From: Xu Kuohai <xukuohai@huawei.com>
To: Hou Tao <houtao1@huawei.com>, <bpf@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
<linux-kselftest@vger.kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
Zi Shen Lim <zlim.lnx@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
"David S . Miller" <davem@davemloft.net>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
David Ahern <dsahern@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
<hpa@zytor.com>, Shuah Khan <shuah@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
Peter Collingbourne <pcc@google.com>,
Daniel Kiss <daniel.kiss@arm.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Steven Price <steven.price@arm.com>,
Marc Zyngier <maz@kernel.org>, Mark Brown <broonie@kernel.org>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
Delyan Kratunov <delyank@fb.com>
Subject: Re: [PATCH bpf-next v2 4/6] bpf, arm64: Impelment bpf_arch_text_poke() for arm64
Date: Fri, 15 Apr 2022 11:39:38 +0800 [thread overview]
Message-ID: <d8c4f1fb-a020-9457-44e2-dc63982a9213@huawei.com> (raw)
In-Reply-To: <ba838451-1a96-2c83-9188-a994f45d7523@huawei.com>
On 4/15/2022 10:34 AM, Hou Tao wrote:
> 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@huawei.com>
>> Acked-by: Song Liu <songliubraving@fb.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 ?
Oops, I forget to check this condition. It's not safe to patch a ko
without ko unloading disabled.
For arm64, the fentry is only patched by ftrace since the nop
instruciton to be instrumented is not the first instruction, so
bpf_text_poke() fails when comparing the old instruction (pointed to by
the "old_addr") with the nop. Since the nop in fentry is reserved by
ftrace, I dont think it's reasonable to patch the nop by another
interface not provided by ftrace.
Besides, for long jumps outside the range of 128MB, a single branch
instruction is not sufficient, perhaps we could use ftrace trampoline or
some other method to support long jumps.
>> + 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;
>> +}
>
> .
next prev parent reply other threads:[~2022-04-15 3:39 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 16:22 [PATCH bpf-next v2 0/6] bpf trampoline for arm64 Xu Kuohai
2022-04-14 16:22 ` [PATCH bpf-next v2 1/6] arm64: ftrace: Add ftrace direct call support Xu Kuohai
2022-04-14 16:22 ` [PATCH bpf-next v2 2/6] ftrace: Fix deadloop caused by direct call in ftrace selftest Xu Kuohai
2022-04-20 23:24 ` Steven Rostedt
2022-04-21 3:01 ` Xu Kuohai
2022-04-14 16:22 ` [PATCH bpf-next v2 3/6] bpf: Move is_valid_bpf_tramp_flags() to the public trampoline code Xu Kuohai
2022-04-14 16:22 ` [PATCH bpf-next v2 4/6] bpf, arm64: Impelment bpf_arch_text_poke() for arm64 Xu Kuohai
2022-04-15 2:34 ` Hou Tao
2022-04-15 3:39 ` Xu Kuohai [this message]
2022-04-22 10:54 ` Jakub Sitnicki
2022-04-24 5:05 ` Xu Kuohai
2022-04-25 14:26 ` Jakub Sitnicki
2022-04-26 4:01 ` Xu Kuohai
2022-04-14 16:22 ` [PATCH bpf-next v2 5/6] bpf, arm64: bpf trampoline " Xu Kuohai
2022-04-15 17:12 ` Andrii Nakryiko
2022-04-16 1:57 ` Xu Kuohai
2022-04-20 7:43 ` Xu Kuohai
2022-04-20 11:42 ` KP Singh
2022-04-14 16:22 ` [PATCH bpf-next v2 6/6] selftests/bpf: Fix trivial typo in fentry_fexit.c Xu Kuohai
2022-04-15 2:37 ` [PATCH bpf-next v2 0/6] bpf trampoline for arm64 Hou Tao
2022-04-15 3:47 ` Xu Kuohai
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