[PATCH v1 2/7] arm64: introduce interfaces to hotpatch kernel and module code

[Sandeepa Prabhu]

On 25 September 2013 16:14, Jiang Liu <liuj97 at gmail.com> wrote:
> From: Jiang Liu <jiang.liu at huawei.com>
>
> Introduce aarch64_insn_patch_text() and __aarch64_insn_patch_text()
> to patch kernel and module code.
>
> Function aarch64_insn_patch_text() is a heavy version which may use
> stop_machine() to serialize all online CPUs, and function
> __aarch64_insn_patch_text() is light version without explicitly
> serialization.
Hi Jiang,

I have written kprobes support for aarch64, and need both the
functionality (lightweight and stop_machine() versions).
I would like to rebase these API in kprobes, however slight changes
would require in case of stop_machine version, which I explained
below.
[Though kprobes cannot share Instruction encode support of jump labels
as, decoding & simulation quite different for kprobes/uprobes and
based around single stepping]

>
> Signed-off-by: Jiang Liu <jiang.liu at huawei.com>
> Cc: Jiang Liu <liuj97 at gmail.com>
> ---
>  arch/arm64/include/asm/insn.h |  2 ++
>  arch/arm64/kernel/insn.c      | 64 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
>
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index e7d1bc8..0ea7193 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -49,5 +49,7 @@ __AARCH64_INSN_FUNCS(nop,     0xFFFFFFFF, 0xD503201F)
>  enum aarch64_insn_class aarch64_get_insn_class(u32 insn);
>
>  bool aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn);
> +int aarch64_insn_patch_text(void *addr, u32 *insns, int cnt);
> +int __aarch64_insn_patch_text(void *addr, u32 *insns, int cnt);
>
>  #endif /* _ASM_ARM64_INSN_H */
> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
> index 8541c3a..50facfc 100644
> --- a/arch/arm64/kernel/insn.c
> +++ b/arch/arm64/kernel/insn.c
> @@ -15,6 +15,8 @@
>   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
>  #include <linux/kernel.h>
> +#include <linux/stop_machine.h>
> +#include <asm/cacheflush.h>
>  #include <asm/insn.h>
>
>  static int aarch64_insn_cls[] = {
> @@ -69,3 +71,65 @@ bool __kprobes aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn)
>         return __aarch64_insn_hotpatch_safe(old_insn) &&
>                __aarch64_insn_hotpatch_safe(new_insn);
>  }
> +
> +struct aarch64_insn_patch {
> +       void    *text_addr;
> +       u32     *new_insns;
> +       int     insn_cnt;
> +};
> +
> +int __kprobes __aarch64_insn_patch_text(void *addr, u32 *insns, int cnt)
> +{
> +       int i;
> +       u32 *tp = addr;
> +
> +       /* instructions must be word aligned */
> +       if (cnt <= 0 || ((uintptr_t)addr & 0x3))
> +               return -EINVAL;
> +
> +       for (i = 0; i < cnt; i++)
> +               tp[i] = insns[i];
> +
> +       flush_icache_range((uintptr_t)tp, (uintptr_t)tp + cnt * sizeof(u32));
> +
> +       return 0;
> +}
Looks fine, but do you need to check for CPU big endian mode here? (I
think swab32() needed if EL1 is in big-endian mode)

> +
> +static int __kprobes aarch64_insn_patch_text_cb(void *arg)
> +{
> +       struct aarch64_insn_patch *pp = arg;
> +
> +       return __aarch64_insn_patch_text(pp->text_addr, pp->new_insns,
> +                                        pp->insn_cnt);
> +}
> +
> +int __kprobes aarch64_insn_patch_text(void *addr, u32 *insns, int cnt)
> +{
> +       int ret;
> +       bool safe = false;
> +
> +       /* instructions must be word aligned */
> +       if (cnt <= 0 || ((uintptr_t)addr & 0x3))
> +               return -EINVAL;
> +
> +       if (cnt == 1)
> +               safe = aarch64_insn_hotpatch_safe(*(u32 *)addr, insns[0]);
> +
> +       if (safe) {
> +               ret = __aarch64_insn_patch_text(addr, insns, cnt);
> +       } else {

Can you move the code below this into separate API that just apply
patch with stop_machine? And then a wrapper function for jump label
specific handling that checks for aarch64_insn_hotpatch_safe() ?
Also, it will be good to move the patching code out of insn.c to
patch.c (refer to arch/arm/kernel/patch.c).

Please refer to attached file (my current implementation) to make
sense of exactly what kprobes would need (ignore the big-endian part
for now). I think splitting the code should be straight-forward and we
can avoid two different implementations. Please let me know if this
can be done, I will rebase my patches above your next version.

Thanks,
Sandeepa
> +               struct aarch64_insn_patch patch = {
> +                       .text_addr = addr,
> +                       .new_insns = insns,
> +                       .insn_cnt = cnt,
> +               };
> +
> +               /*
> +                * Execute __aarch64_insn_patch_text() on every online CPU,
> +                * which ensure serialization among all online CPUs.
> +                */
> +               ret = stop_machine(aarch64_insn_patch_text_cb, &patch, NULL);
> +       }
> +
> +       return ret;
> +}
> --
> 1.8.1.2
>
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