linux-hardening - Re: [PATCH] powerpc/pseries: Whitelist dtl slub object for copying to userspace

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Message-ID: <87zfrecypq.fsf@mail.lhotse>
Date: Fri, 21 Jun 2024 21:38:41 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Anjali K <anjalik@...ux.ibm.com>, Kees Cook <kees@...nel.org>
Cc: linuxppc-dev@...ts.ozlabs.org, npiggin@...il.com, naveen@...nel.org,
 christophe.leroy@...roup.eu, gustavoars@...nel.org,
 linux-hardening@...r.kernel.org, vishalc@...ux.ibm.com
Subject: Re: [PATCH] powerpc/pseries: Whitelist dtl slub object for copying
 to userspace

Anjali K <anjalik@...ux.ibm.com> writes:
> Hi Michael
>
> On 18/06/24 12:41, Michael Ellerman wrote:
>> I guess there isn't a kmem_cache_create_user_readonly() ?

> Thank you for your review.                                                    
> 
> My understanding of the question is whether there's a way to whitelist a   
> region such that it can be copied to userspace, but not written to using   
> copy_from_user().                                                             
 
Yes that's what I meant, and I pretty much worked that out from looking
at the implementation, but was hoping Kees would tell me it was there
somewhere, or implement it :)  Apologies for being cryptic.

> No, we don't have a function to whitelist only for copy_to_user() and not  
> copy_from_user().

Yep. I'll take this patch as-is, I think we've established that it's
pretty low risk to whitelist the whole cache.

cheers