Re: [PATCH 4/7] x86/entry: Increase entry_stack size to a full page

From: Marco Elver <elver@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	mhelsley@vmware.com, Steven Rostedt <rostedt@goodmis.org>,
	jthierry@redhat.com, mbenes@suse.cz,
	Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH 4/7] x86/entry: Increase entry_stack size to a full page
Date: Thu, 18 Jun 2020 17:06:00 +0200	[thread overview]
Message-ID: <CANpmjNNpnW2AyzKOQ8tuXvhs04Kugjuj0y+j4wMxA7YfDyOwxg@mail.gmail.com> (raw)
In-Reply-To: <20200618144801.819246178@infradead.org>

On Thu, 18 Jun 2020 at 16:50, Peter Zijlstra <peterz@infradead.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@amacapital.net>
> Reported-by: Marco Elver <elver@google.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

This fixes the unpredictable crashes.

Tested-by: Marco Elver <elver@google.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 {
>
>