[v2,1/2] gnttab: almost fully ignore zero-size flush requests

Commit Message

Jan Beulich Feb. 26, 2024, 10:44 a.m. UTC

Along the line with observations in the context of XSA-448, besides
"op" no field is relevant when the range to be flushed is empty, much
like e.g. the pointers passed to memcpy() are irrelevant (and would
never be "validated") when the passed length is zero. Split the existing
condition validating "op", "offset", and "length", leaving only the "op"
part ahead of the check for length being zero (or no flushing to be
performed).

Signed-off-by: Jan Beulich <[e-mail]>
---
v2: Undo expression folding.

Patch

--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -3528,15 +3528,17 @@  static int _cache_flush(const gnttab_cac
     void *v;
     int ret;
 
-    if ( (cflush->offset >= PAGE_SIZE) ||
-         (cflush->length > PAGE_SIZE) ||
-         (cflush->offset + cflush->length > PAGE_SIZE) ||
-         (cflush->op & ~(GNTTAB_CACHE_INVAL | GNTTAB_CACHE_CLEAN)) )
+    if ( cflush->op & ~(GNTTAB_CACHE_INVAL | GNTTAB_CACHE_CLEAN) )
         return -EINVAL;
 
     if ( cflush->length == 0 || cflush->op == 0 )
         return !*cur_ref ? 0 : -EILSEQ;
 
+    if ( (cflush->offset >= PAGE_SIZE) ||
+         (cflush->length > PAGE_SIZE) ||
+         cflush->offset + cflush->length > PAGE_SIZE )
+        return -EINVAL;
+
     /* currently unimplemented */
     if ( cflush->op & GNTTAB_CACHE_SOURCE_GREF )
         return -EOPNOTSUPP;