Date: Sat, 19 May 2018 00:12:49 +0300 From: Alexander Popov <alex.popov@...ux.com> To: Ingo Molnar <mingo@...nel.org> Cc: kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>, PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>, Andy Lutomirski <luto@...nel.org>, Tycho Andersen <tycho@...ho.ws>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Borislav Petkov <bp@...en8.de>, Richard Sandiford <richard.sandiford@....com>, 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>, Jonathan Corbet <corbet@....net>, Andrey Ryabinin <aryabinin@...tuozzo.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Thomas Garnier <thgarnie@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Alexei Starovoitov <ast@...nel.org>, Josef Bacik <jbacik@...com>, Masami Hiramatsu <mhiramat@...nel.org>, Nicholas Piggin <npiggin@...il.com>, Al Viro <viro@...iv.linux.org.uk>, "David S . Miller" <davem@...emloft.net>, Ding Tianhong <dingtianhong@...wei.com>, David Woodhouse <dwmw@...zon.co.uk>, Josh Poimboeuf <jpoimboe@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Dominik Brodowski <linux@...inikbrodowski.net>, Juergen Gross <jgross@...e.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Dan Williams <dan.j.williams@...el.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Mathias Krause <minipli@...glemail.com>, Vikas Shivappa <vikas.shivappa@...ux.intel.com>, Kyle Huey <me@...ehuey.com>, Dmitry Safonov <dsafonov@...tuozzo.com>, Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>, Florian Weimer <fweimer@...hat.com>, 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 Hello Ingo, Thanks a lot for the review! I agree with your points. I'll fix the series and return with v13. There are some comments/questions below. On 18.05.2018 09:53, Ingo Molnar wrote: > * Alexander Popov <alex.popov@...ux.com> wrote: >> + /* >> + * It would be nice not to have p and boundary on the stack. >> + * Setting the register specifier for them is the best we can do. >> + */ >> + register unsigned long p = current->thread.lowest_stack.val; >> + register unsigned long boundary = p & ~(THREAD_SIZE - 1); > > Does the 'register' keyword actually have any effect on the generated code? No, for gcc it doesn't give any effect for this code. I used it to show the intention. However, even if the compiler allocates 'p' and 'boundary' on stack, that will not break the stack erasing. Should I drop 'register'? >> + unsigned long poison = 0; >> + const unsigned long check_depth = STACKLEAK_POISON_CHECK_DEPTH / >> + sizeof(unsigned long); > > Please don't break lines in such an ugly fashion! Ok. I'll make it look like that: const unsigned long check_depth = STACKLEAK_POISON_CHECK_DEPTH / sizeof(unsigned long); > Also, 'poison' is a very weird name for something that looks like an index. > > Plus since it's bound by "check_depth" is the 'unsigned long' justified, > or could it be 32-bit? Thanks, I can turn both 'check_depth' and 'poison' (which I'll rename) into 'unsigned int'. >> + /* Reset the lowest_stack value for the next syscall */ >> + current->thread.lowest_stack.val = current_top_of_stack() - 256; > > Magic, unexplained '256' literal. Here I'm choosing the point from which we'll start the poison search on the next syscall in case 'lowest_stack' is not updated in track_stack(). Would you like if I use "current_top_of_stack() - THREAD_SIZE / 64" ? Best regards, Alexander
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