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Message-ID: <24c5699b-d222-486b-6f16-7539e931c436@linux.com>
Date: Thu, 24 May 2018 16:05:27 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>
Cc: kernel-hardening@...ts.openwall.com, PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>, Andy Lutomirski <luto@...nel.org>,
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Ard Biesheuvel <ard.biesheuvel@...aro.org>, Borislav Petkov <bp@...en8.de>,
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Thomas Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Dmitry V . Levin"
<ldv@...linux.org>, Emese Revfy <re.emese@...il.com>,
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<me@...ehuey.com>, Dmitry Safonov <dsafonov@...tuozzo.com>,
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Boris Lukashev <blukashev@...pervictus.com>,
Andrey Konovalov <andreyknvl@...gle.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 2/6] x86/entry: Add STACKLEAK erasing the kernel stack
at the end of syscalls
On 18.05.2018 09:53, Ingo Molnar wrote:
> * Alexander Popov <alex.popov@...ux.com> wrote:
>> + if (on_thread_stack())
>> + boundary = current_stack_pointer;
>> + else
>> + boundary = current_top_of_stack();
>> +
>> + BUG_ON(boundary - p >= THREAD_SIZE);
>
> Please make this:
>
> if ( WARN_ON_ONCE())
> return;
>
> ... or so, so that if this code is buggy we get actual useful user reports, not
> just "my machine froze, help!"...
I've just double-checked that BUG() in erase_kstack() works fine when it's
called from the trampoline stack and thread stack.
But this "WARN_ON_ONCE() + return" logic would introduce an undesirable effect:
modifying 'lowest_stack' value would allow to silently skip stack erasing.
Best regards,
Alexander
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