[v3,07/14] x86: KASAN raw shadow memory PTE init

Commit Message

Maciej Wieczor-Retman April 4, 2025, 1:14 p.m. UTC

In KASAN's generic mode the default value in shadow memory is zero.
During initialization of shadow memory pages they are allocated and
zeroed.

In KASAN's tag-based mode the default tag for the arm64 architecture is
0xFE which corresponds to any memory that should not be accessed. On x86
(where tags are 4-bit wide instead of 8-bit wide) that tag is 0xE so
during the initializations all the bytes in shadow memory pages should
be filled with 0xE.

Use memblock_alloc_try_nid_raw() instead of memblock_alloc_try_nid() to
avoid zeroing out the memory so it can be set with the KASAN invalid
tag.

Signed-off-by: Maciej Wieczor-Retman <[e-mail]>
---
Changelog v2:
- Remove dense mode references, use memset() instead of kasan_poison().

 arch/x86/mm/kasan_init_64.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

Patch

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 0539efd0d216..e8a451cafc8c 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -34,6 +34,18 @@  static __init void *early_alloc(size_t size, int nid, bool should_panic)
 	return ptr;
 }
 
+static __init void *early_raw_alloc(size_t size, int nid, bool should_panic)
+{
+	void *ptr = memblock_alloc_try_nid_raw(size, size,
+			__pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_ACCESSIBLE, nid);
+
+	if (!ptr && should_panic)
+		panic("%pS: Failed to allocate page, nid=%d from=%lx\n",
+		      (void *)_RET_IP_, nid, __pa(MAX_DMA_ADDRESS));
+
+	return ptr;
+}
+
 static void __init kasan_populate_pmd(pmd_t *pmd, unsigned long addr,
 				      unsigned long end, int nid)
 {
@@ -63,8 +75,9 @@  static void __init kasan_populate_pmd(pmd_t *pmd, unsigned long addr,
 		if (!pte_none(*pte))
 			continue;
 
-		p = early_alloc(PAGE_SIZE, nid, true);
-		entry = pfn_pte(PFN_DOWN(__pa(p)), PAGE_KERNEL);
+		p = early_raw_alloc(PAGE_SIZE, nid, true);
+		memset(p, PAGE_SIZE, KASAN_SHADOW_INIT);
+		entry = pfn_pte(PFN_DOWN(__pa_nodebug(p)), PAGE_KERNEL);
 		set_pte_at(&init_mm, addr, pte, entry);
 	} while (pte++, addr += PAGE_SIZE, addr != end);
 }
@@ -436,7 +449,7 @@  void __init kasan_init(void)
 	 * it may contain some garbage. Now we can clear and write protect it,
 	 * since after the TLB flush no one should write to it.
 	 */
-	memset(kasan_early_shadow_page, 0, PAGE_SIZE);
+	memset(kasan_early_shadow_page, KASAN_SHADOW_INIT, PAGE_SIZE);
 	for (i = 0; i < PTRS_PER_PTE; i++) {
 		pte_t pte;
 		pgprot_t prot;