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

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Date:	Wed, 25 Sep 2013 20:12:17 +0530
From:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jiang Liu <liuj97@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Jiang Liu <jiang.liu@...wei.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/7] arm64: introduce interfaces to hotpatch kernel and
 module code

On 25 September 2013 20:05, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Wed, 25 Sep 2013 18:44:22 +0800
> Jiang Liu <liuj97@...il.com> wrote:
>> 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;
>
> On aarch64, are instructions always word aligned? If not, it should be
> safe for stop machine to modify non word aligned instructions, but this
> patch looks like it doesn't allow stop_machine() to do so.
Steve,

Yes, aarch64 instructions must be word-aligned, else instruction fetch
would generate Misaligned PC fault.

Thanks,
Sandeepa
>
> -- Steve
>
>> +
>> +     for (i = 0; i < cnt; i++)
>> +             tp[i] = insns[i];
>> +
>> +     flush_icache_range((uintptr_t)tp, (uintptr_t)tp + cnt * sizeof(u32));
>> +
>> +     return 0;
>> +}
>> +
>> +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 {
>> +             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;
>> +}
>
> --
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