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

From: [email-masked] (Jiang Liu)
Date: Fri, 27 Sep 2013 23:41:51 +0800

On 09/25/2013 10:35 PM, Sandeepa Prabhu wrote:
> On 25 September 2013 16:14, Jiang Liu <[email-masked]> wrote:
>> From: Jiang Liu <[email-masked]>
>>
>> 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 <[email-masked]>
>> Cc: Jiang Liu <[email-masked]>
>> ---
>>  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)
Hi Sandeepa,
	Thanks for reminder, we do need to take care of data access endian
issue here, will fix it in next version.

> 
>> +
>> +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.

After reading the attached file, I feel current implementation of
aarch64_insn_patch_text() should satisfy kprobe's requirements too.

The extra optimization of aarch64_insn_hotpatch_safe() should work
for kprobe too. For example, if we install a kprobe on a function call
instruction(BL), we need to replace "BL offset1" with "BRK" or "BL
offset2". In such cases, we could directly patch the code without
stop_machine(). Is there any special requirement that we must use
stop_machine() for kprobe here?

Thanks!
Gerry

> 
> 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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