Re: [RFC PATCH V2 1/2] linux-user: add a plugin API to filter syscalls

[Richard Henderson <richard.henderson@linaro.org>]

On 10/22/25 01:53, Ziyang Zhang wrote:
> @@ -165,6 +166,10 @@ qemu_plugin_vcpu_syscall(CPUState *cpu, int64_t num, uint64_t a1,
>                            uint64_t a2, uint64_t a3, uint64_t a4, uint64_t a5,
>                            uint64_t a6, uint64_t a7, uint64_t a8);
>   void qemu_plugin_vcpu_syscall_ret(CPUState *cpu, int64_t num, int64_t ret);
> +bool
> +qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
> +                         uint64_t a2, uint64_t a3, uint64_t a4, uint64_t a5,
> +                         uint64_t a6, uint64_t a7, uint64_t a8, uint64_t *ret);

The second and third lines should indented just past the ( on the first line, i.e. with 
CPUState.

> +static inline bool
> +qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
> +                                uint64_t a2, uint64_t a3, uint64_t a4,
> +                                uint64_t a5, uint64_t a6, uint64_t a7,
> +                                uint64_t a8, uint64_t *ret)

Like this.

> +typedef bool
> +(*qemu_plugin_vcpu_syscall_filter_cb_t)(qemu_plugin_id_t id,
> +                                unsigned int vcpu_index,
> +                                int64_t num, uint64_t a1, uint64_t a2,
> +                                uint64_t a3, uint64_t a4, uint64_t a5,
> +                                uint64_t a6, uint64_t a7, uint64_t a8,
> +                                uint64_t *ret);

Likewise.

> +static inline bool send_through_syscall_filters(CPUState *cpu, int num,
> +                                  abi_long arg1, abi_long arg2,
> +                                  abi_long arg3, abi_long arg4,
> +                                  abi_long arg5, abi_long arg6,
> +                                  abi_long arg7, abi_long arg8, abi_long *ret)

Do not mark inline; let the compiler decide.

> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index d78b2029fa..b8225f838f 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -14084,8 +14084,11 @@ abi_long do_syscall(CPUArchState *cpu_env, int num, abi_long arg1,
>           print_syscall(cpu_env, num, arg1, arg2, arg3, arg4, arg5, arg6);
>       }
>   
> -    ret = do_syscall1(cpu_env, num, arg1, arg2, arg3, arg4,
> -                      arg5, arg6, arg7, arg8);
> +    if (!send_through_syscall_filters(cpu, num, arg1, arg2, arg3, arg4, arg5,
> +        arg6, arg7, arg8, &ret)) {

Incorrect indent.

> +        ret = do_syscall1(cpu_env, num, arg1, arg2, arg3, arg4,
> +                        arg5, arg6, arg7, arg8);

Likewise.

> diff --git a/plugins/core.c b/plugins/core.c
> index ead09fd2f1..1b2f875fb1 100644
> --- a/plugins/core.c
> +++ b/plugins/core.c
> @@ -538,6 +538,40 @@ void qemu_plugin_vcpu_syscall_ret(CPUState *cpu, int64_t num, int64_t ret)
>       }
>   }
>   
> +/*
> + * Disable CFI checks.
> + * The callback function has been loaded from an external library so we do not
> + * have type information
> + */
> +QEMU_DISABLE_CFI
> +bool
> +qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
> +                         uint64_t a2, uint64_t a3, uint64_t a4, uint64_t a5,
> +                         uint64_t a6, uint64_t a7, uint64_t a8, uint64_t *ret)

Likewise.

> +{
> +    struct qemu_plugin_cb *cb, *next;
> +    enum qemu_plugin_event ev = QEMU_PLUGIN_EV_VCPU_SYSCALL_FILTER;
> +
> +    if (!test_bit(ev, cpu->plugin_state->event_mask)) {
> +        return false;
> +    }
> +
> +    bool filtered = false;
> +    QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
> +        qemu_plugin_vcpu_syscall_filter_cb_t func = cb->f.vcpu_syscall_filter;
> +
> +        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
> +        if (func(cb->ctx->id, cpu->cpu_index, num, a1, a2, a3, a4,
> +            a5, a6, a7, a8, ret)) {
> +            filtered = true;
> +            qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
> +            break;
> +        }
> +        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
> +    }
> +    return filtered;
> +}

The loop is better written

     QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
         bool filtered;

         qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
         filtered = cb->f.vcpu_syscall_filter(cb->ctx->id, cpu->cpu_index,
                                              num, a1, a2, a3, a4, a5,
                                              a6, a7, a8, ret);
         qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);

         if (filtered) {
             return true;
         }
     }
     return false;


r~