Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()

Waiman Long
2020-06-16T20:01:46Z

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?
>
> 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);
> }
>
> #define kvfree kfree
> #define vfree kfree
> #define kfree_const kfree
>
>
How about adding CONFIG_DEBUG_VM code to check for invalid address
ranges in kfree() and vfree()? By doing this, we can catch unmatched
pairing in debug mode, but won't have the overhead when debug mode is off.

Thought?

Cheers,
Longman