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b408b52e71
Add a regression (and proof-of-bug) testcase to ensure KVM rejects an offset+size that would result in a negative value when computed as a signed 64-bit value. KVM had a flaw where it would allow binding a memslot to a guest_memfd instance even with a wildly out-of-range offset, if the offset and size were both positive values, but the combined offset+size was negative. Use "0x7fffffffffffffffull - page_size", i.e. "INT64_MAX - page_size", for the offset as the size of the guest_memfd file must be at least page_size (KVM requires memslots and gmem files to be host page-size aligned). I.e. "INT64_MAX - page_size + size" is guaranteed to generate an offset+size that is negative when converted to a signed 64-bit value *and* honors KVM's alignment requirements. Reviewed-by: Ackerley Tng <ackerleytng@google.com> Tested-by: Ackerley Tng <ackerleytng@google.com> Link: https://patch.msgid.link/20260602170921.1304394-4-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>