| Message ID | 20220815190303.2061559-2-peter.maydell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Allow semihosting from user mode | expand |
On 15/8/22 21:02, Peter Maydell wrote: > Currently our semihosting implementations generally prohibit use of > semihosting calls in system emulation from the guest userspace. This > is a very long standing behaviour justified originally "to provide > some semblance of security" (since code with access to the > semihosting ABI can do things like read and write arbitrary files on > the host system). However, it is sometimes useful to be able to run > trusted guest code which performs semihosting calls from guest > userspace, notably for test code. Add a command line suboption to > the existing semihosting-config option group so that you can > explicitly opt in to semihosting from guest userspace with > -semihosting-config userspace=on > > (There is no equivalent option for the user-mode emulator, because > there by definition all code runs in userspace and has access to > semihosting already.) > > This commit adds the infrastructure for the command line option and > adds a bool 'is_user' parameter to the function > semihosting_userspace_enabled() that target code can use to check > whether it should be permitting the semihosting call for userspace. > It mechanically makes all the callsites pass 'false', so they > continue checking "is semihosting enabled in general". Subsequent > commits will make each target that implements semihosting honour the > userspace=on option by passing the correct value and removing > whatever "don't do this for userspace" checking they were doing by > hand. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> > --- > include/semihosting/semihost.h | 10 ++++++++-- > semihosting/config.c | 10 ++++++++-- > softmmu/vl.c | 2 +- > stubs/semihost.c | 2 +- > target/arm/translate-a64.c | 2 +- > target/arm/translate.c | 6 +++--- > target/m68k/op_helper.c | 2 +- > target/nios2/translate.c | 2 +- > target/xtensa/translate.c | 6 +++--- > qemu-options.hx | 11 +++++++++-- > 10 files changed, 36 insertions(+), 17 deletions(-) > > diff --git a/include/semihosting/semihost.h b/include/semihosting/semihost.h > index 93a3c21b44d..efd2efa25ae 100644 > --- a/include/semihosting/semihost.h > +++ b/include/semihosting/semihost.h > @@ -27,7 +27,7 @@ typedef enum SemihostingTarget { > } SemihostingTarget; > > #ifdef CONFIG_USER_ONLY > -static inline bool semihosting_enabled(void) > +static inline bool semihosting_enabled(bool is_user) > { > return true; > } > @@ -52,7 +52,13 @@ static inline const char *semihosting_get_cmdline(void) > return NULL; > } > #else /* !CONFIG_USER_ONLY */ > -bool semihosting_enabled(void); > +/** > + * semihosting_enabled: > + * @is_user: true if guest code is in usermode (i.e. not privileged) > + * > + * Return true if guest code is allowed to make semihosting calls. > + */ > +bool semihosting_enabled(bool is_user); Per the description, possibly rename as semihosting_allowed(). Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Peter Maydell <peter.maydell@linaro.org> writes: > Currently our semihosting implementations generally prohibit use of > semihosting calls in system emulation from the guest userspace. This > is a very long standing behaviour justified originally "to provide > some semblance of security" (since code with access to the > semihosting ABI can do things like read and write arbitrary files on > the host system). However, it is sometimes useful to be able to run > trusted guest code which performs semihosting calls from guest > userspace, notably for test code. Add a command line suboption to > the existing semihosting-config option group so that you can > explicitly opt in to semihosting from guest userspace with > -semihosting-config userspace=on > > (There is no equivalent option for the user-mode emulator, because > there by definition all code runs in userspace and has access to > semihosting already.) > > This commit adds the infrastructure for the command line option and > adds a bool 'is_user' parameter to the function > semihosting_userspace_enabled() that target code can use to check > whether it should be permitting the semihosting call for userspace. > It mechanically makes all the callsites pass 'false', so they > continue checking "is semihosting enabled in general". Subsequent > commits will make each target that implements semihosting honour the > userspace=on option by passing the correct value and removing > whatever "don't do this for userspace" checking they were doing by > hand. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Acked-by: Alex Bennée <alex.bennee@linaro.org>
On Tue, Aug 16, 2022 at 5:03 AM Peter Maydell <peter.maydell@linaro.org> wrote: > > Currently our semihosting implementations generally prohibit use of > semihosting calls in system emulation from the guest userspace. This > is a very long standing behaviour justified originally "to provide > some semblance of security" (since code with access to the > semihosting ABI can do things like read and write arbitrary files on > the host system). However, it is sometimes useful to be able to run > trusted guest code which performs semihosting calls from guest > userspace, notably for test code. Add a command line suboption to > the existing semihosting-config option group so that you can > explicitly opt in to semihosting from guest userspace with > -semihosting-config userspace=on > > (There is no equivalent option for the user-mode emulator, because > there by definition all code runs in userspace and has access to > semihosting already.) > > This commit adds the infrastructure for the command line option and > adds a bool 'is_user' parameter to the function > semihosting_userspace_enabled() that target code can use to check > whether it should be permitting the semihosting call for userspace. > It mechanically makes all the callsites pass 'false', so they > continue checking "is semihosting enabled in general". Subsequent > commits will make each target that implements semihosting honour the > userspace=on option by passing the correct value and removing > whatever "don't do this for userspace" checking they were doing by > hand. > > Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alistair Francis <alistair.francis@wdc.com> Alistair > --- > include/semihosting/semihost.h | 10 ++++++++-- > semihosting/config.c | 10 ++++++++-- > softmmu/vl.c | 2 +- > stubs/semihost.c | 2 +- > target/arm/translate-a64.c | 2 +- > target/arm/translate.c | 6 +++--- > target/m68k/op_helper.c | 2 +- > target/nios2/translate.c | 2 +- > target/xtensa/translate.c | 6 +++--- > qemu-options.hx | 11 +++++++++-- > 10 files changed, 36 insertions(+), 17 deletions(-) > > diff --git a/include/semihosting/semihost.h b/include/semihosting/semihost.h > index 93a3c21b44d..efd2efa25ae 100644 > --- a/include/semihosting/semihost.h > +++ b/include/semihosting/semihost.h > @@ -27,7 +27,7 @@ typedef enum SemihostingTarget { > } SemihostingTarget; > > #ifdef CONFIG_USER_ONLY > -static inline bool semihosting_enabled(void) > +static inline bool semihosting_enabled(bool is_user) > { > return true; > } > @@ -52,7 +52,13 @@ static inline const char *semihosting_get_cmdline(void) > return NULL; > } > #else /* !CONFIG_USER_ONLY */ > -bool semihosting_enabled(void); > +/** > + * semihosting_enabled: > + * @is_user: true if guest code is in usermode (i.e. not privileged) > + * > + * Return true if guest code is allowed to make semihosting calls. > + */ > +bool semihosting_enabled(bool is_user); > SemihostingTarget semihosting_get_target(void); > const char *semihosting_get_arg(int i); > int semihosting_get_argc(void); > diff --git a/semihosting/config.c b/semihosting/config.c > index e171d4d6bc3..89a17596879 100644 > --- a/semihosting/config.c > +++ b/semihosting/config.c > @@ -34,6 +34,9 @@ QemuOptsList qemu_semihosting_config_opts = { > { > .name = "enable", > .type = QEMU_OPT_BOOL, > + }, { > + .name = "userspace", > + .type = QEMU_OPT_BOOL, > }, { > .name = "target", > .type = QEMU_OPT_STRING, > @@ -50,6 +53,7 @@ QemuOptsList qemu_semihosting_config_opts = { > > typedef struct SemihostingConfig { > bool enabled; > + bool userspace_enabled; > SemihostingTarget target; > char **argv; > int argc; > @@ -59,9 +63,9 @@ typedef struct SemihostingConfig { > static SemihostingConfig semihosting; > static const char *semihost_chardev; > > -bool semihosting_enabled(void) > +bool semihosting_enabled(bool is_user) > { > - return semihosting.enabled; > + return semihosting.enabled && (!is_user || semihosting.userspace_enabled); > } > > SemihostingTarget semihosting_get_target(void) > @@ -137,6 +141,8 @@ int qemu_semihosting_config_options(const char *optarg) > if (opts != NULL) { > semihosting.enabled = qemu_opt_get_bool(opts, "enable", > true); > + semihosting.userspace_enabled = qemu_opt_get_bool(opts, "userspace", > + false); > const char *target = qemu_opt_get(opts, "target"); > /* setup of chardev is deferred until they are initialised */ > semihost_chardev = qemu_opt_get(opts, "chardev"); > diff --git a/softmmu/vl.c b/softmmu/vl.c > index 706bd7cff79..3593f1d7821 100644 > --- a/softmmu/vl.c > +++ b/softmmu/vl.c > @@ -1822,7 +1822,7 @@ static void qemu_apply_machine_options(QDict *qdict) > { > object_set_properties_from_keyval(OBJECT(current_machine), qdict, false, &error_fatal); > > - if (semihosting_enabled() && !semihosting_get_argc()) { > + if (semihosting_enabled(false) && !semihosting_get_argc()) { > /* fall back to the -kernel/-append */ > semihosting_arg_fallback(current_machine->kernel_filename, current_machine->kernel_cmdline); > } > diff --git a/stubs/semihost.c b/stubs/semihost.c > index f486651afbb..d65c9fd5dcf 100644 > --- a/stubs/semihost.c > +++ b/stubs/semihost.c > @@ -23,7 +23,7 @@ QemuOptsList qemu_semihosting_config_opts = { > }; > > /* Queries to config status default to off */ > -bool semihosting_enabled(void) > +bool semihosting_enabled(bool is_user) > { > return false; > } > diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c > index 163df8c6157..3decc8da573 100644 > --- a/target/arm/translate-a64.c > +++ b/target/arm/translate-a64.c > @@ -2219,7 +2219,7 @@ static void disas_exc(DisasContext *s, uint32_t insn) > * it is required for halting debug disabled: it will UNDEF. > * Secondly, "HLT 0xf000" is the A64 semihosting syscall instruction. > */ > - if (semihosting_enabled() && imm16 == 0xf000) { > + if (semihosting_enabled(false) && imm16 == 0xf000) { > #ifndef CONFIG_USER_ONLY > /* In system mode, don't allow userspace access to semihosting, > * to provide some semblance of security (and for consistency > diff --git a/target/arm/translate.c b/target/arm/translate.c > index ad617b99481..b85be8a818d 100644 > --- a/target/arm/translate.c > +++ b/target/arm/translate.c > @@ -1169,7 +1169,7 @@ static inline void gen_hlt(DisasContext *s, int imm) > * semihosting, to provide some semblance of security > * (and for consistency with our 32-bit semihosting). > */ > - if (semihosting_enabled() && > + if (semihosting_enabled(false) && > #ifndef CONFIG_USER_ONLY > s->current_el != 0 && > #endif > @@ -6556,7 +6556,7 @@ static bool trans_BKPT(DisasContext *s, arg_BKPT *a) > /* BKPT is OK with ECI set and leaves it untouched */ > s->eci_handled = true; > if (arm_dc_feature(s, ARM_FEATURE_M) && > - semihosting_enabled() && > + semihosting_enabled(false) && > #ifndef CONFIG_USER_ONLY > !IS_USER(s) && > #endif > @@ -8764,7 +8764,7 @@ static bool trans_SVC(DisasContext *s, arg_SVC *a) > { > const uint32_t semihost_imm = s->thumb ? 0xab : 0x123456; > > - if (!arm_dc_feature(s, ARM_FEATURE_M) && semihosting_enabled() && > + if (!arm_dc_feature(s, ARM_FEATURE_M) && semihosting_enabled(false) && > #ifndef CONFIG_USER_ONLY > !IS_USER(s) && > #endif > diff --git a/target/m68k/op_helper.c b/target/m68k/op_helper.c > index d9937ca8dc5..4b3dfec1306 100644 > --- a/target/m68k/op_helper.c > +++ b/target/m68k/op_helper.c > @@ -203,7 +203,7 @@ static void cf_interrupt_all(CPUM68KState *env, int is_hw) > cf_rte(env); > return; > case EXCP_HALT_INSN: > - if (semihosting_enabled() > + if (semihosting_enabled(false) > && (env->sr & SR_S) != 0 > && (env->pc & 3) == 0 > && cpu_lduw_code(env, env->pc - 4) == 0x4e71 > diff --git a/target/nios2/translate.c b/target/nios2/translate.c > index 3a037a68cc4..2b556683422 100644 > --- a/target/nios2/translate.c > +++ b/target/nios2/translate.c > @@ -818,7 +818,7 @@ static void gen_break(DisasContext *dc, uint32_t code, uint32_t flags) > #ifndef CONFIG_USER_ONLY > /* The semihosting instruction is "break 1". */ > R_TYPE(instr, code); > - if (semihosting_enabled() && instr.imm5 == 1) { > + if (semihosting_enabled(false) && instr.imm5 == 1) { > t_gen_helper_raise_exception(dc, EXCP_SEMIHOST); > return; > } > diff --git a/target/xtensa/translate.c b/target/xtensa/translate.c > index 70e11eeb459..dc475a4274b 100644 > --- a/target/xtensa/translate.c > +++ b/target/xtensa/translate.c > @@ -2364,9 +2364,9 @@ static uint32_t test_exceptions_simcall(DisasContext *dc, > bool ill = true; > #else > /* Between RE.2 and RE.3 simcall opcode's become nop for the hardware. */ > - bool ill = dc->config->hw_version <= 250002 && !semihosting_enabled(); > + bool ill = dc->config->hw_version <= 250002 && !semihosting_enabled(false); > #endif > - if (ill || !semihosting_enabled()) { > + if (ill || !semihosting_enabled(false)) { > qemu_log_mask(LOG_GUEST_ERROR, "SIMCALL but semihosting is disabled\n"); > } > return ill ? XTENSA_OP_ILL : 0; > @@ -2376,7 +2376,7 @@ static void translate_simcall(DisasContext *dc, const OpcodeArg arg[], > const uint32_t par[]) > { > #ifndef CONFIG_USER_ONLY > - if (semihosting_enabled()) { > + if (semihosting_enabled(false)) { > gen_helper_simcall(cpu_env); > } > #endif > diff --git a/qemu-options.hx b/qemu-options.hx > index 3f23a42fa87..4e7111abe3d 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -4614,12 +4614,12 @@ SRST > information about the facilities this enables. > ERST > DEF("semihosting-config", HAS_ARG, QEMU_OPTION_semihosting_config, > - "-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,arg=str[,...]]\n" \ > + "-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]\n" \ > " semihosting configuration\n", > QEMU_ARCH_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | > QEMU_ARCH_MIPS | QEMU_ARCH_NIOS2 | QEMU_ARCH_RISCV) > SRST > -``-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,arg=str[,...]]`` > +``-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]`` > Enable and configure semihosting (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V > only). > > @@ -4646,6 +4646,13 @@ SRST > Send the output to a chardev backend output for native or auto > output when not in gdb > > + ``userspace=on|off`` > + Allows code running in guest userspace to access the semihosting > + interface. The default is that only privileged guest code can > + make semihosting calls. Note that setting ``userspace=on`` should > + only be used if all guest code is trusted (for example, in > + bare-metal test case code). > + > ``arg=str1,arg=str2,...`` > Allows the user to pass input arguments, and can be used > multiple times to build up a list. The old-style > -- > 2.25.1 > >
diff --git a/include/semihosting/semihost.h b/include/semihosting/semihost.h index 93a3c21b44d..efd2efa25ae 100644 --- a/include/semihosting/semihost.h +++ b/include/semihosting/semihost.h @@ -27,7 +27,7 @@ typedef enum SemihostingTarget { } SemihostingTarget; #ifdef CONFIG_USER_ONLY -static inline bool semihosting_enabled(void) +static inline bool semihosting_enabled(bool is_user) { return true; } @@ -52,7 +52,13 @@ static inline const char *semihosting_get_cmdline(void) return NULL; } #else /* !CONFIG_USER_ONLY */ -bool semihosting_enabled(void); +/** + * semihosting_enabled: + * @is_user: true if guest code is in usermode (i.e. not privileged) + * + * Return true if guest code is allowed to make semihosting calls. + */ +bool semihosting_enabled(bool is_user); SemihostingTarget semihosting_get_target(void); const char *semihosting_get_arg(int i); int semihosting_get_argc(void); diff --git a/semihosting/config.c b/semihosting/config.c index e171d4d6bc3..89a17596879 100644 --- a/semihosting/config.c +++ b/semihosting/config.c @@ -34,6 +34,9 @@ QemuOptsList qemu_semihosting_config_opts = { { .name = "enable", .type = QEMU_OPT_BOOL, + }, { + .name = "userspace", + .type = QEMU_OPT_BOOL, }, { .name = "target", .type = QEMU_OPT_STRING, @@ -50,6 +53,7 @@ QemuOptsList qemu_semihosting_config_opts = { typedef struct SemihostingConfig { bool enabled; + bool userspace_enabled; SemihostingTarget target; char **argv; int argc; @@ -59,9 +63,9 @@ typedef struct SemihostingConfig { static SemihostingConfig semihosting; static const char *semihost_chardev; -bool semihosting_enabled(void) +bool semihosting_enabled(bool is_user) { - return semihosting.enabled; + return semihosting.enabled && (!is_user || semihosting.userspace_enabled); } SemihostingTarget semihosting_get_target(void) @@ -137,6 +141,8 @@ int qemu_semihosting_config_options(const char *optarg) if (opts != NULL) { semihosting.enabled = qemu_opt_get_bool(opts, "enable", true); + semihosting.userspace_enabled = qemu_opt_get_bool(opts, "userspace", + false); const char *target = qemu_opt_get(opts, "target"); /* setup of chardev is deferred until they are initialised */ semihost_chardev = qemu_opt_get(opts, "chardev"); diff --git a/softmmu/vl.c b/softmmu/vl.c index 706bd7cff79..3593f1d7821 100644 --- a/softmmu/vl.c +++ b/softmmu/vl.c @@ -1822,7 +1822,7 @@ static void qemu_apply_machine_options(QDict *qdict) { object_set_properties_from_keyval(OBJECT(current_machine), qdict, false, &error_fatal); - if (semihosting_enabled() && !semihosting_get_argc()) { + if (semihosting_enabled(false) && !semihosting_get_argc()) { /* fall back to the -kernel/-append */ semihosting_arg_fallback(current_machine->kernel_filename, current_machine->kernel_cmdline); } diff --git a/stubs/semihost.c b/stubs/semihost.c index f486651afbb..d65c9fd5dcf 100644 --- a/stubs/semihost.c +++ b/stubs/semihost.c @@ -23,7 +23,7 @@ QemuOptsList qemu_semihosting_config_opts = { }; /* Queries to config status default to off */ -bool semihosting_enabled(void) +bool semihosting_enabled(bool is_user) { return false; } diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c index 163df8c6157..3decc8da573 100644 --- a/target/arm/translate-a64.c +++ b/target/arm/translate-a64.c @@ -2219,7 +2219,7 @@ static void disas_exc(DisasContext *s, uint32_t insn) * it is required for halting debug disabled: it will UNDEF. * Secondly, "HLT 0xf000" is the A64 semihosting syscall instruction. */ - if (semihosting_enabled() && imm16 == 0xf000) { + if (semihosting_enabled(false) && imm16 == 0xf000) { #ifndef CONFIG_USER_ONLY /* In system mode, don't allow userspace access to semihosting, * to provide some semblance of security (and for consistency diff --git a/target/arm/translate.c b/target/arm/translate.c index ad617b99481..b85be8a818d 100644 --- a/target/arm/translate.c +++ b/target/arm/translate.c @@ -1169,7 +1169,7 @@ static inline void gen_hlt(DisasContext *s, int imm) * semihosting, to provide some semblance of security * (and for consistency with our 32-bit semihosting). */ - if (semihosting_enabled() && + if (semihosting_enabled(false) && #ifndef CONFIG_USER_ONLY s->current_el != 0 && #endif @@ -6556,7 +6556,7 @@ static bool trans_BKPT(DisasContext *s, arg_BKPT *a) /* BKPT is OK with ECI set and leaves it untouched */ s->eci_handled = true; if (arm_dc_feature(s, ARM_FEATURE_M) && - semihosting_enabled() && + semihosting_enabled(false) && #ifndef CONFIG_USER_ONLY !IS_USER(s) && #endif @@ -8764,7 +8764,7 @@ static bool trans_SVC(DisasContext *s, arg_SVC *a) { const uint32_t semihost_imm = s->thumb ? 0xab : 0x123456; - if (!arm_dc_feature(s, ARM_FEATURE_M) && semihosting_enabled() && + if (!arm_dc_feature(s, ARM_FEATURE_M) && semihosting_enabled(false) && #ifndef CONFIG_USER_ONLY !IS_USER(s) && #endif diff --git a/target/m68k/op_helper.c b/target/m68k/op_helper.c index d9937ca8dc5..4b3dfec1306 100644 --- a/target/m68k/op_helper.c +++ b/target/m68k/op_helper.c @@ -203,7 +203,7 @@ static void cf_interrupt_all(CPUM68KState *env, int is_hw) cf_rte(env); return; case EXCP_HALT_INSN: - if (semihosting_enabled() + if (semihosting_enabled(false) && (env->sr & SR_S) != 0 && (env->pc & 3) == 0 && cpu_lduw_code(env, env->pc - 4) == 0x4e71 diff --git a/target/nios2/translate.c b/target/nios2/translate.c index 3a037a68cc4..2b556683422 100644 --- a/target/nios2/translate.c +++ b/target/nios2/translate.c @@ -818,7 +818,7 @@ static void gen_break(DisasContext *dc, uint32_t code, uint32_t flags) #ifndef CONFIG_USER_ONLY /* The semihosting instruction is "break 1". */ R_TYPE(instr, code); - if (semihosting_enabled() && instr.imm5 == 1) { + if (semihosting_enabled(false) && instr.imm5 == 1) { t_gen_helper_raise_exception(dc, EXCP_SEMIHOST); return; } diff --git a/target/xtensa/translate.c b/target/xtensa/translate.c index 70e11eeb459..dc475a4274b 100644 --- a/target/xtensa/translate.c +++ b/target/xtensa/translate.c @@ -2364,9 +2364,9 @@ static uint32_t test_exceptions_simcall(DisasContext *dc, bool ill = true; #else /* Between RE.2 and RE.3 simcall opcode's become nop for the hardware. */ - bool ill = dc->config->hw_version <= 250002 && !semihosting_enabled(); + bool ill = dc->config->hw_version <= 250002 && !semihosting_enabled(false); #endif - if (ill || !semihosting_enabled()) { + if (ill || !semihosting_enabled(false)) { qemu_log_mask(LOG_GUEST_ERROR, "SIMCALL but semihosting is disabled\n"); } return ill ? XTENSA_OP_ILL : 0; @@ -2376,7 +2376,7 @@ static void translate_simcall(DisasContext *dc, const OpcodeArg arg[], const uint32_t par[]) { #ifndef CONFIG_USER_ONLY - if (semihosting_enabled()) { + if (semihosting_enabled(false)) { gen_helper_simcall(cpu_env); } #endif diff --git a/qemu-options.hx b/qemu-options.hx index 3f23a42fa87..4e7111abe3d 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4614,12 +4614,12 @@ SRST information about the facilities this enables. ERST DEF("semihosting-config", HAS_ARG, QEMU_OPTION_semihosting_config, - "-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,arg=str[,...]]\n" \ + "-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]\n" \ " semihosting configuration\n", QEMU_ARCH_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | QEMU_ARCH_MIPS | QEMU_ARCH_NIOS2 | QEMU_ARCH_RISCV) SRST -``-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,arg=str[,...]]`` +``-semihosting-config [enable=on|off][,target=native|gdb|auto][,chardev=id][,userspace=on|off][,arg=str[,...]]`` Enable and configure semihosting (ARM, M68K, Xtensa, MIPS, Nios II, RISC-V only). @@ -4646,6 +4646,13 @@ SRST Send the output to a chardev backend output for native or auto output when not in gdb + ``userspace=on|off`` + Allows code running in guest userspace to access the semihosting + interface. The default is that only privileged guest code can + make semihosting calls. Note that setting ``userspace=on`` should + only be used if all guest code is trusted (for example, in + bare-metal test case code). + ``arg=str1,arg=str2,...`` Allows the user to pass input arguments, and can be used multiple times to build up a list. The old-style
Currently our semihosting implementations generally prohibit use of semihosting calls in system emulation from the guest userspace. This is a very long standing behaviour justified originally "to provide some semblance of security" (since code with access to the semihosting ABI can do things like read and write arbitrary files on the host system). However, it is sometimes useful to be able to run trusted guest code which performs semihosting calls from guest userspace, notably for test code. Add a command line suboption to the existing semihosting-config option group so that you can explicitly opt in to semihosting from guest userspace with -semihosting-config userspace=on (There is no equivalent option for the user-mode emulator, because there by definition all code runs in userspace and has access to semihosting already.) This commit adds the infrastructure for the command line option and adds a bool 'is_user' parameter to the function semihosting_userspace_enabled() that target code can use to check whether it should be permitting the semihosting call for userspace. It mechanically makes all the callsites pass 'false', so they continue checking "is semihosting enabled in general". Subsequent commits will make each target that implements semihosting honour the userspace=on option by passing the correct value and removing whatever "don't do this for userspace" checking they were doing by hand. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- include/semihosting/semihost.h | 10 ++++++++-- semihosting/config.c | 10 ++++++++-- softmmu/vl.c | 2 +- stubs/semihost.c | 2 +- target/arm/translate-a64.c | 2 +- target/arm/translate.c | 6 +++--- target/m68k/op_helper.c | 2 +- target/nios2/translate.c | 2 +- target/xtensa/translate.c | 6 +++--- qemu-options.hx | 11 +++++++++-- 10 files changed, 36 insertions(+), 17 deletions(-)