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Date: Tue, 15 Aug 2017 09:09:36 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Mark Rutland <mark.rutland@....com>
Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Catalin Marinas <catalin.marinas@....com>,
James Morse <james.morse@....com>, Laura Abbott <labbott@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Matt Fleming <matt@...eblueprint.co.uk>,
Will Deacon <will.deacon@....com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCHv2 02/14] fork: allow arch-override of VMAP stack alignment
On Tue, Aug 15, 2017 at 5:50 AM, Mark Rutland <mark.rutland@....com> wrote:
> In some cases, an architecture might wish its stacks to be aligned to a
> boundary larger than THREAD_SIZE. For example, using an alignment of
> double THREAD_SIZE can allow for stack overflows smaller than
> THREAD_SIZE to be detected by checking a single bit of the stack
> pointer.
>
> This patch allows architectures to override the alignment of VMAP'd
> stacks, by defining THREAD_ALIGN. Where not defined, this defaults to
> THREAD_SIZE, as is the case today.
This looks okay, but it might make sense to move that to a header file
so THREAD_ALIGN is always available.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: linux-kernel@...r.kernel.org
> ---
> kernel/fork.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 17921b0..696d692 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -217,7 +217,10 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
> return s->addr;
> }
>
> - stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE,
> +#ifndef THREAD_ALIGN
> +#define THREAD_ALIGN THREAD_SIZE
> +#endif
> + stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
> VMALLOC_START, VMALLOC_END,
> THREADINFO_GFP,
> PAGE_KERNEL,
> --
> 1.9.1
>
--
Andy Lutomirski
AMA Capital Management, LLC
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