[Xen-devel] [PATCH] tools/libxc: Don't leave scratch_pfn uninitialised if the domain has no memory

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s 5b5c40c0d1 "libxc: introduce a per architecture scratch pfn for temporary
grant mapping" accidentally an issue whereby there were two paths out of
xc_core_arch_get_scratch_gpfn() which returned 0, but only one of which
assigned a value to the gpfn parameter.

xc_domain_maximum_gpfn() can validly return 0, at which point gpfn 1 is a
valid scratch page to use.

In addition, widen rc before adding 1 and possibly overflowing.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxc/xc_core_x86.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/libxc/xc_core_x86.c b/tools/libxc/xc_core_x86.c
index fac99ec..d8846f1 100644
--- a/tools/libxc/xc_core_x86.c
+++ b/tools/libxc/xc_core_x86.c
@@ -214,10 +214,10 @@ xc_core_arch_get_scratch_gpfn(xc_interface *xch, domid_t 
domid,
 
     rc = xc_domain_maximum_gpfn(xch, domid);
 
-    if ( rc <= 0 )
+    if ( rc < 0 )
         return rc;
 
-    *gpfn = rc + 1;
+    *gpfn = (xen_pfn_t)rc + 1;
 
     return 0;
 }
-- 
1.7.10.4


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