[PATCH v9] mm,kfence: decouple kfence from page granularity mapping judgement
Marco Elver
elver at google.com
Thu Mar 16 03:06:50 PDT 2023
On Thu, Mar 16, 2023 at 04:50PM +0800, Zhenhua Huang wrote:
> Kfence only needs its pool to be mapped as page granularity, if it is
> inited early. Previous judgement was a bit over protected. From [1], Mark
> suggested to "just map the KFENCE region a page granularity". So I
> decouple it from judgement and do page granularity mapping for kfence
> pool only. Need to be noticed that late init of kfence pool still requires
> page granularity mapping.
>
> Page granularity mapping in theory cost more(2M per 1GB) memory on arm64
> platform. Like what I've tested on QEMU(emulated 1GB RAM) with
> gki_defconfig, also turning off rodata protection:
> Before:
> [root at liebao ]# cat /proc/meminfo
> MemTotal: 999484 kB
> After:
> [root at liebao ]# cat /proc/meminfo
> MemTotal: 1001480 kB
>
> To implement this, also relocate the kfence pool allocation before the
> linear mapping setting up, arm64_kfence_alloc_pool is to allocate phys
> addr, __kfence_pool is to be set after linear mapping set up.
>
> LINK: [1] https://lore.kernel.org/linux-arm-kernel/Y+IsdrvDNILA59UN@FVFF77S0Q05N/
> Suggested-by: Mark Rutland <mark.rutland at arm.com>
> Signed-off-by: Zhenhua Huang <quic_zhenhuah at quicinc.com>
> ---
> arch/arm64/include/asm/kfence.h | 16 +++++++++++
> arch/arm64/mm/mmu.c | 59 +++++++++++++++++++++++++++++++++++++++++
> arch/arm64/mm/pageattr.c | 9 +++++--
> include/linux/kfence.h | 1 +
> mm/kfence/core.c | 4 +++
> 5 files changed, 87 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
> index aa855c6..8143c91 100644
> --- a/arch/arm64/include/asm/kfence.h
> +++ b/arch/arm64/include/asm/kfence.h
> @@ -10,6 +10,22 @@
>
> #include <asm/set_memory.h>
>
> +extern phys_addr_t early_kfence_pool;
This should not be accessible if !CONFIG_KFENCE.
> +#ifdef CONFIG_KFENCE
> +
> +extern char *__kfence_pool;
> +static inline void kfence_set_pool(phys_addr_t addr)
> +{
> + __kfence_pool = phys_to_virt(addr);
> +}
kfence_set_pool() is redundant if it's for arm64 only, because we know
where it's needed, and there you could just access __kfence_pool
directly. So let's just remove this function. (Initially I thought you
want to provide it generally, also for other architectures.)
> +#else
> +
> +static inline void kfence_set_pool(phys_addr_t addr) { }
> +
> +#endif
> +
> static inline bool arch_kfence_init_pool(void) { return true; }
[...]
> +#endif
> +
> +phys_addr_t early_kfence_pool;
This variable now exists in non-KFENCE builds, which is wrong.
> static void __init map_mem(pgd_t *pgdp)
> {
> static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
> @@ -543,6 +587,10 @@ static void __init map_mem(pgd_t *pgdp)
> */
> BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end));
>
> + early_kfence_pool = arm64_kfence_alloc_pool();
> + if (early_kfence_pool)
> + memblock_mark_nomap(early_kfence_pool, KFENCE_POOL_SIZE);
> +
> if (can_set_direct_map())
> flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>
> @@ -608,6 +656,17 @@ static void __init map_mem(pgd_t *pgdp)
> }
> }
> #endif
> +
> + /* Kfence pool needs page-level mapping */
> + if (early_kfence_pool) {
> + __map_memblock(pgdp, early_kfence_pool,
> + early_kfence_pool + KFENCE_POOL_SIZE,
> + pgprot_tagged(PAGE_KERNEL),
> + NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
> + memblock_clear_nomap(early_kfence_pool, KFENCE_POOL_SIZE);
> + /* kfence_pool really mapped now */
> + kfence_set_pool(early_kfence_pool);
> + }
This whole piece of code could also be wrapped in another function,
which becomes a no-op if !CONFIG_KFENCE. Then you also don't need to
provide the KFENCE_POOL_SIZE define for 0 if !CONFIG_KFENCE.
[...]
> + *
> + * Kfence pool requires page granularity mapping also if we init it
> + * late.
> */
> return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
> - IS_ENABLED(CONFIG_KFENCE);
> + (IS_ENABLED(CONFIG_KFENCE) && !early_kfence_pool);
Accessing a non-existent variable if !CONFIG_KFENCE works because the
compiler optimizes out the access, but is generally bad style.
I think the only issue that I have is that the separation between KFENCE
and non-KFENCE builds is not great.
At the end of the email are is a diff against your patch which would be
my suggested changes (while at it, I fixed up a bunch of other issues).
Untested, so if you decide to adopt these changes, please test.
Thanks,
-- Marco
------ >8 ------
diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
index 8143c91854e1..a81937fae9f6 100644
--- a/arch/arm64/include/asm/kfence.h
+++ b/arch/arm64/include/asm/kfence.h
@@ -10,22 +10,6 @@
#include <asm/set_memory.h>
-extern phys_addr_t early_kfence_pool;
-
-#ifdef CONFIG_KFENCE
-
-extern char *__kfence_pool;
-static inline void kfence_set_pool(phys_addr_t addr)
-{
- __kfence_pool = phys_to_virt(addr);
-}
-
-#else
-
-static inline void kfence_set_pool(phys_addr_t addr) { }
-
-#endif
-
static inline bool arch_kfence_init_pool(void) { return true; }
static inline bool kfence_protect_page(unsigned long addr, bool protect)
@@ -35,4 +19,14 @@ static inline bool kfence_protect_page(unsigned long addr, bool protect)
return true;
}
+#ifdef CONFIG_KFENCE
+extern bool kfence_early_init;
+static inline bool arm64_kfence_can_set_direct_map(void)
+{
+ return !kfence_early_init;
+}
+#else /* CONFIG_KFENCE */
+static inline bool arm64_kfence_can_set_direct_map(void) { return false; }
+#endif /* CONFIG_KFENCE */
+
#endif /* __ASM_KFENCE_H */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 61944c7091f0..683958616ac1 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -528,17 +528,14 @@ static int __init enable_crash_mem_map(char *arg)
early_param("crashkernel", enable_crash_mem_map);
#ifdef CONFIG_KFENCE
+bool kfence_early_init = !!CONFIG_KFENCE_SAMPLE_INTERVAL;
-static bool kfence_early_init __initdata = !!CONFIG_KFENCE_SAMPLE_INTERVAL;
-/*
- * early_param can be parsed before linear mapping
- * set up
- */
-static int __init parse_kfence_early_init(char *p)
+/* early_param() will be parsed before map_mem() below. */
+static int __init parse_kfence_early_init(char *arg)
{
int val;
- if (get_option(&p, &val))
+ if (get_option(&arg, &val))
kfence_early_init = !!val;
return 0;
}
@@ -552,22 +549,34 @@ static phys_addr_t arm64_kfence_alloc_pool(void)
return 0;
kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
- if (!kfence_pool)
+ 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;
}
-#else
-
-static phys_addr_t arm64_kfence_alloc_pool(void)
+static void arm64_kfence_map_pool(phys_addr_t kfence_pool, pgd_t *pgdp)
{
- return 0;
-}
-
-#endif
+ if (!kfence_pool)
+ return;
-phys_addr_t early_kfence_pool;
+ /* KFENCE pool needs page-level mapping. */
+ __map_memblock(pgdp, 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);
+ __kfence_pool = phys_to_virt(kfence_pool);
+}
+#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, pgd_t *pgdp) { }
+#endif /* CONFIG_KFENCE */
static void __init map_mem(pgd_t *pgdp)
{
@@ -575,6 +584,7 @@ static void __init map_mem(pgd_t *pgdp)
phys_addr_t kernel_start = __pa_symbol(_stext);
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;
@@ -588,8 +598,6 @@ static void __init map_mem(pgd_t *pgdp)
BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end));
early_kfence_pool = arm64_kfence_alloc_pool();
- if (early_kfence_pool)
- memblock_mark_nomap(early_kfence_pool, KFENCE_POOL_SIZE);
if (can_set_direct_map())
flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
@@ -656,17 +664,7 @@ static void __init map_mem(pgd_t *pgdp)
}
}
#endif
-
- /* Kfence pool needs page-level mapping */
- if (early_kfence_pool) {
- __map_memblock(pgdp, early_kfence_pool,
- early_kfence_pool + KFENCE_POOL_SIZE,
- pgprot_tagged(PAGE_KERNEL),
- NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
- memblock_clear_nomap(early_kfence_pool, KFENCE_POOL_SIZE);
- /* kfence_pool really mapped now */
- kfence_set_pool(early_kfence_pool);
- }
+ arm64_kfence_map_pool(early_kfence_pool, pgdp);
}
void mark_rodata_ro(void)
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 7ce5295cc6fb..aa8fd12cc96f 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -7,7 +7,6 @@
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/vmalloc.h>
-#include <linux/kfence.h>
#include <asm/cacheflush.h>
#include <asm/set_memory.h>
@@ -28,11 +27,10 @@ bool can_set_direct_map(void)
* mapped at page granularity, so that it is possible to
* protect/unprotect single pages.
*
- * Kfence pool requires page granularity mapping also if we init it
- * late.
+ * KFENCE pool requires page-granular mapping if initialized late.
*/
return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
- (IS_ENABLED(CONFIG_KFENCE) && !early_kfence_pool);
+ arm64_kfence_can_set_direct_map();
}
static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
diff --git a/include/linux/kfence.h b/include/linux/kfence.h
index 91cbcc98e293..726857a4b680 100644
--- a/include/linux/kfence.h
+++ b/include/linux/kfence.h
@@ -222,7 +222,6 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *sla
#else /* CONFIG_KFENCE */
-#define KFENCE_POOL_SIZE 0
static inline bool is_kfence_address(const void *addr) { return false; }
static inline void kfence_alloc_pool(void) { }
static inline void kfence_init(void) { }
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index fab087d39633..e7f22af5e710 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -818,7 +818,7 @@ void __init kfence_alloc_pool(void)
if (!kfence_sample_interval)
return;
- /* if the pool has already been initialized by arch, skip the below */
+ /* If the pool has already been initialized by arch, skip the below. */
if (__kfence_pool)
return;
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