kernel-hardening - Re: [PATCH RFC v4 1/3] gcc-plugins: Add STACKLEAK erasing the kernel stack at the end of syscalls

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Message-ID: <ac934200-74e0-3e0d-fd14-dff64197c03a@linux.com>
Date: Fri, 13 Oct 2017 20:03:59 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: kernel-hardening@...ts.openwall.com, keescook@...omium.org,
 pageexec@...email.hu, spender@...ecurity.net, tycho@...ker.com,
 Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>,
 Ard Biesheuvel <ard.biesheuvel@...aro.org>,
 Andy Lutomirski <luto@...capital.net>, x86@...nel.org,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>,
 Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH RFC v4 1/3] gcc-plugins: Add STACKLEAK erasing the kernel
 stack at the end of syscalls

Hello Ingo,

On 05.10.2017 10:27, Ingo Molnar wrote:
> - The GCC plugin adds instrumentation in form of extra 'track_stack()' and
>   'check_alloca()' calls. Could you please provide a frequency analysis of the
>   impact of this: x86-64 defconfig vmlinux size before/after the patch, and the
>   number of instrumentation function calls inserted, compared to the number of
>   functions?

Size of vmlinux (x86_64_defconfig):
 file size:
  - STACKLEAK disabled: 35014784 bytes
  - STACKLEAK enabled: 35044952 bytes (+0.086%)
 .text section size (calculated by size utility):
  - STACKLEAK disabled: 10752983
  - STACKLEAK enabled: 11062221 (+2.876%)

The readelf utility shows 45602 functions in vmlinux.

The STACKLEAK gcc plugin inserted 36 check_alloca() calls and 1265 track_stack()
calls (42274 calls are inserted during GIMPLE pass and 41009 calls are deleted
during RTL pass). So 2.853% of functions are instrumented.

I will add this information to the cover letter of the 5'th version, which I'm
currently preparing.

Best regards,
Alexander

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