[PATCH v3] radix/kfence: map __kfence_pool at page granularity

[PATCH v3] radix/kfence: map __kfence_pool at page granularity

[Hari Bathini]

When KFENCE is enabled, total system memory is mapped at page level
granularity. But in radix MMU mode, ~3GB additional memory is needed
to map 100GB of system memory at page level granularity when compared
to using 2MB direct mapping. This is not desired considering KFENCE is
designed to be enabled in production kernels [1]. Also, mapping only
the memory allocated for KFENCE pool at page granularity is sufficient
to enable KFENCE support. So, allocate __kfence_pool during bootup and
map it at page granularity instead of mapping all system memory at
page granularity.

Without patch:
    # cat /proc/meminfo
    MemTotal:       101201920 kB

With patch:
    # cat /proc/meminfo
    MemTotal:       104483904 kB

Note that enabling KFENCE at runtime is disabled for radix MMU for now,
as it depends on the ability to split page table mappings and such APIs
are not currently implemented for radix MMU.

All kfence_test.c testcases passed with this patch.

[1] https://lore.kernel.org/all/20201103175841.3495947-2-elver@google.com/

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---

Changes in v3:
* Updated the changelog and contained changes relevant for radix MMU
  within radix-pgtable.c as suggested by mpe.

Changes in v2:
* Dropped the patch that adds support to enable KFENCE after startup.
* Added changes to avoid KFENCE enablement after system startup.
* Also, added a TODO explaining why KFENCE enablement after startup
  is not supported for now.
* Functions to alloc/map __kfence_pool as suggested by Ritesh.
* Moved changes that apply to ppc32 as well to common file as suggested
  by Christophe.

 
 arch/powerpc/include/asm/kfence.h        | 11 +++-
 arch/powerpc/mm/book3s64/radix_pgtable.c | 84 ++++++++++++++++++++++--
 arch/powerpc/mm/init-common.c            |  3 +
 3 files changed, 93 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/kfence.h b/arch/powerpc/include/asm/kfence.h
index 424ceef82ae6..fab124ada1c7 100644
--- a/arch/powerpc/include/asm/kfence.h
+++ b/arch/powerpc/include/asm/kfence.h
@@ -15,10 +15,19 @@
 #define ARCH_FUNC_PREFIX "."
 #endif
 
+#ifdef CONFIG_KFENCE
+extern bool kfence_disabled;
+
+static inline void disable_kfence(void)
+{
+	kfence_disabled = true;
+}
+
 static inline bool arch_kfence_init_pool(void)
 {
-	return true;
+	return !kfence_disabled;
 }
+#endif
 
 #ifdef CONFIG_PPC64
 static inline bool kfence_protect_page(unsigned long addr, bool protect)
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index 15e88f1439ec..b0d927009af8 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -17,6 +17,7 @@
 #include <linux/hugetlb.h>
 #include <linux/string_helpers.h>
 #include <linux/memory.h>
+#include <linux/kfence.h>
 
 #include <asm/pgalloc.h>
 #include <asm/mmu_context.h>
@@ -31,6 +32,7 @@
 #include <asm/uaccess.h>
 #include <asm/ultravisor.h>
 #include <asm/set_memory.h>
+#include <asm/kfence.h>
 
 #include <trace/events/thp.h>
 
@@ -293,7 +295,8 @@ static unsigned long next_boundary(unsigned long addr, unsigned long end)
 
 static int __meminit create_physical_mapping(unsigned long start,
 					     unsigned long end,
-					     int nid, pgprot_t _prot)
+					     int nid, pgprot_t _prot,
+					     unsigned long mapping_sz_limit)
 {
 	unsigned long vaddr, addr, mapping_size = 0;
 	bool prev_exec, exec = false;
@@ -301,7 +304,10 @@ static int __meminit create_physical_mapping(unsigned long start,
 	int psize;
 	unsigned long max_mapping_size = memory_block_size;
 
-	if (debug_pagealloc_enabled_or_kfence())
+	if (mapping_sz_limit < max_mapping_size)
+		max_mapping_size = mapping_sz_limit;
+
+	if (debug_pagealloc_enabled())
 		max_mapping_size = PAGE_SIZE;
 
 	start = ALIGN(start, PAGE_SIZE);
@@ -356,8 +362,74 @@ static int __meminit create_physical_mapping(unsigned long start,
 	return 0;
 }
 
+#ifdef CONFIG_KFENCE
+static bool __ro_after_init kfence_early_init = !!CONFIG_KFENCE_SAMPLE_INTERVAL;
+
+static int __init parse_kfence_early_init(char *arg)
+{
+	int val;
+
+	if (get_option(&arg, &val))
+		kfence_early_init = !!val;
+	return 0;
+}
+early_param("kfence.sample_interval", parse_kfence_early_init);
+
+static inline phys_addr_t alloc_kfence_pool(void)
+{
+	phys_addr_t kfence_pool;
+
+	/*
+	 * TODO: Support to enable KFENCE after bootup depends on the ability to
+	 *       split page table mappings. As such support is not currently
+	 *       implemented for radix pagetables, support enabling KFENCE
+	 *       only at system startup for now.
+	 *
+	 *       After support for splitting mappings is available on radix,
+	 *       alloc_kfence_pool() & map_kfence_pool() can be dropped and
+	 *       mapping for __kfence_pool memory can be
+	 *       split during arch_kfence_init_pool().
+	 */
+	if (!kfence_early_init)
+		goto no_kfence;
+
+	kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+	if (!kfence_pool)
+		goto no_kfence;
+
+	memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
+	return kfence_pool;
+
+no_kfence:
+	disable_kfence();
+	return 0;
+}
+
+static inline void map_kfence_pool(phys_addr_t kfence_pool)
+{
+	if (!kfence_pool)
+		return;
+
+	if (create_physical_mapping(kfence_pool, kfence_pool + KFENCE_POOL_SIZE,
+				    -1, PAGE_KERNEL, PAGE_SIZE))
+		goto err;
+
+	memblock_clear_nomap(kfence_pool, KFENCE_POOL_SIZE);
+	__kfence_pool = __va(kfence_pool);
+	return;
+
+err:
+	memblock_phys_free(kfence_pool, KFENCE_POOL_SIZE);
+	disable_kfence();
+}
+#else
+static inline phys_addr_t alloc_kfence_pool(void) { return 0; }
+static inline void map_kfence_pool(phys_addr_t kfence_pool) { }
+#endif
+
 static void __init radix_init_pgtable(void)
 {
+	phys_addr_t kfence_pool;
 	unsigned long rts_field;
 	phys_addr_t start, end;
 	u64 i;
@@ -365,6 +437,8 @@ static void __init radix_init_pgtable(void)
 	/* We don't support slb for radix */
 	slb_set_size(0);
 
+	kfence_pool = alloc_kfence_pool();
+
 	/*
 	 * Create the linear mapping
 	 */
@@ -381,9 +455,11 @@ static void __init radix_init_pgtable(void)
 		}
 
 		WARN_ON(create_physical_mapping(start, end,
-						-1, PAGE_KERNEL));
+						-1, PAGE_KERNEL, ~0UL));
 	}
 
+	map_kfence_pool(kfence_pool);
+
 	if (!cpu_has_feature(CPU_FTR_HVMODE) &&
 			cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) {
 		/*
@@ -875,7 +951,7 @@ int __meminit radix__create_section_mapping(unsigned long start,
 	}
 
 	return create_physical_mapping(__pa(start), __pa(end),
-				       nid, prot);
+				       nid, prot, ~0UL);
 }
 
 int __meminit radix__remove_section_mapping(unsigned long start, unsigned long end)
diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index d3a7726ecf51..21131b96d209 100644
--- a/arch/powerpc/mm/init-common.c
+++ b/arch/powerpc/mm/init-common.c
@@ -31,6 +31,9 @@ EXPORT_SYMBOL_GPL(kernstart_virt_addr);
 
 bool disable_kuep = !IS_ENABLED(CONFIG_PPC_KUEP);
 bool disable_kuap = !IS_ENABLED(CONFIG_PPC_KUAP);
+#ifdef CONFIG_KFENCE
+bool __ro_after_init kfence_disabled;
+#endif
 
 static int __init parse_nosmep(char *p)
 {
-- 
2.45.1

Re: [PATCH v3] radix/kfence: map __kfence_pool at page granularity

[Michael Ellerman]

On Mon, 01 Jul 2024 18:30:21 +0530, Hari Bathini wrote:
> When KFENCE is enabled, total system memory is mapped at page level
> granularity. But in radix MMU mode, ~3GB additional memory is needed
> to map 100GB of system memory at page level granularity when compared
> to using 2MB direct mapping. This is not desired considering KFENCE is
> designed to be enabled in production kernels [1]. Also, mapping only
> the memory allocated for KFENCE pool at page granularity is sufficient
> to enable KFENCE support. So, allocate __kfence_pool during bootup and
> map it at page granularity instead of mapping all system memory at
> page granularity.
> 
> [...]

Applied to powerpc/next.

[1/1] radix/kfence: map __kfence_pool at page granularity
      https://git.kernel.org/powerpc/c/353d7a84c214f184d5a6b62acdec8b4424159b7c

cheers