Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support

From: Patrick Staehlin <me@packi.ch>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Palmer Dabbelt <palmer@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alan Kao <alankao@andestech.com>, Zong Li <zong@andestech.com>,
	Ingo Molnar <mingo@kernel.org>, Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	zhong jiang <zhongjiang@huawei.com>,
	Anders Roxell <anders.roxell@linaro.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Jim Wilson <jimw@sifive.com>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Souptick Joarder <jrdr.linux@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [RFC/RFT 2/2] RISC-V: kprobes/kretprobe support
Date: Wed, 14 Nov 2018 22:10:52 +0100	[thread overview]
Message-ID: <05082ba4-33d6-a95c-e049-78791dafc009@packi.ch> (raw)
In-Reply-To: <20181114074951.0902699286fdf8652f2878a4@kernel.org>

On 14.11.18 16:49, Masami Hiramatsu wrote:
> On Wed, 14 Nov 2018 00:37:30 -0800
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
>>> +
>>> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
>>> +{
>>> +	if (is_compressed_insn(opcode))
>>> +		*(u16 *)addr = cpu_to_le16(opcode);
>>> +	else
>>> +		*addr = cpu_to_le32(opcode);
>>> +
> 
> BTW, don't RISC-V need any i-cache flush and per-core serialization
> for patching the text area? (and no text_mutex protection?)

Yes, we should probably call flush_icache_all. This code works on
QEMU/virt but I guess on real hardware you may run into problems,
especially when disarming the kprobe. I'll have a look at the arm64 code
again to see what's missing.

> 
>>> diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
>>> new file mode 100644
>>> index 000000000000..c7ceda9556a3
>>> --- /dev/null
>>> +++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
>>> @@ -0,0 +1,91 @@
>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>> +
>>> +#include <linux/linkage.h>
>>> +
>>> +#include <asm/asm.h>
>>> +#include <asm/asm-offsets.h>
>>> +
>>> +	.text
>>> +	.altmacro
>>> +
>>> +	.macro save_all_base_regs
>>> +	REG_S x1,  PT_RA(sp)
>>> +	REG_S x3,  PT_GP(sp)
>>> +	REG_S x4,  PT_TP(sp)
>>> +	REG_S x5,  PT_T0(sp)
>>> +	REG_S x6,  PT_T1(sp)
>>> +	REG_S x7,  PT_T2(sp)
>>> +	REG_S x8,  PT_S0(sp)
>>> +	REG_S x9,  PT_S1(sp)
>>> +	REG_S x10, PT_A0(sp)
>>> +	REG_S x11, PT_A1(sp)
>>> +	REG_S x12, PT_A2(sp)
>>> +	REG_S x13, PT_A3(sp)
>>> +	REG_S x14, PT_A4(sp)
>>> +	REG_S x15, PT_A5(sp)
>>> +	REG_S x16, PT_A6(sp)
>>> +	REG_S x17, PT_A7(sp)
>>> +	REG_S x18, PT_S2(sp)
>>> +	REG_S x19, PT_S3(sp)
>>> +	REG_S x20, PT_S4(sp)
>>> +	REG_S x21, PT_S5(sp)
>>> +	REG_S x22, PT_S6(sp)
>>> +	REG_S x23, PT_S7(sp)
>>> +	REG_S x24, PT_S8(sp)
>>> +	REG_S x25, PT_S9(sp)
>>> +	REG_S x26, PT_S10(sp)
>>> +	REG_S x27, PT_S11(sp)
>>> +	REG_S x28, PT_T3(sp)
>>> +	REG_S x29, PT_T4(sp)
>>> +	REG_S x30, PT_T5(sp)
>>> +	REG_S x31, PT_T6(sp)
>>> +	.endm
>>> +
>>> +	.macro restore_all_base_regs
>>> +	REG_L x3,  PT_GP(sp)
>>> +	REG_L x4,  PT_TP(sp)
>>> +	REG_L x5,  PT_T0(sp)
>>> +	REG_L x6,  PT_T1(sp)
>>> +	REG_L x7,  PT_T2(sp)
>>> +	REG_L x8,  PT_S0(sp)
>>> +	REG_L x9,  PT_S1(sp)
>>> +	REG_L x10, PT_A0(sp)
>>> +	REG_L x11, PT_A1(sp)
>>> +	REG_L x12, PT_A2(sp)
>>> +	REG_L x13, PT_A3(sp)
>>> +	REG_L x14, PT_A4(sp)
>>> +	REG_L x15, PT_A5(sp)
>>> +	REG_L x16, PT_A6(sp)
>>> +	REG_L x17, PT_A7(sp)
>>> +	REG_L x18, PT_S2(sp)
>>> +	REG_L x19, PT_S3(sp)
>>> +	REG_L x20, PT_S4(sp)
>>> +	REG_L x21, PT_S5(sp)
>>> +	REG_L x22, PT_S6(sp)
>>> +	REG_L x23, PT_S7(sp)
>>> +	REG_L x24, PT_S8(sp)
>>> +	REG_L x25, PT_S9(sp)
>>> +	REG_L x26, PT_S10(sp)
>>> +	REG_L x27, PT_S11(sp)
>>> +	REG_L x28, PT_T3(sp)
>>> +	REG_L x29, PT_T4(sp)
>>> +	REG_L x30, PT_T5(sp)
>>> +	REG_L x31, PT_T6(sp)
>>> +	.endm
> 
> 
> It seems thses macros can be (partially?) shared with entry.S

Yes, I wanted to avoid somebody changing the shared code and breaking
random things. But that's what reviews are for. I'll think of something
for v2.