redhat.com>,
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 Juergen Gross <jgross@suse.com>,
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 Vikas Shivappa <vikas.shivappa@linux.intel.com>, Kyle Huey
 <me@kylehuey.com>, Dmitry Safonov <dsafonov@virtuozzo.com>,
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References: <1522267032-6603-1-git-send-email-alex.popov@linux.com>
 <1522267032-6603-3-git-send-email-alex.popov@linux.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <77fab6ea-0bbf-d68b-a38e-3e22d1ae6093@linux.intel.com>
Date: Wed, 28 Mar 2018 15:55:24 -0700
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On 03/28/2018 12:57 PM, Alexander Popov wrote:
> +.macro ERASE_KSTACK
> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
> +	PUSH_AND_CLEAR_REGS
> +	call erase_kstack
> +	POP_REGS
> +#endif
> +.endm

Thanks again for the hard work to trim down the complexity of the
assembly.  I noticed the 64-bit version saves/restores registers while
the 32-bit version doesn't.  What's the reasoning there?