Re: [PATCH] rte_memcpy: fix off by one for size 16 and 32

[Mattias Rönnblom]

On 2024-03-02 21:49, Stephen Hemminger wrote:

The rte_memcpy code would do extra instructions for size 16
and 32 which potentially could reference past end of data.

For size of 16, only single mov16 is needed.
same for size of 32, only single mov32.

Fixes: f5472703c0bd ("eal: optimize aligned memcpy on x86")
Fixes: d35cc1fe6a7a ("eal/x86: revert select optimized memcpy at run-time")

Suggested-by: Morten Brørup <m...@smartsharesystems.com>
Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
---
  lib/eal/x86/include/rte_memcpy.h | 6 ++++--
  1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/eal/x86/include/rte_memcpy.h b/lib/eal/x86/include/rte_memcpy.h
index 72a92290e05d..00479a4bfbe6 100644
--- a/lib/eal/x86/include/rte_memcpy.h
+++ b/lib/eal/x86/include/rte_memcpy.h
@@ -233,13 +233,15 @@ rte_memcpy_generic(void *dst, const void *src, size_t n)
         */
        if (n <= 32) {
                rte_mov16((uint8_t *)dst, (const uint8_t *)src);
-               rte_mov16((uint8_t *)dst - 16 + n,
+               if (n > 16)
+                       rte_mov16((uint8_t *)dst - 16 + n,
                                  (const uint8_t *)src - 16 + n);
                return ret;
        }
        if (n <= 64) {
                rte_mov32((uint8_t *)dst, (const uint8_t *)src);
-               rte_mov32((uint8_t *)dst - 32 + n,
+               if (n > 32)

n is always > 32 here.

+                       rte_mov32((uint8_t *)dst - 32 + n,
                                  (const uint8_t *)src - 32 + n);
                return ret;
        }