x86/kasan: Map shadow for percpu pages on demand

KASAN maps shadow for the entire CPU-entry-area:
  [CPU_ENTRY_AREA_BASE, CPU_ENTRY_AREA_BASE + CPU_ENTRY_AREA_MAP_SIZE]

This will explode once the per-cpu entry areas are randomized since it
will increase CPU_ENTRY_AREA_MAP_SIZE to 512 GB and KASAN fails to
allocate shadow for such big area.

Fix this by allocating KASAN shadow only for really used cpu entry area
addresses mapped by cea_map_percpu_pages()

Thanks to the 0day folks for finding and reporting this to be an issue.

[ dhansen: tweak changelog since this will get committed before peterz's
	   actual cpu-entry-area randomization ]

Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Yujie Liu <yujie.liu@intel.com>
Cc: kernel test robot <yujie.liu@intel.com>
Link: https://lore.kernel.org/r/202210241508.2e203c3d-yujie.liu@intel.com

3 files changed, 22 insertions, 4 deletions

diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
index 13e70da38bed..de75306b932e 100644
--- a/arch/x86/include/asm/kasan.h
+++ b/arch/x86/include/asm/kasan.h
@@ -28,9 +28,12 @@
 #ifdef CONFIG_KASAN
 void __init kasan_early_init(void);
 void __init kasan_init(void);
+void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid);
 #else
 static inline void kasan_early_init(void) { }
 static inline void kasan_init(void) { }
+static inline void kasan_populate_shadow_for_vaddr(void *va, size_t size,
+						   int nid) { }
 #endif
 
 #endif
diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index 6c2f1b76a0b6..d7081b1accca 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -9,6 +9,7 @@
 #include <asm/cpu_entry_area.h>
 #include <asm/fixmap.h>
 #include <asm/desc.h>
+#include <asm/kasan.h>
 
 static DEFINE_PER_CPU_PAGE_ALIGNED(struct entry_stack_page, entry_stack_storage);
 
@@ -53,8 +54,13 @@ void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags)
 static void __init
 cea_map_percpu_pages(void *cea_vaddr, void *ptr, int pages, pgprot_t prot)
 {
+	phys_addr_t pa = per_cpu_ptr_to_phys(ptr);
+
+	kasan_populate_shadow_for_vaddr(cea_vaddr, pages * PAGE_SIZE,
+					early_pfn_to_nid(PFN_DOWN(pa)));
+
 	for ( ; pages; pages--, cea_vaddr+= PAGE_SIZE, ptr += PAGE_SIZE)
-		cea_set_pte(cea_vaddr, per_cpu_ptr_to_phys(ptr), prot);
+		cea_set_pte(cea_vaddr, pa, prot);
 }
 
 static void __init percpu_setup_debug_store(unsigned int cpu)
diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index e7b9b464a82f..d1416926ad52 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -316,6 +316,18 @@ void __init kasan_early_init(void)
 	kasan_map_early_shadow(init_top_pgt);
 }
 
+void __init kasan_populate_shadow_for_vaddr(void *va, size_t size, int nid)
+{
+	unsigned long shadow_start, shadow_end;
+
+	shadow_start = (unsigned long)kasan_mem_to_shadow(va);
+	shadow_start = round_down(shadow_start, PAGE_SIZE);
+	shadow_end = (unsigned long)kasan_mem_to_shadow(va + size);
+	shadow_end = round_up(shadow_end, PAGE_SIZE);
+
+	kasan_populate_shadow(shadow_start, shadow_end, nid);
+}
+
 void __init kasan_init(void)
 {
 	int i;
@@ -393,9 +405,6 @@ void __init kasan_init(void)
 		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
 		shadow_cpu_entry_begin);
 
-	kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
-			      (unsigned long)shadow_cpu_entry_end, 0);
-
 	kasan_populate_early_shadow(shadow_cpu_entry_end,
 			kasan_mem_to_shadow((void *)__START_KERNEL_map));