Re: [dpdk-dev v3 1/2] eal: Add rte_consttime_memneq() to prevent timing attacks memcmp.

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 26 Sep 2025 21:17:08 +0200
Morten Brørup <mb@smartsharesystems.com> wrote:

> > From: Kai Ji [mailto:kai.ji@intel.com]
> > Sent: Friday, 26 September 2025 18.02
> > 
> > Bugzilla ID: 1773
> > 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;
> > +}
> > +
> >  /*********** Macros for compile type checks ********/
> > 
> >  /* Workaround for toolchain issues with missing C11 macro in FreeBSD
> > */
> > --
> > 2.34.1  
> 
> My comments here still apply:
> https://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35F6547A@smartserver.smartshare.dk/
> 
> Also, this is certainly not a common function, so don't put it in rte_commo.h. Put it in rte_memory.h as suggested.

Yes, Should be next to existing rte_memzero_explicit in rte_memory.h