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Plugins can register a filter callback to QEMU to decide whether to intercept a syscall, process it and bypass the QEMU syscall handler. Signed-off-by: Ziyang Zhang Co-authored-by: Mingyuan Xia Reviewed-by: Pierrick Bouvier [Pierrick - move send_through_syscall_filters to linux-user/syscall.c] Link: https://lore.kernel.org/qemu-devel/20251214144620.179282-2-functioner= @sjtu.edu.cn Signed-off-by: Pierrick Bouvier --- include/qemu/plugin-event.h | 1 + include/qemu/plugin.h | 33 ++++++++++++++++++++++++--------- include/qemu/qemu-plugin.h | 32 ++++++++++++++++++++++++++++++++ linux-user/syscall.c | 24 ++++++++++++++++++++++-- plugins/api.c | 7 +++++++ plugins/core.c | 37 +++++++++++++++++++++++++++++++++++++ 6 files changed, 123 insertions(+), 11 deletions(-) diff --git a/include/qemu/plugin-event.h b/include/qemu/plugin-event.h index 1100dae2123..7f3c5927f1f 100644 --- a/include/qemu/plugin-event.h +++ b/include/qemu/plugin-event.h @@ -23,6 +23,7 @@ enum qemu_plugin_event { QEMU_PLUGIN_EV_VCPU_INTERRUPT, QEMU_PLUGIN_EV_VCPU_EXCEPTION, QEMU_PLUGIN_EV_VCPU_HOSTCALL, + QEMU_PLUGIN_EV_VCPU_SYSCALL_FILTER, QEMU_PLUGIN_EV_MAX, /* total number of plugin events we support */ }; =20 diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h index cea0a68858b..b74a7d0811b 100644 --- a/include/qemu/plugin.h +++ b/include/qemu/plugin.h @@ -55,15 +55,16 @@ void qemu_plugin_opt_parse(const char *optstr, QemuPlug= inList *head); int qemu_plugin_load_list(QemuPluginList *head, Error **errp); =20 union qemu_plugin_cb_sig { - qemu_plugin_simple_cb_t simple; - qemu_plugin_udata_cb_t udata; - qemu_plugin_vcpu_simple_cb_t vcpu_simple; - qemu_plugin_vcpu_udata_cb_t vcpu_udata; - qemu_plugin_vcpu_discon_cb_t vcpu_discon; - qemu_plugin_vcpu_tb_trans_cb_t vcpu_tb_trans; - qemu_plugin_vcpu_mem_cb_t vcpu_mem; - qemu_plugin_vcpu_syscall_cb_t vcpu_syscall; - qemu_plugin_vcpu_syscall_ret_cb_t vcpu_syscall_ret; + qemu_plugin_simple_cb_t simple; + qemu_plugin_udata_cb_t udata; + qemu_plugin_vcpu_simple_cb_t vcpu_simple; + qemu_plugin_vcpu_udata_cb_t vcpu_udata; + qemu_plugin_vcpu_discon_cb_t vcpu_discon; + qemu_plugin_vcpu_tb_trans_cb_t vcpu_tb_trans; + qemu_plugin_vcpu_mem_cb_t vcpu_mem; + qemu_plugin_vcpu_syscall_cb_t vcpu_syscall; + qemu_plugin_vcpu_syscall_ret_cb_t vcpu_syscall_ret; + qemu_plugin_vcpu_syscall_filter_cb_t vcpu_syscall_filter; void *generic; }; =20 @@ -169,6 +170,11 @@ qemu_plugin_vcpu_syscall(CPUState *cpu, int64_t num, u= int64_t a1, uint64_t a2, uint64_t a3, uint64_t a4, uint64_t a= 5, 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 *sysret); =20 void qemu_plugin_vcpu_mem_cb(CPUState *cpu, uint64_t vaddr, uint64_t value_low, @@ -280,6 +286,15 @@ static inline void qemu_plugin_vcpu_syscall_ret(CPUState *cpu, int64_t num, int64_t ret) { } =20 +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 *sysret) +{ + return false; +} + static inline void qemu_plugin_vcpu_mem_cb(CPUState *cpu, uint64_t vaddr, uint64_t value_low, uint64_t value_high, diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h index 60de4fdd3fa..84976fd67dd 100644 --- a/include/qemu/qemu-plugin.h +++ b/include/qemu/qemu-plugin.h @@ -798,6 +798,33 @@ typedef void uint64_t a3, uint64_t a4, uint64_t a5, uint64_t a6, uint64_t a7, uint64_t a8); =20 +/** + * typedef qemu_plugin_vcpu_syscall_filter_cb_t - vCPU syscall filter call= back + * function type + * @id: plugin id + * @vcpu_index: the executing vCPU + * @num: the syscall number + * @a1: the 1st syscall argument + * @a2: the 2nd syscall argument + * @a3: the 3rd syscall argument + * @a4: the 4th syscall argument + * @a5: the 5th syscall argument + * @a6: the 6th syscall argument + * @a7: the 7th syscall argument + * @a8: the 8th syscall argument + * @sysret: reference of the syscall return value, must set this if filter= ed + * + * Returns true if you want to filter this syscall (i.e. stop it being + * handled further), otherwise returns false. + */ +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 *sysret); + QEMU_PLUGIN_API void qemu_plugin_register_vcpu_syscall_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_syscall_cb_t cb= ); @@ -811,6 +838,11 @@ void qemu_plugin_register_vcpu_syscall_ret_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_syscall_ret_cb_t= cb); =20 +QEMU_PLUGIN_API +void +qemu_plugin_register_vcpu_syscall_filter_cb(qemu_plugin_id_t id, + qemu_plugin_vcpu_syscall_filte= r_cb_t cb); + =20 /** * qemu_plugin_insn_disas() - return disassembly string for instruction diff --git a/linux-user/syscall.c b/linux-user/syscall.c index b4b551ad148..3e6a56aa0f6 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -14352,6 +14352,23 @@ static void record_syscall_return(CPUState *cpu, i= nt num, abi_long ret) gdb_syscall_return(cpu, num); } =20 +static 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 *sysret) +{ + uint64_t sysret64 =3D 0; + bool filtered =3D qemu_plugin_vcpu_syscall_filter(cpu, num, arg1, arg2, + arg3, arg4, arg5, arg6, + arg7, arg8, &sysret64); + if (filtered) { + *sysret =3D sysret64; + } + return filtered; +} + abi_long do_syscall(CPUArchState *cpu_env, int num, abi_long arg1, abi_long arg2, abi_long arg3, abi_long arg4, abi_long arg5, abi_long arg6, abi_long arg7, @@ -14386,8 +14403,11 @@ abi_long do_syscall(CPUArchState *cpu_env, int num= , abi_long arg1, print_syscall(cpu_env, num, arg1, arg2, arg3, arg4, arg5, arg6); } =20 - ret =3D do_syscall1(cpu_env, num, arg1, arg2, arg3, arg4, - arg5, arg6, arg7, arg8); + if (!send_through_syscall_filters(cpu, num, arg1, arg2, arg3, arg4, ar= g5, + arg6, arg7, arg8, &ret)) { + ret =3D do_syscall1(cpu_env, num, arg1, arg2, arg3, arg4, + arg5, arg6, arg7, arg8); + } =20 if (unlikely(qemu_loglevel_mask(LOG_STRACE))) { print_syscall_ret(cpu_env, num, ret, arg1, arg2, diff --git a/plugins/api.c b/plugins/api.c index eac04cc1f6b..478d0c88890 100644 --- a/plugins/api.c +++ b/plugins/api.c @@ -208,6 +208,13 @@ qemu_plugin_register_vcpu_syscall_ret_cb(qemu_plugin_i= d_t id, plugin_register_cb(id, QEMU_PLUGIN_EV_VCPU_SYSCALL_RET, cb); } =20 +void +qemu_plugin_register_vcpu_syscall_filter_cb(qemu_plugin_id_t id, + qemu_plugin_vcpu_syscall_filte= r_cb_t cb) +{ + plugin_register_cb(id, QEMU_PLUGIN_EV_VCPU_SYSCALL_FILTER, cb); +} + /* * Plugin Queries * diff --git a/plugins/core.c b/plugins/core.c index b4b783008f7..85fabf9ec81 100644 --- a/plugins/core.c +++ b/plugins/core.c @@ -564,6 +564,43 @@ void qemu_plugin_vcpu_syscall_ret(CPUState *cpu, int64= _t num, int64_t ret) } } =20 +/* + * 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 *sysret) +{ + struct qemu_plugin_cb *cb, *next; + enum qemu_plugin_event ev =3D QEMU_PLUGIN_EV_VCPU_SYSCALL_FILTER; + bool filtered =3D false; + + if (!test_bit(ev, cpu->plugin_state->event_mask)) { + return false; + } + + qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS); + + QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) { + qemu_plugin_vcpu_syscall_filter_cb_t func =3D cb->f.vcpu_syscall_f= ilter; + + if (func(cb->ctx->id, cpu->cpu_index, num, a1, a2, a3, a4, + a5, a6, a7, a8, sysret)) { + filtered =3D true; + break; + } + } + + qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS); + + return filtered; +} + void qemu_plugin_vcpu_idle_cb(CPUState *cpu) { /* idle and resume cb may be called before init, ignore in this case */ --=20 2.47.3