A PCMD (Paging Crypto MetaData) page contains the PCMD structures of enclave pages that have been encrypted and moved to the shmem backing store. When all enclave pages sharing a PCMD page are loaded in the enclave, there is no need for the PCMD page and it can be truncated from the backing store.
A few issues appeared around the truncation of PCMD pages. The known issues have been addressed but the PCMD handling code could be made more robust by loudly complaining if any new issue appears in this area.
Add a check that will complain with a warning if the PCMD page is not actually empty after it has been truncated. There should never be data in the PCMD page at this point since it is was just checked to be empty and truncated with enclave mutex held and is updated with the enclave mutex held.
Suggested-by: Dave Hansen dave.hansen@linux.intel.com Tested-by: Haitao Huang haitao.huang@intel.com Signed-off-by: Reinette Chatre reinette.chatre@intel.com --- Changes since V2: - Change WARN_ON_ONCE() to pr_warn(). (Jarkko). - Add Haitao's Tested-by tag.
Changes since RFC v1: - New patch.
arch/x86/kernel/cpu/sgx/encl.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index 243f3bd78145..3c24e6124d95 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -187,12 +187,20 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page, kunmap_atomic(pcmd_page); kunmap_atomic((void *)(unsigned long)pginfo.contents);
+ get_page(b.pcmd); sgx_encl_put_backing(&b);
sgx_encl_truncate_backing_page(encl, page_index);
- if (pcmd_page_empty && !reclaimer_writing_to_pcmd(encl, pcmd_first_page)) + if (pcmd_page_empty && !reclaimer_writing_to_pcmd(encl, pcmd_first_page)) { sgx_encl_truncate_backing_page(encl, PFN_DOWN(page_pcmd_off)); + pcmd_page = kmap_atomic(b.pcmd); + if (memchr_inv(pcmd_page, 0, PAGE_SIZE)) + pr_warn("PCMD page not empty after truncate.\n"); + kunmap_atomic(pcmd_page); + } + + put_page(b.pcmd);
return ret; }