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@xxxxxxxxxx>
> Acked-by: Song Liu <songliubraving@xxxxxx>
> ---
> 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;
> +}
