[xen stable-4.18] tools/dombuilder: Correct the length calculation in xc_dom_alloc_segment()

[patchbot@xxxxxxx]

commit 8e51c8f1d45fad242a315fa17ba3582c02e66840
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jul 4 14:12:31 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 4 14:12:31 2024 +0200

    tools/dombuilder: Correct the length calculation in xc_dom_alloc_segment()
    
    xc_dom_alloc_segment() is passed a size in bytes, calculates a size in pages
    from it, then fills in the new segment information with a bytes value
    re-calculated from the number of pages.
    
    This causes the module information given to the guest (MB, or PVH) to have
    incorrect sizes; specifically, sizes rounded up to the next page.
    
    This in turn is problematic for Xen.  When Xen finds a gzipped module, it
    peeks at the end metadata to judge the decompressed size, which is a -4
    backreference from the reported end of the module.
    
    Fill in seg->vend using the correct number of bytes.
    
    Fixes: ea7c8a3d0e82 ("libxc: reorganize domain builder guest memory 
allocator")
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    master commit: 4c3a618b0adaa0cd59e0fa0898bb60978b8b3a5f
    master date: 2024-07-02 10:50:18 +0100
---
 tools/libs/guest/xg_dom_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/libs/guest/xg_dom_core.c b/tools/libs/guest/xg_dom_core.c
index c4f4e7f3e2..f5521d528b 100644
--- a/tools/libs/guest/xg_dom_core.c
+++ b/tools/libs/guest/xg_dom_core.c
@@ -601,7 +601,7 @@ int xc_dom_alloc_segment(struct xc_dom_image *dom,
     memset(ptr, 0, pages * page_size);
 
     seg->vstart = start;
-    seg->vend = dom->virt_alloc_end;
+    seg->vend = start + size;
 
     DOMPRINTF("%-20s:   %-12s : 0x%" PRIx64 " -> 0x%" PRIx64
               "  (pfn 0x%" PRIpfn " + 0x%" PRIpfn " pages)",
--
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