Re: [Xen-devel] [PATCH] xen/vcpu: Improve sanity checks in vcpu_create()

[Julien Grall]

Hi,

On 16/01/2020 09:55, Jan Beulich wrote:

On 15.01.2020 19:44, Andrew Cooper wrote:

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.


I guess this is meant to be true on top of your Arm side change
which hasn't been committed yet? And perhaps better "... starts
out as NULL on all ..."?


I can commit the two together.




Signed-off-by: Andrew Cooper 


Reviewed-by: Jan Beulich 


Acked-by: Julien Grall 

Cheers,

--
Julien Grall

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Re: [Xen-devel] [PATCH] xen/vcpu: Improve sanity checks in vcpu_create()

[Jan Beulich]

On 15.01.2020 19:44, Andrew Cooper wrote:
> 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.

I guess this is meant to be true on top of your Arm side change
which hasn't been committed yet? And perhaps better "... starts
out as NULL on all ..."?

> Signed-off-by: Andrew Cooper 

Reviewed-by: Jan Beulich 

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[Xen-devel] [PATCH] xen/vcpu: Improve sanity checks in vcpu_create()

[Andrew Cooper]

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 
---
CC: Jan Beulich 
CC: Wei Liu 
CC: Roger Pau Monné 
CC: Stefano Stabellini 
CC: Julien Grall 
CC: Volodymyr Babchuk 
---
 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;
-- 
2.11.0


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