[xen master] xen/memory: Make resource_max_frames() to return 0 on unknown type

[patchbot@xxxxxxx]

commit 9b8708290002f0a4d0b363e0c66ce945f6b520bd
Author:     Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
AuthorDate: Tue Feb 18 00:34:02 2025 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Feb 18 14:47:34 2025 +0000

    xen/memory: Make resource_max_frames() to return 0 on unknown type
    
    This is actually what the caller acquire_resource() expects on any kind
    of error (the comment on top of resource_max_frames() also suggests that).
    Otherwise, the caller will treat -errno as a valid value and propagate 
incorrect
    nr_frames to the VM. As a possible consequence, a VM trying to query a 
resource
    size of an unknown type will get the success result from the hypercall and 
obtain
    nr_frames 4294967201.
    
    Also, add an ASSERT_UNREACHABLE() in the default case of 
_acquire_resource(),
    normally we won't get to this point, as an unknown type will always be 
rejected
    earlier in resource_max_frames().
    
    Also, update test-resource app to verify that Xen can deal with invalid
    (unknown) resource type properly.
    
    Fixes: 9244528955de ("xen/memory: Fix acquire_resource size semantics")
    Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 tools/tests/resource/test-resource.c | 10 ++++++++++
 xen/common/memory.c                  |  3 ++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/tests/resource/test-resource.c 
b/tools/tests/resource/test-resource.c
index 1b10be16a6..a7f2d04643 100644
--- a/tools/tests/resource/test-resource.c
+++ b/tools/tests/resource/test-resource.c
@@ -123,6 +123,16 @@ static void test_gnttab(uint32_t domid, unsigned int 
nr_frames,
         fail("    Fail: Managed to map gnttab v2 status frames in v1 mode\n");
         xenforeignmemory_unmap_resource(fh, res);
     }
+
+    /*
+     * If this check starts failing, you've found the right place to test your
+     * addition to the Acquire Resource infrastructure.
+     */
+    rc = xenforeignmemory_resource_size(fh, domid, 3, 0, &size);
+
+    /* Check that Xen rejected the resource type. */
+    if ( !rc )
+        fail("    Fail: Expected error on an invalid resource type, got 
success\n");
 }
 
 static void test_domain_configurations(void)
diff --git a/xen/common/memory.c b/xen/common/memory.c
index a6f2f6d1b3..8ca4e1a842 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1157,7 +1157,7 @@ static unsigned int resource_max_frames(const struct 
domain *d,
         return d->vmtrace_size >> PAGE_SHIFT;
 
     default:
-        return -EOPNOTSUPP;
+        return 0;
     }
 }
 
@@ -1240,6 +1240,7 @@ static int _acquire_resource(
         return acquire_vmtrace_buf(d, id, frame, nr_frames, mfn_list);
 
     default:
+        ASSERT_UNREACHABLE();
         return -EOPNOTSUPP;
     }
 }
--
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