[RFC PATCH v2 15/19] heki: x86: Initialize permissions counters for pages in vmap()/vunmap()

["Mickaël Salaün" <mic@digikod.net>]

From: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>

When a page gets mapped, create permissions counters for it and
initialize them based on the specified permissions.

When a page gets unmapped, update the counters appropriately.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mickaël Salaün <mic@digikod.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---

Changes since v1:
* New patch
---
 include/linux/heki.h | 11 ++++++++++-
 mm/vmalloc.c         |  7 +++++++
 virt/heki/counters.c | 20 ++++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/include/linux/heki.h b/include/linux/heki.h
index 86c787d121e0..d660994d34d0 100644
--- a/include/linux/heki.h
+++ b/include/linux/heki.h
@@ -68,7 +68,11 @@ struct heki_hypervisor {
  * pointer into this heki structure.
  *
  * During guest kernel boot, permissions counters for each guest page are
- * initialized based on the page's current permissions.
+ * initialized based on the page's current permissions. Beyond this point,
+ * the counters are updated whenever:
+ *
+ *	- a page is mapped into the kernel address space
+ *	- a page is unmapped from the kernel address space
  */
 struct heki {
 	struct heki_hypervisor *hypervisor;
@@ -77,6 +81,7 @@ struct heki {
 
 enum heki_cmd {
 	HEKI_MAP,
+	HEKI_UNMAP,
 };
 
 /*
@@ -109,6 +114,7 @@ void heki_counters_init(void);
 void heki_walk(unsigned long va, unsigned long va_end, heki_func_t func,
 	       struct heki_args *args);
 void heki_map(unsigned long va, unsigned long end);
+void heki_unmap(unsigned long va, unsigned long end);
 
 /* Arch-specific functions. */
 void heki_arch_early_init(void);
@@ -125,6 +131,9 @@ static inline void heki_late_init(void)
 static inline void heki_map(unsigned long va, unsigned long end)
 {
 }
+static inline void heki_unmap(unsigned long va, unsigned long end)
+{
+}
 
 #endif /* CONFIG_HEKI */
 
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a3fedb3ee0db..d9096502e571 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -40,6 +40,7 @@
 #include <linux/pgtable.h>
 #include <linux/hugetlb.h>
 #include <linux/sched/mm.h>
+#include <linux/heki.h>
 #include <asm/tlbflush.h>
 #include <asm/shmparam.h>
 
@@ -301,6 +302,8 @@ static int vmap_range_noflush(unsigned long addr, unsigned long end,
 	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
 		arch_sync_kernel_mappings(start, end);
 
+	heki_map(start, end);
+
 	return err;
 }
 
@@ -419,6 +422,8 @@ void __vunmap_range_noflush(unsigned long start, unsigned long end)
 	pgtbl_mod_mask mask = 0;
 
 	BUG_ON(addr >= end);
+	heki_unmap(start, end);
+
 	pgd = pgd_offset_k(addr);
 	do {
 		next = pgd_addr_end(addr, end);
@@ -564,6 +569,8 @@ static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,
 	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
 		arch_sync_kernel_mappings(start, end);
 
+	heki_map(start, end);
+
 	return 0;
 }
 
diff --git a/virt/heki/counters.c b/virt/heki/counters.c
index 7067449cabca..adc8d566b8a9 100644
--- a/virt/heki/counters.c
+++ b/virt/heki/counters.c
@@ -88,6 +88,13 @@ void heki_callback(struct heki_args *args)
 			heki_update_counters(counters, 0, permissions, 0);
 			break;
 
+		case HEKI_UNMAP:
+			if (WARN_ON_ONCE(!counters))
+				break;
+			heki_update_counters(counters, permissions, 0,
+					     permissions);
+			break;
+
 		default:
 			WARN_ON_ONCE(1);
 			break;
@@ -124,6 +131,19 @@ void heki_map(unsigned long va, unsigned long end)
 	heki_func(va, end, &args);
 }
 
+/*
+ * Find the mappings in the given range and revert the permission counters for
+ * them.
+ */
+void heki_unmap(unsigned long va, unsigned long end)
+{
+	struct heki_args args = {
+		.cmd = HEKI_UNMAP,
+	};
+
+	heki_func(va, end, &args);
+}
+
 /*
  * Permissions counters are associated with each guest page using the
  * Memory Table feature. Initialize the permissions counters here.
-- 
2.42.1