linux-kernel - Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree

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Message-ID: <5c70746c-ecfc-316f-f1ff-ab432cf9f32d@redhat.com>
Date:   Tue, 16 Jun 2020 15:43:16 -0400
From:   Waiman Long <longman@...hat.com>
To:     Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        David Sterba <dsterba@...e.cz>,
        "Jason A . Donenfeld" <Jason@...c4.com>, linux-mm@...ck.org,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-amlogic@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-ppp@...r.kernel.org, wireguard@...ts.zx2c4.com,
        linux-wireless@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, ecryptfs@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-bluetooth@...r.kernel.org,
        linux-wpan@...r.kernel.org, linux-sctp@...r.kernel.org,
        linux-nfs@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org
Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()

On 6/16/20 2:53 PM, Joe Perches wrote:
> On Mon, 2020-06-15 at 21:57 -0400, Waiman Long wrote:
>>   v4:
>>    - Break out the memzero_explicit() change as suggested by Dan Carpenter
>>      so that it can be backported to stable.
>>    - Drop the "crypto: Remove unnecessary memzero_explicit()" patch for
>>      now as there can be a bit more discussion on what is best. It will be
>>      introduced as a separate patch later on after this one is merged.
> To this larger audience and last week without reply:
> https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/
>
> Are there _any_ fastpath uses of kfree or vfree?

I am not sure about that, but both of them can be slow.


>
> Many patches have been posted recently to fix mispairings
> of specific types of alloc and free functions.
>
> To eliminate these mispairings at a runtime cost of four
> comparisons, should the kfree/vfree/kvfree/kfree_const
> functions be consolidated into a single kfree?
>
> Something like the below:
>
>     void kfree(const void *addr)
>     {
>     	if (is_kernel_rodata((unsigned long)addr))
>     		return;
>
>     	if (is_vmalloc_addr(addr))
>     		_vfree(addr);
>     	else
>     		_kfree(addr);
>     }
>
is_kernel_rodata() is inlined, but is_vmalloc_addr() isn't. So the 
overhead can be a bit bigger.

Cheers,
Longman