[PATCH for_v22 01/11] x86/sgx: Fix an SECS collision with enclave page at VA=0

[Sean Christopherson <sean.j.christopherson@intel.com>]

Detect the SECS in paging related flows by explicitly checking the page
against the enclave's SECS page.  Assuming a page with VA=0 is the SECS
will break enclaves that actually use VA=0, which is extremely unlikely
but theoretically possible.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kernel/cpu/sgx/encl.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 909af9a664f0..6da1c36a01e6 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -12,10 +12,14 @@
 #include "encls.h"
 #include "sgx.h"
 
+static bool sgx_encl_is_secs(struct sgx_encl *encl, struct sgx_encl_page *page)
+{
+	return page == &encl->secs;
+}
+
 static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
 			   struct sgx_epc_page *epc_page)
 {
-	unsigned long addr = SGX_ENCL_PAGE_ADDR(encl_page);
 	unsigned long va_offset = SGX_ENCL_PAGE_VA_OFFSET(encl_page);
 	struct sgx_encl *encl = encl_page->encl;
 	pgoff_t page_index = sgx_encl_get_index(encl, encl_page);
@@ -38,11 +42,11 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
 		goto err_pcmd;
 	}
 
-	pginfo.addr = addr;
+	pginfo.addr = SGX_ENCL_PAGE_ADDR(encl_page);
 	pginfo.contents = (unsigned long)kmap_atomic(backing);
 	pginfo.metadata = (unsigned long)kmap_atomic(pcmd) + pcmd_offset;
-	pginfo.secs = addr ? (unsigned long)sgx_epc_addr(encl->secs.epc_page) :
-		      0;
+	pginfo.secs = sgx_encl_is_secs(encl, encl_page) ? 0 :
+			(unsigned long)sgx_epc_addr(encl->secs.epc_page);
 
 	ret = __eldu(&pginfo, sgx_epc_addr(epc_page),
 		     sgx_epc_addr(encl_page->va_page->epc_page) + va_offset);
@@ -546,7 +550,7 @@ void sgx_encl_release(struct kref *ref)
  */
 pgoff_t sgx_encl_get_index(struct sgx_encl *encl, struct sgx_encl_page *page)
 {
-	if (!PFN_DOWN(page->desc))
+	if (sgx_encl_is_secs(encl, page))
 		return PFN_DOWN(encl->size);
 
 	return PFN_DOWN(page->desc - encl->base);
-- 
2.22.0