[xen stable-4.21] EFI: refine cfgfile buffer allocation

[patchbot@xxxxxxx]

commit 19c8f4d083e4ba53d88219f97748d2037be200cb
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Oct 29 13:23:39 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Oct 29 13:23:39 2026 +0100

    EFI: refine cfgfile buffer allocation
    
    Use of AllocateMaxAddress requires that the variable pointed to by the
    last argument of ->AllocatePages() is initialized. For cfgfile buffers we
    don't need AllocateMaxAddress though, at which point initialization of
    "addr" also isn't necessary anymore.
    
    Mirror the lack of address constraint also to the main / central buffer
    allocation in read_file().
    
    Fixes: df75f77092c1 ("EFI: avoid OOB config file reads")
    Assisted-by: Sashiko + Opus 5.0
    Reported-by: George Dunlap <dunlapg@xxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
    master commit: cf76c4b8c79ffacbb171468900a7da7d0b1693dc
    master date: 2026-10-06 08:14:43 +0200
---
 xen/common/efi/boot.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index b3df99fc8d..a150ecbf09 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -853,8 +853,13 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, 
CHAR16 *name,
     what = L"Allocation";
     file->addr = min(1UL << (32 + PAGE_SHIFT),
                      HYPERVISOR_VIRT_END - DIRECTMAP_VIRT_START);
-    /* For config files allocate an extra byte to put a NUL there. */
-    ret = efi_bs->AllocatePages(AllocateMaxAddress, EfiLoaderData,
+    /*
+     * For config files allocate an extra byte to put a NUL there.  There's
+     * also no constraint on addresses for them.
+     */
+    ret = efi_bs->AllocatePages(file != &cfg ? AllocateMaxAddress
+                                             : AllocateAnyPages,
+                                EfiLoaderData,
                                 PFN_UP(size + (file == &cfg)), &file->addr);
     if ( EFI_ERROR(ret) )
         goto fail;
@@ -906,7 +911,7 @@ static bool __init read_section(const EFI_LOADED_IMAGE 
*image,
     if ( file == &cfg && file->size && !iscntrl(file->str[file->size - 1]) )
     {
         EFI_PHYSICAL_ADDRESS addr;
-        EFI_STATUS ret = efi_bs->AllocatePages(AllocateMaxAddress,
+        EFI_STATUS ret = efi_bs->AllocatePages(AllocateAnyPages,
                                                EfiLoaderData,
                                                PFN_UP(file->size + 1), &addr);
 
--
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