Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 7 Aug 2017 14:44:22 -0700
From: Kees Cook <>
To: Ard Biesheuvel <>
Cc: "" <>, Mark Rutland <>, 
	Catalin Marinas <>, James Morse <>, 
	Laura Abbott <>, Andy Lutomirski <>, 
	Matt Fleming <>, Will Deacon <>, 
	Kernel Hardening <>, 
	"" <>
Subject: Re: [PATCH] lkdtm: Test VMAP_STACK allocates
 leading/trailing guard pages

On Mon, Aug 7, 2017 at 2:27 PM, Ard Biesheuvel
<> wrote:
> On 7 August 2017 at 21:39, Kees Cook <> wrote:
>> attempt to read the byte before and after, respectively, of the current
>> stack frame, which should fault under VMAP_STACK.
>> Signed-off-by: Kees Cook <>
>> ---
>> Do these tests both trip with the new arm64 VMAP_STACK code?
> Probably not. On arm64, the registers are stacked by software at
> exception entry,  and so we decrement the sp first by the size of the
> register file, and if the resulting value overflows the stack, the
> situation is handled as if the exception was caused by a faulting
> stack access while it may be caused by something else in reality.
> Since the act of handling the exception is guaranteed to overflow the
> stack anyway, this does not really make a huge difference, and it
> prevents the recursive fault from wiping the context that we need to
> produce the diagnostics.
> This means an illegal access right above the stack will go undetected.

I thought vmap entries provided guard pages around allocations?
Shouldn't that catch it?

Kees Cook
Pixel Security

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.