linux-kernel - Re: [PATCH 4/7] x86/entry: Increase entry

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Date:   Thu, 18 Jun 2020 17:06:00 +0200
From:   Marco Elver <elver@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Mark Rutland <mark.rutland@....com>, mhelsley@...are.com,
        Steven Rostedt <rostedt@...dmis.org>, jthierry@...hat.com,
        mbenes@...e.cz, Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH 4/7] x86/entry: Increase entry_stack size to a full page

On Thu, 18 Jun 2020 at 16:50, Peter Zijlstra <peterz@...radead.org> wrote:
>
> Marco crashed in bad_iret with a Clang11/KCSAN build due to
> overflowing the stack. Now that we run C code on it, expand it to a
> full page.
>
> Suggested-by: Andy Lutomirski <luto@...capital.net>
> Reported-by: Marco Elver <elver@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

This fixes the unpredictable crashes.

Tested-by: Marco Elver <elver@...gle.com>

Thanks!


> ---
>  arch/x86/include/asm/processor.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -370,7 +370,7 @@ struct x86_hw_tss {
>  #define IO_BITMAP_OFFSET_INVALID       (__KERNEL_TSS_LIMIT + 1)
>
>  struct entry_stack {
> -       unsigned long           words[64];
> +       char    stack[PAGE_SIZE];
>  };
>
>  struct entry_stack_page {
>
>