PTE insertion is fundamentally racy, and this check doesn't do anything useful. Quoting Sean: "Yeah, it can be whacked. The original, never-upstreamed code asserted that the resolved PFN matched the PFN being installed by the fault handler as a sanity check on the SGX driver's EPC management. The WARN assertion got dropped for whatever reason, leaving that useless chunk." Jason stumbled over this as a new user of follow_pfn, and I'm trying to get rid of unsafe callers of that function so it can be locked down further. This is independent prep work for the referenced patch series. References: https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vetter@xxxxxxxx/ Reported-by: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Sean Christopherson <seanjc@xxxxxxxxxx> Fixes: 947c6e11fa43 ("x86/sgx: Add ptrace() support for the SGX driver") Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxx> Cc: linux-sgx@xxxxxxxxxxxxxxx Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> --- arch/x86/kernel/cpu/sgx/encl.c | 8 -------- 1 file changed, 8 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index ee50a5010277..20a2dd5ba2b4 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -141,7 +141,6 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf) struct sgx_encl_page *entry; unsigned long phys_addr; struct sgx_encl *encl; - unsigned long pfn; vm_fault_t ret; encl = vma->vm_private_data; @@ -168,13 +167,6 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf) phys_addr = sgx_get_epc_phys_addr(entry->epc_page); - /* Check if another thread got here first to insert the PTE. */ - if (!follow_pfn(vma, addr, &pfn)) { - mutex_unlock(&encl->lock); - - return VM_FAULT_NOPAGE; - } - ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr)); if (ret != VM_FAULT_NOPAGE) { mutex_unlock(&encl->lock); -- 2.30.0
