[xen master] xen: Check the alignment of the offset pased via VCPUOP_register_vcpu_info

[patchbot@xxxxxxx]

commit 3fdc211b01b29f252166937238efe02d15cb5780
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Tue May 26 18:31:33 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jul 7 14:41:00 2020 +0200

    xen: Check the alignment of the offset pased via VCPUOP_register_vcpu_info
    
    Currently a guest is able to register any guest physical address to use
    for the vcpu_info structure as long as the structure can fits in the
    rest of the frame.
    
    This means a guest can provide an address that is not aligned to the
    natural alignment of the structure.
    
    On Arm 32-bit, unaligned access are completely forbidden by the
    hypervisor. This will result to a data abort which is fatal.
    
    On Arm 64-bit, unaligned access are only forbidden when used for atomic
    access. As the structure contains fields (such as evtchn_pending_self)
    that are updated using atomic operations, any unaligned access will be
    fatal as well.
    
    While the misalignment is only fatal on Arm, a generic check is added
    as an x86 guest shouldn't sensibly pass an unaligned address (this
    would result to a split lock).
    
    This is XSA-327.
    
    Reported-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/common/domain.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 7cc9526139..e9be05f1d0 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1227,10 +1227,20 @@ int map_vcpu_info(struct vcpu *v, unsigned long gfn, 
unsigned offset)
     void *mapping;
     vcpu_info_t *new_info;
     struct page_info *page;
+    unsigned int align;
 
     if ( offset > (PAGE_SIZE - sizeof(vcpu_info_t)) )
         return -EINVAL;
 
+#ifdef CONFIG_COMPAT
+    if ( has_32bit_shinfo(d) )
+        align = alignof(new_info->compat);
+    else
+#endif
+        align = alignof(*new_info);
+    if ( offset & (align - 1) )
+        return -EINVAL;
+
     if ( !mfn_eq(v->vcpu_info_mfn, INVALID_MFN) )
         return -EINVAL;
 
--
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