[Xen-changelog] [xen staging] x86/HVM: don't crash guest in hvmemul_find_mmio_cache()

[patchbot@xxxxxxx]

commit a43c1dec246bdee484e6a3de001cc6850a107abe
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Mar 12 14:39:46 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Mar 12 14:39:46 2019 +0100

    x86/HVM: don't crash guest in hvmemul_find_mmio_cache()
    
    Commit 35a61c05ea ("x86emul: adjust handling of AVX2 gathers") builds
    upon the fact that the domain will actually survive running out of MMIO
    result buffer space. Drop the domain_crash() invocation. Also delay
    incrementing of the usage counter, such that the function can't possibly
    use/return an out-of-bounds slot/pointer in case execution subsequently
    makes it into the function again without a prior reset of state.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 xen/arch/x86/hvm/emulate.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 2d02ef1521..754baf68d5 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -966,12 +966,11 @@ static struct hvm_mmio_cache *hvmemul_find_mmio_cache(
             return cache;
     }
 
-    i = vio->mmio_cache_count++;
+    i = vio->mmio_cache_count;
     if( i == ARRAY_SIZE(vio->mmio_cache) )
-    {
-        domain_crash(current->domain);
         return NULL;
-    }
+
+    ++vio->mmio_cache_count;
 
     cache = &vio->mmio_cache[i];
     memset(cache, 0, sizeof (*cache));
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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