| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <755a5b80-f916-7383-6746-3e202224dfcc@huaweicloud.com>
Date: Fri, 6 Jan 2023 09:57:49 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: Björn Töpel <bjorn@...nel.org>,
bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org
Cc: Luke Nelson <luke.r.nels@...il.com>, Xi Wang <xi.wang@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Pu Lehui <pulehui@...wei.com>
Subject: Re: [RFC PATCH RESEND bpf-next 3/4] riscv, bpf: Add
bpf_arch_text_poke support for RV64
On 2023/1/4 2:12, Björn Töpel wrote:
> Pu Lehui <pulehui@...weicloud.com> writes:
>
>> From: Pu Lehui <pulehui@...wei.com>
>>
>> Implement bpf_arch_text_poke for RV64. For call scenario,
>> ftrace framework reserve 4 nops for RV64 kernel function
>> as function entry, and use auipc+jalr instructions to call
>> kernel or module functions. However, since the auipc+jalr
>> call instructions is non-atomic operation, we need to use
>> stop-machine to make sure instruction patching in atomic
>> context. As for jump scenario, since we only jump inside
>> the trampoline, a jal instruction is sufficient.
>
> Hmm, is that really true? More below!
>
>>
>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>> ---
>> arch/riscv/net/bpf_jit.h | 5 ++
>> arch/riscv/net/bpf_jit_comp64.c | 131 +++++++++++++++++++++++++++++++-
>> 2 files changed, 134 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
>> index d926e0f7ef57..bf9802a63061 100644
>> --- a/arch/riscv/net/bpf_jit.h
>> +++ b/arch/riscv/net/bpf_jit.h
>> @@ -573,6 +573,11 @@ static inline u32 rv_fence(u8 pred, u8 succ)
>> return rv_i_insn(imm11_0, 0, 0, 0, 0xf);
>> }
>>
>> +static inline u32 rv_nop(void)
>> +{
>> + return rv_i_insn(0, 0, 0, 0, 0x13);
>> +}
>> +
>> /* RVC instrutions. */
>>
>> static inline u16 rvc_addi4spn(u8 rd, u32 imm10)
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>> index bf4721a99a09..fa8b03c52463 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -8,6 +8,8 @@
>> #include <linux/bitfield.h>
>> #include <linux/bpf.h>
>> #include <linux/filter.h>
>> +#include <linux/memory.h>
>> +#include <linux/stop_machine.h>
>> #include "bpf_jit.h"
>>
>> #define RV_REG_TCC RV_REG_A6
>> @@ -238,7 +240,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
>> if (!is_tail_call)
>> emit_mv(RV_REG_A0, RV_REG_A5, ctx);
>> emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
>> - is_tail_call ? 4 : 0, /* skip TCC init */
>> + is_tail_call ? 20 : 0, /* skip reserved nops and TCC init */
>> ctx);
>> }
>>
>> @@ -615,6 +617,127 @@ static int add_exception_handler(const struct bpf_insn *insn,
>> return 0;
>> }
>>
>> +struct text_poke_args {
>> + void *addr;
>> + const void *insns;
>> + size_t len;
>> + atomic_t cpu_count;
>> +};
>> +
>> +static int do_text_poke(void *data)
>> +{
>> + int ret = 0;
>> + struct text_poke_args *patch = data;
>> +
>> + if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
>> + ret = patch_text_nosync(patch->addr, patch->insns, patch->len);
>> + atomic_inc(&patch->cpu_count);
>> + } else {
>> + while (atomic_read(&patch->cpu_count) <= num_online_cpus())
>> + cpu_relax();
>> + smp_mb();
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int bpf_text_poke_stop_machine(void *addr, const void *insns, size_t len)
>> +{
>> + struct text_poke_args patch = {
>> + .addr = addr,
>> + .insns = insns,
>> + .len = len,
>> + .cpu_count = ATOMIC_INIT(0),
>> + };
>> +
>> + return stop_machine(do_text_poke, &patch, cpu_online_mask);
>> +}
>> +
>> +static int gen_call_or_nops(void *target, void *ip, u32 *insns)
>> +{
>> + int i, ret;
>> + s64 rvoff;
>> + struct rv_jit_context ctx;
>> +
>> + ctx.ninsns = 0;
>> + ctx.insns = (u16 *)insns;
>> +
>> + if (!target) {
>> + for (i = 0; i < 4; i++)
>> + emit(rv_nop(), &ctx);
>> + return 0;
>> + }
>> +
>> + rvoff = (s64)(target - ip);
>> + emit(rv_sd(RV_REG_SP, -8, RV_REG_RA), &ctx);
>> + ret = emit_jump_and_link(RV_REG_RA, rvoff, false, &ctx);
>> + if (ret)
>> + return ret;
>> + emit(rv_ld(RV_REG_RA, -8, RV_REG_SP), &ctx);
>> +
>> + return 0;
>> +
>> +}
>> +
>> +static int bpf_text_poke_call(void *ip, void *old_addr, void *new_addr)
>> +{
>> + int ret;
>> + u32 old_insns[4], new_insns[4];
>> +
>> + ret = gen_call_or_nops(old_addr, ip + 4, old_insns);
>> + if (ret)
>> + return ret;
>> +
>> + ret = gen_call_or_nops(new_addr, ip + 4, new_insns);
>> + if (ret)
>> + return ret;
>> +
>> + mutex_lock(&text_mutex);
>> + if (memcmp(ip, old_insns, sizeof(old_insns))) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + if (memcmp(ip, new_insns, sizeof(new_insns)))
>> + ret = bpf_text_poke_stop_machine(ip, new_insns,
>> sizeof(new_insns));
>
> I'd rather see that you added a patch_text variant to
> arch/riscv/kernel/patch.c (something like your
> bpf_text_poke_stop_machine()), and use that here. Might be other users
> of that as well -- Andy's ftrace patch maybe? :-)
>
Good idea.
>> +out:
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> +}
>> +
>> +static int bpf_text_poke_jump(void *ip, void *old_addr, void *new_addr)
>> +{
>> + int ret;
>> + u32 old_insn, new_insn;
>> +
>> + old_insn = old_addr ? rv_jal(RV_REG_ZERO, (s64)(old_addr - ip) >> 1) : rv_nop();
>> + new_insn = new_addr ? rv_jal(RV_REG_ZERO, (s64)(new_addr - ip) >> 1) : rv_nop();
>> +
>> + mutex_lock(&text_mutex);
>> + if (memcmp(ip, &old_insn, sizeof(old_insn))) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + if (memcmp(ip, &new_insn, sizeof(new_insn)))
>> + ret = patch_text_nosync(ip, &new_insn, sizeof(new_insn));
>> +out:
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> +}
>> +
>> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
>> + void *old_addr, void *new_addr)
>
> AFAIU there's nothing in the bpf_arch_text_poke() API that say that
> BPF_MOD_JUMP is jumps within the trampoline. That is one usage, but not
> the only one. In general, the jal might not have enough reach.
>
> I believe that this needs to be an auipc/jalr pair similar to
> BPF_MOD_CALL (w/o linked register).
>
The initial idea was that currently BPF_MOD_JUMP only serves for
bpf_tramp_image_put, and jal, which range is +/- 1MB, is sufficient for
the distance between im->ip_after_call and im->ip_epilogue, and try to
not use not-atomic auipc/jalr pair. But take deep consideration, this
might be extended to other uses, such as tailcall optimization. So agree
with your suggestion.
>
> And again, thanks for working on the RV trampoline!
> Björn
Powered by blists - more mailing lists