Re: [dpdk-dev v2 1/2] eal: Add rte_consttime_memsq() to prevent timing attacks memcmp.

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Sep 26, 2025 at 11:07:52AM -0700, Stephen Hemminger wrote:
> On Fri, 26 Sep 2025 15:49:04 +0000
> Kai Ji <kai.ji@intel.com> wrote:
> 
> > Bugzilla ID: 1773
> > Cc: stable@dpdk.org
> > 
> > [0] https://bugs.dpdk.org/show_bug.cgi?id=1773
> > 
> > Signed-off-by: Kai Ji <kai.ji@intel.com>
> > ---
> >  lib/eal/include/rte_common.h | 34 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> > 
> > diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
> > index 9e7d84f929..ddbba083be 100644
> > --- a/lib/eal/include/rte_common.h
> > +++ b/lib/eal/include/rte_common.h
> > @@ -700,6 +700,40 @@ rte_is_aligned(const void * const __rte_restrict ptr, const unsigned int align)
> >  	return ((uintptr_t)ptr & (align - 1)) == 0;
> >  }
> >  
> > +/**
> > + * Constant-time memory inequality comparison.
> > + *
> > + * This function compares two memory regions in constant time, making it
> > + * resistant to timing side-channel attacks. The execution time depends only
> > + * on the length parameter, not on the actual data values being compared.
> > + *
> > + * This is particularly important for cryptographic operations where timing
> > + * differences could leak information about secret keys, passwords, or other
> > + * sensitive data.
> > + *
> > + * @param a
> > + *   Pointer to the first memory region to compare
> > + * @param b
> > + *   Pointer to the second memory region to compare
> > + * @param n
> > + *   Number of bytes to compare
> > + * @return
> > + *   false if the memory regions are identical, true if they differ
> > + */
> > +static inline bool
> > +rte_consttime_memneq(const void *a, const void *b, size_t n)
> > +{
> > +	const volatile uint8_t *pa = (const volatile uint8_t *)a;
> > +	const volatile uint8_t *pb = (const volatile uint8_t *)b;
> > +	uint8_t result = 0;
> > +	size_t i;
> > +
> > +	for (i = 0; i < n; i++)
> > +		result |= pa[i] ^ pb[i];
> > +
> > +	return result != 0;
> > +}
> 
> New functions usually have to be marked experimental.
> 
> Since DPDK adopts many things from FreeBSD, perhaps the function
> should use the same naming conventions. That would mean
> 
> int rte_consttime_memequal(void *, void *, size_t len);
> 
> And will also need to update release notes.

+1 for removing the "not" from the name which avoids having double
negatives in conditionals. Also agree with keeping consistency with BSD
name.

/Bruce