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From: Palmer Dabbelt <palmerdabbelt@google.com>
To: guoren@kernel.org
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	mhiramat@kernel.org, oleg@redhat.com,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	anup@brainfault.org, linux-csky@vger.kernel.org,
	greentime.hu@sifive.com, zong.li@sifive.com, guoren@kernel.org,
	me@packi.ch, Bjorn Topel <bjorn.topel@gmail.com>,
	guoren@linux.alibaba.com
Subject: Re: [PATCH v3 3/7] riscv: Fixup kprobes handler couldn't change pc
Date: Fri, 14 Aug 2020 15:36:06 -0700 (PDT)	[thread overview]
Message-ID: <mhng-296dd63e-71de-4d30-acfb-df374d12388d@palmerdabbelt-glaptop1> (raw)
In-Reply-To: <1594683562-68149-4-git-send-email-guoren@kernel.org>

On Mon, 13 Jul 2020 16:39:18 PDT (-0700), guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
>
> The "Changing Execution Path" section in the Documentation/kprobes.txt
> said:
>
> Since kprobes can probe into a running kernel code, it can change the
> register set, including instruction pointer.
>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Palmer Dabbelt <palmerdabbelt@google.com>
> ---
>  arch/riscv/kernel/mcount-dyn.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> index 35a6ed7..4b58b54 100644
> --- a/arch/riscv/kernel/mcount-dyn.S
> +++ b/arch/riscv/kernel/mcount-dyn.S
> @@ -123,6 +123,7 @@ ENDPROC(ftrace_caller)
>  	sd	ra, (PT_SIZE_ON_STACK+8)(sp)
>  	addi	s0, sp, (PT_SIZE_ON_STACK+16)
>
> +	sd ra,  PT_EPC(sp)
>  	sd x1,  PT_RA(sp)
>  	sd x2,  PT_SP(sp)
>  	sd x3,  PT_GP(sp)

So that's definately not going to be EPC any more.  I'm not sure that field is
sanely named, though, as it's really just the PC when it comes to other ptrace
stuff.

> @@ -157,6 +158,7 @@ ENDPROC(ftrace_caller)
>  	.endm
>
>  	.macro RESTORE_ALL
> +	ld ra,  PT_EPC(sp)
>  	ld x1,  PT_RA(sp)

x1 is ra, so loading it twice doesn't seem reasonable.

>  	ld x2,  PT_SP(sp)
>  	ld x3,  PT_GP(sp)
> @@ -190,7 +192,6 @@ ENDPROC(ftrace_caller)
>  	ld x31, PT_T6(sp)
>
>  	ld	s0, (PT_SIZE_ON_STACK)(sp)
> -	ld	ra, (PT_SIZE_ON_STACK+8)(sp)
>  	addi	sp, sp, (PT_SIZE_ON_STACK+16)
>  	.endm

If you're dropping the load you should drop the store above as well.  In
general this seems kind of mixed up, both before and after this patch.

  parent reply	other threads:[~2020-08-14 22:36 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-13 23:39 [PATCH v3 0/7] riscv: Add k/uprobe supported guoren
2020-07-13 23:39 ` [PATCH v3 1/7] RISC-V: Implement ptrace regs and stack API guoren
2020-07-14 11:25   ` Masami Hiramatsu
2020-07-13 23:39 ` [PATCH v3 2/7] riscv: Fixup compile error BUILD_BUG_ON failed guoren
2020-07-13 23:39 ` [PATCH v3 3/7] riscv: Fixup kprobes handler couldn't change pc guoren
2020-07-14 11:32   ` Masami Hiramatsu
2020-08-14 22:36   ` Palmer Dabbelt [this message]
2020-08-17 12:47     ` Guo Ren
2020-07-13 23:39 ` [PATCH v3 4/7] riscv: Add kprobes supported guoren
2020-08-14 22:36   ` Palmer Dabbelt
2020-08-17 13:48     ` Guo Ren
2020-07-13 23:39 ` [PATCH v3 5/7] riscv: Add uprobes supported guoren
2020-07-13 23:39 ` [PATCH v3 6/7] riscv: Add KPROBES_ON_FTRACE supported guoren
2020-07-14 11:37   ` Masami Hiramatsu
2020-07-14 16:24     ` Guo Ren
2020-07-21 13:27       ` Masami Hiramatsu
2020-07-22  8:39         ` Guo Ren
2020-07-23 15:55           ` Masami Hiramatsu
2020-07-22 13:31         ` Guo Ren
2020-07-23 16:11           ` Masami Hiramatsu
2020-07-13 23:39 ` [PATCH v3 7/7] riscv: Add support for function error injection guoren
2020-07-14 11:43   ` Masami Hiramatsu
2020-07-14 11:23 ` [PATCH v3 0/7] riscv: Add k/uprobe supported Masami Hiramatsu
2020-07-15  6:45   ` Guo Ren

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