On 2023/3/13 21:00, Marco Elver wrote:
On Mon, 13 Mar 2023 at 12:57, Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx> 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@liebao ]# cat /proc/meminfo
MemTotal: 999484 kB
After:
[root@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@xxxxxxx>
Signed-off-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
---
arch/arm64/mm/mmu.c | 42 ++++++++++++++++++++++++++++++++++++++++++
arch/arm64/mm/pageattr.c | 8 ++++++--
include/linux/kfence.h | 10 ++++++++++
mm/kfence/core.c | 9 +++++++++
4 files changed, 67 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 6f9d889..ca5c932 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -24,6 +24,7 @@
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/set_memory.h>
+#include <linux/kfence.h>
#include <asm/barrier.h>
#include <asm/cputype.h>
@@ -525,6 +526,31 @@ static int __init enable_crash_mem_map(char *arg)
}
early_param("crashkernel", enable_crash_mem_map);
+#ifdef CONFIG_KFENCE
+
+static phys_addr_t arm64_kfence_alloc_pool(void)
+{
+ phys_addr_t kfence_pool;
+
+ if (!kfence_sample_interval)
+ return 0;
+
+ kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+ if (!kfence_pool)
+ pr_err("failed to allocate kfence pool\n");
+
+ return kfence_pool;
+}
+
+#else
+
+static phys_addr_t arm64_kfence_alloc_pool(void)
+{
+ return 0;
+}
+
+#endif
+
static void __init map_mem(pgd_t *pgdp)
{
static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
@@ -532,6 +558,7 @@ static void __init map_mem(pgd_t *pgdp)
phys_addr_t kernel_end = __pa_symbol(__init_begin);
phys_addr_t start, end;
int flags = NO_EXEC_MAPPINGS;
+ phys_addr_t kfence_pool;
u64 i;
/*
@@ -564,6 +591,10 @@ static void __init map_mem(pgd_t *pgdp)
}
#endif
+ kfence_pool = arm64_kfence_alloc_pool();
+ if (kfence_pool)
+ memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
+
/* map all the memory banks */
for_each_mem_range(i, &start, &end) {
if (start >= end)
@@ -608,6 +639,17 @@ static void __init map_mem(pgd_t *pgdp)
}
}
#endif
+
+ /* Kfence pool needs page-level mapping */
+ if (kfence_pool) {
+ __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 really mapped now */
+ kfence_set_pool(kfence_pool);
+ }
}
void mark_rodata_ro(void)
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 79dd201..25e4a983 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -7,6 +7,7 @@
#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>
@@ -22,12 +23,15 @@ bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED
bool can_set_direct_map(void)
{
/*
- * rodata_full, DEBUG_PAGEALLOC and KFENCE require linear map to be
+ * rodata_full and DEBUG_PAGEALLOC require linear map to be
* 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.
*/
return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
- IS_ENABLED(CONFIG_KFENCE);
+ (IS_ENABLED(CONFIG_KFENCE) && !kfence_sample_interval);
If you're struggling with kfence_sample_interval not existing if
!CONFIG_KFENCE, this is one of the occasions where it'd be perfectly
fine to write:
bool can_set_direct_map(void) {
#ifdef CONFIG_KFENCE
/* ... your comment here ...*/
if (!kfence_sample_interval)
return true;
}
#endif
return .........
}
}
The can_set_direct_map() could be called anytime, eg, memory add,
vmalloc, and this will make different state of can_set_direct_map()
if kfence is re-enabled, I think that we need a new value to check
whether or not the early kfence_pool is initialized.
