netdev - Re: [PATCH bpf-next v2 4/6] bpf, arm64: Impelment bpf_arch_text

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Message-ID: <ba838451-1a96-2c83-9188-a994f45d7523@huawei.com>
Date:   Fri, 15 Apr 2022 10:34:47 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Xu Kuohai <xukuohai@...wei.com>, <bpf@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <hpa@...or.com>, Shuah Khan <shuah@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Daniel Kiss <daniel.kiss@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Steven Price <steven.price@....com>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Delyan Kratunov <delyank@...com>
Subject: Re: [PATCH bpf-next v2 4/6] bpf, arm64: Impelment
 bpf_arch_text_poke() for arm64

Hi,

On 4/15/2022 12:22 AM, Xu Kuohai wrote:
> Impelment bpf_arch_text_poke() for arm64, so bpf trampoline code can use
> it to replace nop with jump, or replace jump with nop.
>
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> Acked-by: Song Liu <songliubraving@...com>
> ---
>  arch/arm64/net/bpf_jit_comp.c | 52 +++++++++++++++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
>
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 8ab4035dea27..1a1c3ea75ee2 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/bitfield.h>
>  #include <linux/bpf.h>
> +#include <linux/memory.h>
>  #include <linux/filter.h>
>  #include <linux/printk.h>
>  #include <linux/slab.h>
> @@ -18,6 +19,7 @@
>  #include <asm/cacheflush.h>
>  #include <asm/debug-monitors.h>
>  #include <asm/insn.h>
> +#include <asm/patching.h>
>  #include <asm/set_memory.h>
>  
>  #include "bpf_jit.h"
> @@ -1529,3 +1531,53 @@ void bpf_jit_free_exec(void *addr)
>  {
>  	return vfree(addr);
>  }
> +
> +static int gen_branch_or_nop(enum aarch64_insn_branch_type type, void *ip,
> +			     void *addr, u32 *insn)
> +{
> +	if (!addr)
> +		*insn = aarch64_insn_gen_nop();
> +	else
> +		*insn = aarch64_insn_gen_branch_imm((unsigned long)ip,
> +						    (unsigned long)addr,
> +						    type);
> +
> +	return *insn != AARCH64_BREAK_FAULT ? 0 : -EFAULT;
> +}
> +
> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
> +		       void *old_addr, void *new_addr)
> +{
> +	int ret;
> +	u32 old_insn;
> +	u32 new_insn;
> +	u32 replaced;
> +	enum aarch64_insn_branch_type branch_type;
> +
In bpf_arch_text_poke() of x86, it disables the poking of kernel module, can you
explain why it is OK to do so in arm64 ? Because there is no test cases for
fentry on linux kernel module, could you please add some tests for it ?
> +	if (poke_type == BPF_MOD_CALL)
> +		branch_type = AARCH64_INSN_BRANCH_LINK;
> +	else
> +		branch_type = AARCH64_INSN_BRANCH_NOLINK;
> +
> +	if (gen_branch_or_nop(branch_type, ip, old_addr, &old_insn) < 0)
> +		return -EFAULT;
> +
> +	if (gen_branch_or_nop(branch_type, ip, new_addr, &new_insn) < 0)
> +		return -EFAULT;
> +
> +	mutex_lock(&text_mutex);
> +	if (aarch64_insn_read(ip, &replaced)) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	if (replaced != old_insn) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	ret =  aarch64_insn_patch_text_nosync((void *)ip, new_insn);
> +out:
> +	mutex_unlock(&text_mutex);
> +	return ret;
> +}