arm64: use fixmap for text patching

When kernel text is marked as read only, it cannot be modified directly.
Use a fixmap to modify the text instead in a similar manner to
x86 and arm.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

2 files changed, 47 insertions, 1 deletions

diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index 9ef6eca905ca..defa0ff98250 100644
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -49,6 +49,7 @@ enum fixed_addresses {
 
         FIX_BTMAP_END = __end_of_permanent_fixed_addresses,
         FIX_BTMAP_BEGIN = FIX_BTMAP_END + TOTAL_FIX_BTMAPS - 1,
+        FIX_TEXT_POKE0,
         __end_of_fixed_addresses
 };
 
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index 7e9327a0986d..27d4864577e5 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -17,14 +17,19 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <linux/bitops.h>
+#include <linux/bug.h>
 #include <linux/compiler.h>
 #include <linux/kernel.h>
+#include <linux/mm.h>
 #include <linux/smp.h>
+#include <linux/spinlock.h>
 #include <linux/stop_machine.h>
+#include <linux/types.h>
 #include <linux/uaccess.h>
 
 #include <asm/cacheflush.h>
 #include <asm/debug-monitors.h>
+#include <asm/fixmap.h>
 #include <asm/insn.h>
 
 #define AARCH64_INSN_SF_BIT     BIT(31)
@@ -72,6 +77,29 @@ bool __kprobes aarch64_insn_is_nop(u32 insn)
         }
 }
 
+static DEFINE_SPINLOCK(patch_lock);
+
+static void __kprobes *patch_map(void *addr, int fixmap)
+{
+        unsigned long uintaddr = (uintptr_t) addr;
+        bool module = !core_kernel_text(uintaddr);
+        struct page *page;
+
+        if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
+                page = vmalloc_to_page(addr);
+        else
+                page = virt_to_page(addr);
+
+        BUG_ON(!page);
+        set_fixmap(fixmap, page_to_phys(page));
+
+        return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
+}
+
+static void __kprobes patch_unmap(int fixmap)
+{
+        clear_fixmap(fixmap);
+}
 /*
  * In ARMv8-A, A64 instructions have a fixed length of 32 bits and are always
  * little-endian.
@@ -88,10 +116,27 @@ int __kprobes aarch64_insn_read(void *addr, u32 *insnp)
         return ret;
 }
 
+static int __kprobes __aarch64_insn_write(void *addr, u32 insn)
+{
+        void *waddr = addr;
+        unsigned long flags = 0;
+        int ret;
+
+        spin_lock_irqsave(&patch_lock, flags);
+        waddr = patch_map(addr, FIX_TEXT_POKE0);
+
+        ret = probe_kernel_write(waddr, &insn, AARCH64_INSN_SIZE);
+
+        patch_unmap(FIX_TEXT_POKE0);
+        spin_unlock_irqrestore(&patch_lock, flags);
+
+        return ret;
+}
+
 int __kprobes aarch64_insn_write(void *addr, u32 insn)
 {
         insn = cpu_to_le32(insn);
-        return probe_kernel_write(addr, &insn, AARCH64_INSN_SIZE);
+        return __aarch64_insn_write(addr, insn);
 }
 
 static bool __kprobes __aarch64_insn_hotpatch_safe(u32 insn)