Re: [RFC PATCH v2 19/20] arm64: Miscellaneous changes required for enabling livepatch

[Madhavan T. Venkataraman]

Thanks for the review.

On 7/1/22 09:16, Miroslav Benes wrote:
> Hi,
> 
> sorry for the late reply...
> 
> On Mon, 23 May 2022, madvenka@xxxxxxxxxxxxxxxxxxx wrote:
> 
>> From: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx>
>>
>> 	- Create arch/arm64/include/asm/livepatch.h and define
>> 	  klp_arch_set_pc() and klp_get_ftrace_location() which
>> 	  are required for livepatch.
>>
>> 	- Define TIF_PATCH_PENDING in arch/arm64/include/asm/thread_info.h
>> 	  for livepatch.
>>
>> 	- Check TIF_PATCH_PENDING in do_notify_resume() to patch the
>> 	  current task for livepatch.
>>
>> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
>> Signed-off-by: Madhavan T. Venkataraman <madvenka@xxxxxxxxxxxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/livepatch.h   | 42 ++++++++++++++++++++++++++++
>>  arch/arm64/include/asm/thread_info.h |  4 ++-
>>  arch/arm64/kernel/signal.c           |  4 +++
>>  3 files changed, 49 insertions(+), 1 deletion(-)
>>  create mode 100644 arch/arm64/include/asm/livepatch.h
>>
>> diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h
>> new file mode 100644
>> index 000000000000..72d7cd86f158
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/livepatch.h
>> @@ -0,0 +1,42 @@
>> +/* SPDX-License-Identifier: GPL-2.0
>> + *
>> + * livepatch.h - arm64-specific Kernel Live Patching Core
>> + */
>> +#ifndef _ASM_ARM64_LIVEPATCH_H
>> +#define _ASM_ARM64_LIVEPATCH_H
>> +
>> +#include <linux/ftrace.h>
>> +
>> +static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>> +{
>> +	struct pt_regs *regs = ftrace_get_regs(fregs);
>> +
>> +	regs->pc = ip;
>> +}
> 
> kernel/livepatch/ does not use klp_arch_set_pc() anymore. It was replaced 
> by ftrace_instruction_pointer_set() and 
> CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS.
> 

OK. I will address this in the next version.
Thanks for pointing it out.

>> +/*
>> + * klp_get_ftrace_location is expected to return the address of the BL to the
>> + * relevant ftrace handler in the callsite. The location of this can vary based
>> + * on several compilation options.
>> + * CONFIG_DYNAMIC_FTRACE_WITH_REGS
>> + *	- Inserts 2 nops on function entry the second of which is the BL
>> + *	  referenced above. (See ftrace_init_nop() for the callsite sequence)
>> + *	  (this is required by livepatch and must be selected)
>> + * CONFIG_ARM64_BTI_KERNEL:
>> + *	- Inserts a hint #0x22 on function entry if the function is called
>> + *	  indirectly (to satisfy BTI requirements), which is inserted before
>> + *	  the two nops from above.
>> + */
>> +#define klp_get_ftrace_location klp_get_ftrace_location
>> +static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
>> +{
>> +	unsigned long addr = faddr + AARCH64_INSN_SIZE;
>> +
>> +#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
>> +	addr = ftrace_location_range(addr, addr + AARCH64_INSN_SIZE);
>> +#endif
>> +
>> +	return addr;
>> +}
> 
> This is not needed either. peterz improved the ftrace code and livepatch 
> now uses ftrace_location() which gives the proper location directly.
> 

OK. I will remove this in the next version.

>> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
>> index e1317b7c4525..a1d8999dbdcc 100644
>> --- a/arch/arm64/include/asm/thread_info.h
>> +++ b/arch/arm64/include/asm/thread_info.h
>> @@ -68,6 +68,7 @@ int arch_dup_task_struct(struct task_struct *dst,
>>  #define TIF_UPROBE		4	/* uprobe breakpoint or singlestep */
>>  #define TIF_MTE_ASYNC_FAULT	5	/* MTE Asynchronous Tag Check Fault */
>>  #define TIF_NOTIFY_SIGNAL	6	/* signal notifications exist */
>> +#define TIF_PATCH_PENDING	7	/* pending live patching update */
>>  #define TIF_SYSCALL_TRACE	8	/* syscall trace active */
>>  #define TIF_SYSCALL_AUDIT	9	/* syscall auditing */
>>  #define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */
>> @@ -98,11 +99,12 @@ int arch_dup_task_struct(struct task_struct *dst,
>>  #define _TIF_SVE		(1 << TIF_SVE)
>>  #define _TIF_MTE_ASYNC_FAULT	(1 << TIF_MTE_ASYNC_FAULT)
>>  #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
>> +#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)
>>  
>>  #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
>>  				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
>>  				 _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \
>> -				 _TIF_NOTIFY_SIGNAL)
>> +				 _TIF_NOTIFY_SIGNAL | _TIF_PATCH_PENDING)
>>  
>>  #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
>>  				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
>> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
>> index 4a4122ef6f39..cbec9597349f 100644
>> --- a/arch/arm64/kernel/signal.c
>> +++ b/arch/arm64/kernel/signal.c
>> @@ -17,6 +17,7 @@
>>  #include <linux/sizes.h>
>>  #include <linux/string.h>
>>  #include <linux/resume_user_mode.h>
>> +#include <linux/livepatch.h>
>>  #include <linux/ratelimit.h>
>>  #include <linux/syscalls.h>
>>  
>> @@ -938,6 +939,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
>>  					       (void __user *)NULL, current);
>>  			}
>>  
>> +			if (thread_flags & _TIF_PATCH_PENDING)
>> +				klp_update_patch_state(current);
>> +
>>  			if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
>>  				do_signal(regs);
> 
> The rest should be fine.
> 

Thanks!

Madhavan