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Mingyu Wang
ce800993af
commitb08472db93upstream. A NULL pointer dereference was observed in the AMD64 AGP driver when running in a virtualized environment (e.g. qemu/kvm) without a physical AMD northbridge. The crash occurs in amd64_fetch_size() when attempting to dereference the pointer returned by node_to_amd_nb(0). The root cause of this crash is broken error propagation in agp_amd64_probe(): When no AMD northbridges are found, cache_nbs() correctly returns -ENODEV. However, the probe function erroneously checks the return value against exactly -1, rather than < 0. As a result, the hardware absence error is masked, allowing the driver to improperly proceed with initialization. It eventually calls agp_add_bridge(), which invokes amd64_fetch_size(). Since the hardware does not exist, node_to_amd_nb(0) returns NULL, leading to a General Protection Fault (GPF) when accessing its ->misc member. Fix the issue by correcting the error check in agp_amd64_probe() to abort properly when cache_nbs() returns any negative error code. This prevents the driver from erroneously proceeding without hardware, thereby avoiding the subsequent NULL pointer dereference at its source. Fixes:a32073bffc("[PATCH] x86_64: Clean and enhance up K8 northbridge access code") Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> Signed-off-by: Lukas Wunner <lukas@wunner.de> Reviewed-by: Lukas Wunner <lukas@wunner.de> Cc: stable@vger.kernel.org # v2.6.18+ Link: https://patch.msgid.link/20260504074823.99377-1-w15303746062@163.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>