linux-kernel - Re: [PATCH] x86/sgx: Avoid returning NULL in __sgx_alloc_epc

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Date:   Fri, 19 Mar 2021 16:52:49 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Kai Huang <kai.huang@...el.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, dave.hansen@...ux.intel.com,
        dave.hansen@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: Avoid returning NULL in __sgx_alloc_epc_page()

On Fri, Mar 19, 2021 at 05:22:56PM +0200, Jarkko Sakkinen wrote:
> I did misread it for the first time.
> 
> So let's sanity: you *are* going to squash the patches together because
> that way it's factors easier to backport the whole thing?
> 
> Is this the correct understanding?

I squashed Kai's fix because I don't want to break people's bisection if
they land between your patch and his fix. They're already troubled enough
chasing an issue, don't want to have them get a NULL ptr in sgx land.

Now, looking at dhansen's fix: what can happen if nid is uninitialized?
AFAICT, we'll end up in

static inline int __next_node(int n, const nodemask_t *srcp)
{
        return min_t(int,MAX_NUMNODES,find_next_bit(srcp->bits, MAX_NUMNODES, n+1));
}

with n uninitialized and depending on its value it'll either return
MAX_NUMNODES so we'll try to allocate on the first node or try to
allocate on some other node.

Now, if you think that that is still problematic enough for enclave
creation, then I'll fold his patch too.

So yes, the main reason is usability and not breaking bisection.

So, what would you prefer?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette