arm64: kfence: Avoid NOMAP tricks when mapping the early pool

Now that the map_mem() routines respect existing page mappings and
contiguous granule sized blocks with the contiguous bit cleared, there
is no longer a reason to play tricks with the memblock NOMAP attribute.

Instead, the kfence pool can be allocated and mapped with page
granularity first, and this granularity will be respected when the rest
of DRAM is mapped later, even if block and contiguous mappings are
allowed for the remainder of those mappings.

Add the NO_EXEC_MAPPINGS flag to ensure that hierarchical XN attributes
are set on the intermediate page tables that are allocated when mapping
the pool.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

Author: ardbiesheuvel

arch/arm64/mm/mmu.c

@@ -1083,36 +1083,24 @@ static int __init parse_kfence_early_init(char *arg)
 }
 early_param("kfence.sample_interval", parse_kfence_early_init);
 
-static phys_addr_t __init arm64_kfence_alloc_pool(void)
+static void __init arm64_kfence_map_pool(void)
 {
 	phys_addr_t kfence_pool;
 
 	if (!kfence_early_init)
-		return 0;
+		return;
 
 	kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
 	if (!kfence_pool) {
 		pr_err("failed to allocate kfence pool\n");
 		kfence_early_init = false;
-		return 0;
-	}
-
-	/* Temporarily mark as NOMAP. */
-	memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
-
-	return kfence_pool;
-}
-
-static void __init arm64_kfence_map_pool(phys_addr_t kfence_pool)
-{
-	if (!kfence_pool)
 		return;
+	}
 
 	/* KFENCE pool needs page-level mapping. */
 	__map_memblock(kfence_pool, kfence_pool + KFENCE_POOL_SIZE,
 			pgprot_tagged(PAGE_KERNEL),
-			NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
-	memblock_clear_nomap(kfence_pool, KFENCE_POOL_SIZE);
+			NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS | NO_EXEC_MAPPINGS);
 	__kfence_pool = phys_to_virt(kfence_pool);
 }
 
@@ -1144,8 +1132,7 @@ bool arch_kfence_init_pool(void)
 }
 #else /* CONFIG_KFENCE */
 
-static inline phys_addr_t arm64_kfence_alloc_pool(void) { return 0; }
-static inline void arm64_kfence_map_pool(phys_addr_t kfence_pool) { }
+static inline void arm64_kfence_map_pool(void) { }
 
 #endif /* CONFIG_KFENCE */
 
@@ -1155,7 +1142,6 @@ static void __init map_mem(void)
 	phys_addr_t kernel_start = __pa_symbol(_text);
 	phys_addr_t kernel_end = __pa_symbol(__init_begin);
 	phys_addr_t start, end;
-	phys_addr_t early_kfence_pool;
 	int flags = NO_EXEC_MAPPINGS;
 	u64 i;
 
@@ -1172,7 +1158,7 @@ static void __init map_mem(void)
 	BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end) &&
 		     pgd_index(_PAGE_OFFSET(VA_BITS_MIN)) != PTRS_PER_PGD - 1);
 
-	early_kfence_pool = arm64_kfence_alloc_pool();
+	arm64_kfence_map_pool();
 
 	linear_map_requires_bbml2 = !force_pte_mapping() && can_set_direct_map();
 
@@ -1210,7 +1196,6 @@ static void __init map_mem(void)
 	 */
 	__map_memblock(kernel_start, kernel_end, PAGE_KERNEL, NO_CONT_MAPPINGS);
 	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
-	arm64_kfence_map_pool(early_kfence_pool);
 }
 
 void mark_rodata_ro(void)