linux-kernel - [tip: x86/sgx] x86/sgx: Ensure no data in PCMD page after truncate

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Date:   Tue, 17 May 2022 18:11:59 -0000
From:   "tip-bot2 for Reinette Chatre" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Haitao Huang <haitao.huang@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/sgx] x86/sgx: Ensure no data in PCMD page after truncate

The following commit has been merged into the x86/sgx branch of tip:

Commit-ID:     e3a3bbe3e99de73043a1d32d36cf4d211dc58c7e
Gitweb:        https://git.kernel.org/tip/e3a3bbe3e99de73043a1d32d36cf4d211dc58c7e
Author:        Reinette Chatre <reinette.chatre@...el.com>
AuthorDate:    Thu, 12 May 2022 14:51:01 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Mon, 16 May 2022 15:17:57 -07:00

x86/sgx: Ensure no data in PCMD page after truncate

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@...ux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
Tested-by: Haitao Huang <haitao.huang@...el.com>
Link: https://lkml.kernel.org/r/6495120fed43fafc1496d09dd23df922b9a32709.1652389823.git.reinette.chatre@intel.com
---
 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 243f3bd..3c24e61 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;
 }