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>

diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index 9ef6eca..defa0ff 100644 (file)
--- 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 7e9327a..27d4864 100644 (file)
--- 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)