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

[Morten Brørup]

> From: Kai Ji [mailto:kai.ji at 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 at 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.

-Morten