Re: [PATCH] arm64: kprobe: make page to RO mode when allocate it

[Ard Biesheuvel]

(+ Masami)

On 15 October 2018 at 13:16, Anders Roxell <anders.roxell@xxxxxxxxxx> wrote:
> Commit 1404d6f13e47 ("arm64: dump: Add checking for writable and exectuable pages")
> has successfully identified code that leaves a page with W+X
> permissions.
>
> [    3.245140] arm64/mm: Found insecure W+X mapping at address (____ptrval____)/0xffff000000d90000
> [    3.245771] WARNING: CPU: 0 PID: 1 at ../arch/arm64/mm/dump.c:232 note_page+0x410/0x420
> [    3.246141] Modules linked in:
> [    3.246653] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.0-rc5-next-20180928-00001-ge70ae259b853-dirty #62
> [    3.247008] Hardware name: linux,dummy-virt (DT)
> [    3.247347] pstate: 80000005 (Nzcv daif -PAN -UAO)
> [    3.247623] pc : note_page+0x410/0x420
> [    3.247898] lr : note_page+0x410/0x420
> [    3.248071] sp : ffff00000804bcd0
> [    3.248254] x29: ffff00000804bcd0 x28: ffff000009274000
> [    3.248578] x27: ffff00000921a000 x26: ffff80007dfff000
> [    3.248845] x25: ffff0000093f5000 x24: ffff000009526f6a
> [    3.249109] x23: 0000000000000004 x22: ffff000000d91000
> [    3.249396] x21: ffff000000d90000 x20: 0000000000000000
> [    3.249661] x19: ffff00000804bde8 x18: 0000000000000400
> [    3.249924] x17: 0000000000000000 x16: 0000000000000000
> [    3.250271] x15: ffffffffffffffff x14: 295f5f5f5f6c6176
> [    3.250594] x13: 7274705f5f5f5f28 x12: 2073736572646461
> [    3.250941] x11: 20746120676e6970 x10: 70616d20582b5720
> [    3.251252] x9 : 6572756365736e69 x8 : 3039643030303030
> [    3.251519] x7 : 306666666678302f x6 : ffff0000095467b2
> [    3.251802] x5 : 0000000000000000 x4 : 0000000000000000
> [    3.252060] x3 : 0000000000000000 x2 : ffffffffffffffff
> [    3.252323] x1 : 4d151327adc50b00 x0 : 0000000000000000
> [    3.252664] Call trace:
> [    3.252953]  note_page+0x410/0x420
> [    3.253186]  walk_pgd+0x12c/0x238
> [    3.253417]  ptdump_check_wx+0x68/0xf8
> [    3.253637]  mark_rodata_ro+0x68/0x98
> [    3.253847]  kernel_init+0x38/0x160
> [    3.254103]  ret_from_fork+0x10/0x18
>
> Reworked to that when allocate a page it sets mode RO. Inspired by
> commit 63fef14fc98a ("kprobes/x86: Make insn buffer always ROX and use text_poke()").
>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Laura Abbott <labbott@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Co-developed-by: Arnd Bergmann <arnd@xxxxxxxx>
> Co-developed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
> ---
>  arch/arm64/kernel/probes/kprobes.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 9b65132e789a..b842e908b423 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -23,7 +23,9 @@
>  #include <linux/slab.h>
>  #include <linux/stop_machine.h>
>  #include <linux/sched/debug.h>
> +#include <linux/set_memory.h>
>  #include <linux/stringify.h>
> +#include <linux/vmalloc.h>
>  #include <asm/traps.h>
>  #include <asm/ptrace.h>
>  #include <asm/cacheflush.h>
> @@ -42,10 +44,21 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>  static void __kprobes
>  post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
>
> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> +{
> +       void *addrs[1];
> +       u32 insns[1];
> +
> +       addrs[0] = (void *)addr;
> +       insns[0] = (u32)opcode;
> +
> +       return aarch64_insn_patch_text(addrs, insns, 1);
> +}
> +
>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>  {
>         /* prepare insn slot */
> -       p->ainsn.api.insn[0] = cpu_to_le32(p->opcode);
> +       patch_text(p->ainsn.api.insn, p->opcode);
>
>         flush_icache_range((uintptr_t) (p->ainsn.api.insn),
>                            (uintptr_t) (p->ainsn.api.insn) +
> @@ -118,15 +131,15 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>         return 0;
>  }
>
> -static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> +void *alloc_insn_page(void)
>  {
> -       void *addrs[1];
> -       u32 insns[1];
> +       void *page;
>
> -       addrs[0] = (void *)addr;
> -       insns[0] = (u32)opcode;
> +       page = vmalloc_exec(PAGE_SIZE);
> +       if (page)
> +               set_memory_ro((unsigned long)page & PAGE_MASK, 1);
>
> -       return aarch64_insn_patch_text(addrs, insns, 1);
> +       return page;
>  }
>
>  /* arm kprobe: install breakpoint in text */
> --
> 2.19.1
>