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Intel: x86/sgx: Drop racy follow_pfn() check 

commit dc9b7be557ca94301ea5c06c0d72307e642ffb18 upstream
Backport summary: backport to kernel 5.4.49 for SGX Foundations support

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:

  https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vetter@ffwll.ch/

Fixes: 947c6e11fa43 ("x86/sgx: Add ptrace() support for the SGX driver")
Reported-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/20210204184519.2809313-1-daniel.vetter@ffwll.ch
Signed-off-by: Fan Du <fan.du@intel.com>
This commit is contained in:
Daniel Vetter 2021-02-04 19:45:19 +01:00 committed by kaixuxiakx
parent ae3a3a441f
commit dfdfddc3c7
1 changed files with 0 additions and 8 deletions
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8
arch/x86/kernel/cpu/sgx/encl.c
View File

@ -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);