[Xen-changelog] [xen staging] xen/vcpu: Improve sanity checks in vcpu_create()

[patchbot@xxxxxxx]

commit b6d41060120562e2185f2e3b5e582d415456ec65
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Jan 15 18:44:18 2020 +0000
Commit:     Julien Grall <julien@xxxxxxx>
CommitDate: Thu Jan 16 12:44:57 2020 +0000

    xen/vcpu: Improve sanity checks in vcpu_create()
    
    The BUG_ON() is confusing to follow.  The (!is_idle_domain(d) || vcpu_id) 
part
    is a vestigial remnant of architectures poisioning idle_vcpu[0] with 
non-NULL
    pointers.
    
    Now that idle_vcpu[0] is NULL on all architectures, and d->max_vcpus 
specified
    before vcpu_create() is called, we can properly range check the requested
    vcpu_id.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Julien Grall <julien@xxxxxxx>
---
 xen/common/domain.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 0b1103fdb2..ee3f9ffd3e 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -139,7 +139,19 @@ struct vcpu *vcpu_create(struct domain *d, unsigned int 
vcpu_id)
 {
     struct vcpu *v;
 
-    BUG_ON((!is_idle_domain(d) || vcpu_id) && d->vcpu[vcpu_id]);
+    /*
+     * Sanity check some input expectations:
+     * - vcpu_id should be bounded by d->max_vcpus, and not previously
+     *   allocated.
+     * - VCPUs should be tightly packed and allocated in ascending order,
+     *   except for the idle domain which may vary based on PCPU numbering.
+     */
+    if ( vcpu_id >= d->max_vcpus || d->vcpu[vcpu_id] ||
+         (!is_idle_domain(d) && vcpu_id && !d->vcpu[vcpu_id - 1]) )
+    {
+        ASSERT_UNREACHABLE();
+        return NULL;
+    }
 
     if ( (v = alloc_vcpu_struct(d)) == NULL )
         return NULL;
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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