[xen master] xen/common: Add NUMA node id bounds check to page_alloc.c/node_to_scrub

[patchbot@xxxxxxx]

commit a363089e68ed677fef12c296253535753fe817e3
Author:     Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Tue Sep 26 17:37:39 2023 -0500
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Wed Sep 27 16:28:55 2023 -0700

    xen/common: Add NUMA node id bounds check to page_alloc.c/node_to_scrub
    
    When building for Power with CONFIG_DEBUG unset, a compiler error gets
    raised inside page_alloc.c's node_to_scrub function:
    
    common/page_alloc.c: In function 'node_to_scrub.part.0':
    common/page_alloc.c:1217:29: error: array subscript 1 is above array
                bounds of 'long unsigned int[1]' [-Werror=array-bounds]
     1217 |         if ( node_need_scrub[node] )
    
    It appears that this is a false positive, given that in practice
    cycle_node should never return a node ID >= MAX_NUMNODES as long as the
    architecture's node_online_map is properly defined and initialized, so
    this additional bounds check is only to satisfy GCC.
    
    Signed-off-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/common/page_alloc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 35d9a26fa6..9b5df74fdd 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1211,6 +1211,14 @@ static unsigned int node_to_scrub(bool get_node)
         } while ( !cpumask_empty(&node_to_cpumask(node)) &&
                   (node != local_node) );
 
+        /*
+         * In practice `node` will always be within MAX_NUMNODES, but GCC can't
+         * always see that, so an explicit check is necessary to avoid tripping
+         * its out-of-bounds array access warning (-Warray-bounds).
+         */
+        if ( node >= MAX_NUMNODES )
+            break;
+
         if ( node == local_node )
             break;
 
--
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