linux-kernel - [PATCH v3 1/3] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Fri,  5 Jan 2024 10:30:23 -0800
From: mhkelley58@...il.com
To: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	kirill.shutemov@...ux.intel.com,
	haiyangz@...rosoft.com,
	wei.liu@...nel.org,
	decui@...rosoft.com,
	luto@...nel.org,
	peterz@...radead.org,
	akpm@...ux-foundation.org,
	urezki@...il.com,
	hch@...radead.org,
	lstoakes@...il.com,
	thomas.lendacky@....com,
	ardb@...nel.org,
	jroedel@...e.de,
	seanjc@...gle.com,
	rick.p.edgecombe@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com,
	linux-kernel@...r.kernel.org,
	linux-coco@...ts.linux.dev,
	linux-hyperv@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH v3 1/3] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback

From: Michael Kelley <mhklinux@...look.com>

In preparation for temporarily marking pages not present during a
transition between encrypted and decrypted, use slow_virt_to_phys()
in the hypervisor callback. As long as the PFN is correct,
slow_virt_to_phys() works even if the leaf PTE is not present.
The existing functions that depend on vmalloc_to_page() all
require that the leaf PTE be marked present, so they don't work.

Update the comments for slow_virt_to_phys() to note this broader usage
and the requirement to work even if the PTE is not marked present.

Signed-off-by: Michael Kelley <mhklinux@...look.com>
---
 arch/x86/hyperv/ivm.c        |  9 ++++++++-
 arch/x86/mm/pat/set_memory.c | 13 +++++++++----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 02e55237d919..8ba18635e338 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -524,7 +524,14 @@ static bool hv_vtom_set_host_visibility(unsigned long kbuffer, int pagecount, bo
 		return false;
 
 	for (i = 0, pfn = 0; i < pagecount; i++) {
-		pfn_array[pfn] = virt_to_hvpfn((void *)kbuffer + i * HV_HYP_PAGE_SIZE);
+		/*
+		 * Use slow_virt_to_phys() because the PRESENT bit has been
+		 * temporarily cleared in the PTEs.  slow_virt_to_phys() works
+		 * without the PRESENT bit while virt_to_hvpfn() or similar
+		 * does not.
+		 */
+		pfn_array[pfn] = slow_virt_to_phys((void *)kbuffer +
+					i * HV_HYP_PAGE_SIZE) >> HV_HYP_PAGE_SHIFT;
 		pfn++;
 
 		if (pfn == HV_MAX_MODIFY_GPA_REP_COUNT || i == pagecount - 1) {
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index bda9f129835e..8e19796e7ce5 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -755,10 +755,15 @@ pmd_t *lookup_pmd_address(unsigned long address)
  * areas on 32-bit NUMA systems.  The percpu areas can
  * end up in this kind of memory, for instance.
  *
- * This could be optimized, but it is only intended to be
- * used at initialization time, and keeping it
- * unoptimized should increase the testing coverage for
- * the more obscure platforms.
+ * It is also used in callbacks for CoCo VM page transitions between private
+ * and shared because it works when the PRESENT bit is not set in the leaf
+ * PTE. In such cases, the state of the PTEs, including the PFN, is otherwise
+ * known to be valid, so the returned physical address is correct. The similar
+ * function vmalloc_to_pfn() can't be used because it requires the PRESENT bit.
+ *
+ * This could be optimized, but it is only used in paths that are not perf
+ * sensitive, and keeping it unoptimized should increase the testing coverage
+ * for the more obscure platforms.
  */
 phys_addr_t slow_virt_to_phys(void *__virt_addr)
 {
-- 
2.25.1