@@ -11,6 +11,8 @@
#include <linux/cpuhotplug.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
+#include <linux/sched/task.h>
+#include <linux/random.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
@@ -39,6 +41,37 @@ int raw_patch_instruction(unsigned int *addr, unsigned int instr)
}
#ifdef CONFIG_STRICT_KERNEL_RWX
+
+static struct mm_struct *patching_mm __ro_after_init;
+static unsigned long patching_addr __ro_after_init;
+
+void __init poking_init(void)
+{
+ spinlock_t *ptl; /* for protecting pte table */
+ pte_t *ptep;
+
+ /*
+ * Some parts of the kernel (static keys for example) depend on
+ * successful code patching. Code patching under STRICT_KERNEL_RWX
+ * requires this setup - otherwise we cannot patch at all. We use
+ * BUG_ON() here and later since an early failure is preferred to
+ * buggy behavior and/or strange crashes later.
+ */
+ patching_mm = copy_init_mm();
+ BUG_ON(!patching_mm);
+
+ /*
+ * In hash we cannot go above DEFAULT_MAP_WINDOW easily.
+ * XXX: Do we want additional bits of entropy for radix?
+ */
+ patching_addr = (get_random_long() & PAGE_MASK) %
+ (DEFAULT_MAP_WINDOW - PAGE_SIZE);
+
+ ptep = get_locked_pte(patching_mm, patching_addr, &ptl);
+ BUG_ON(!ptep);
+ pte_unmap_unlock(ptep, ptl);
+}
+
static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
static int text_area_cpu_up(unsigned int cpu)
When code patching a STRICT_KERNEL_RWX kernel the page containing the address to be patched is temporarily mapped with permissive memory protections. Currently, a per-cpu vmalloc patch area is used for this purpose. While the patch area is per-cpu, the temporary page mapping is inserted into the kernel page tables for the duration of the patching. The mapping is exposed to CPUs other than the patching CPU - this is undesirable from a hardening perspective. Use the `poking_init` init hook to prepare a temporary mm and patching address. Initialize the temporary mm by copying the init mm. Choose a randomized patching address inside the temporary mm userspace address portion. The next patch uses the temporary mm and patching address for code patching. Based on x86 implementation: commit 4fc19708b165 ("x86/alternatives: Initialize temporary mm for patching") Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> --- arch/powerpc/lib/code-patching.c | 33 ++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+)