[PATCH v2 02/16] x86/mm/numa: Remove uninitialized_var() usage

Kees Cook
2020-06-20T03:33:45Z

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings (e.g.
"unused variable"). If the compiler thinks it is uninitialized, either
simply initialize the variable or make compiler changes. As a precursor
to removing[2] this[3] macro[4], refactor code to avoid its need.

The original reason for its use here was to work around the #ifdef
being the only place the variable was used. This is better expressed
using IS_ENABLED() and a new code block where the variable can be used
unconditionally.

[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Fixes: 1e01979c8f50 ("x86, numa: Implement pfn -> nid mapping granularity check")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/x86/mm/numa.c | 18 +++++++++---------
include/linux/page-flags-layout.h | 4 +++-
2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index 8ee952038c80..b05f45e5e8e2 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -543,7 +543,6 @@ static void __init numa_clear_kernel_node_hotplug(void)

static int __init numa_register_memblks(struct numa_meminfo *mi)
{
- unsigned long uninitialized_var(pfn_align);
int i, nid;

/* Account for nodes with cpus and no memory */
@@ -571,15 +570,16 @@ static int __init numa_register_memblks(struct numa_meminfo *mi)
* If sections array is gonna be used for pfn -> nid mapping, check
* whether its granularity is fine enough.
*/
-#ifdef NODE_NOT_IN_PAGE_FLAGS
- pfn_align = node_map_pfn_alignment();
- if (pfn_align && pfn_align < PAGES_PER_SECTION) {
- printk(KERN_WARNING "Node alignment %LuMB < min %LuMB, rejecting NUMA config\n",
- PFN_PHYS(pfn_align) >> 20,
- PFN_PHYS(PAGES_PER_SECTION) >> 20);
- return -EINVAL;
+ if (IS_ENABLED(NODE_NOT_IN_PAGE_FLAGS)) {
+ unsigned long pfn_align = node_map_pfn_alignment();
+
+ if (pfn_align && pfn_align < PAGES_PER_SECTION) {
+ pr_warn("Node alignment %LuMB < min %LuMB, rejecting NUMA config\n",
+ PFN_PHYS(pfn_align) >> 20,
+ PFN_PHYS(PAGES_PER_SECTION) >> 20);
+ return -EINVAL;
+ }
}
-#endif
if (!numa_meminfo_cover_memory(mi))
return -EINVAL;

diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
index 71283739ffd2..e200eef6a7fd 100644
--- a/include/linux/page-flags-layout.h
+++ b/include/linux/page-flags-layout.h
@@ -98,9 +98,11 @@
/*
* We are going to use the flags for the page to node mapping if its in
* there. This includes the case where there is no node, so it is implicit.
+ * Note that this #define MUST have a value so that it can be tested with
+ * the IS_ENABLED() macro.
*/
#if !(NODES_WIDTH > 0 || NODES_SHIFT == 0)
-#define NODE_NOT_IN_PAGE_FLAGS
+#define NODE_NOT_IN_PAGE_FLAGS 1
#endif

#if defined(CONFIG_NUMA_BALANCING) && LAST_CPUPID_WIDTH == 0
--
2.25.1