[Xen-devel] [PATCH 2/2] xen/balloon: Fix crash when ballooning on x86 32 bit PAE

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

When ballooning on an x86 32 bit PAE system with close to 64 GiB of memory, the
address returned by allocate_resource may be above 64 GiB.  When using
CONFIG_SPARSEMEM, this setup is limited to using physical addresses < 64 GiB.
When adding memory at this address, it runs off the end of the mem_section
array and causes a crash.  Instead, fail the ballooning request.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 drivers/xen/balloon.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 12eab50..329695d 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -152,6 +152,8 @@ static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
 static void balloon_process(struct work_struct *work);
 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
 
+static void release_memory_resource(struct resource *resource);
+
 /* When ballooning out (allocating memory to return to Xen) we don't really
    want the kernel to try too hard since that can trigger the oom killer. */
 #define GFP_BALLOON \
@@ -268,6 +270,19 @@ static struct resource 
*additional_memory_resource(phys_addr_t size)
                return NULL;
        }
 
+#ifdef CONFIG_SPARSEMEM
+       {
+               unsigned long max_pfn = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
+               unsigned long pfn = res->start >> PAGE_SHIFT;
+
+               if (pfn > max_pfn) {
+                       pr_err("pfn %lu exceeds max_pfn %lu\n", pfn, max_pfn);
+                       release_memory_resource(res);
+                       return NULL;
+               }
+       }
+#endif
+
        return res;
 }
 
-- 
2.4.3


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