Create PRCTL interface to restrict an application's indirect branch speculation. This will protect the application against spectre v2 attack from another application.
Invocations: Check indirect branch speculation status with - prctl(PR_GET_SPECULATION_CTRL, PR_INDIR_BRANCH, 0, 0, 0); Enable indirect branch speculation with - prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0); Disable indirect branch speculation with - prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0); Force disable indirect branch speculation with - prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0); See Documentation/userspace-api/spec_ctrl.rst. Signed-off-by: Tim Chen <[email protected]> --- Documentation/admin-guide/kernel-parameters.txt | 5 +- Documentation/userspace-api/spec_ctrl.rst | 10 +++ arch/x86/kernel/cpu/bugs.c | 85 ++++++++++++++++++++++++- include/linux/sched.h | 11 ++++ include/uapi/linux/prctl.h | 1 + tools/include/uapi/linux/prctl.h | 1 + 6 files changed, 111 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2feb6b2..9af11be 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4196,7 +4196,10 @@ lite - turn on mitigation for non-dumpable processes (i.e. protect daemons and other privileged processes that tend to be - non-dumpable). + non-dumpable), and processes that has indirect + branch speculation restricted via prctl's + PR_SET_SPECULATION_CTRL option + strict - protect against attacks for all user processes auto - let kernel decide lite or strict mode diff --git a/Documentation/userspace-api/spec_ctrl.rst b/Documentation/userspace-api/spec_ctrl.rst index 32f3d55..1acf198 100644 --- a/Documentation/userspace-api/spec_ctrl.rst +++ b/Documentation/userspace-api/spec_ctrl.rst @@ -92,3 +92,13 @@ Speculation misfeature controls * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0); * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0); * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0); + +- PR_INDIR_BRANCH: Indirect Branch Speculation in Applications + (Mitigate Spectre V2 style user space application + to application attack) + + Invocations: + * prctl(PR_GET_SPECULATION_CTRL, PR_INDIR_BRANCH, 0, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0); diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index cc77b9e..d5c5faf 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -763,12 +763,70 @@ static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl) return 0; } +static int indir_branch_prctl_set(struct task_struct *task, unsigned long ctrl) +{ + bool update; + + switch (ctrl) { + case PR_SPEC_ENABLE: + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE) + return 0; + /* + * Indirect branch speculation is always disabled in + * strict mode or if the application is non dumpable + * in lite mode. + */ + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_STRICT) + return -ENXIO; + if (task->mm && get_dumpable(task->mm) != SUID_DUMP_USER) + return -ENXIO; + task_clear_spec_indir_branch_disable(task); + update = test_and_clear_tsk_thread_flag(task, TIF_STIBP); + break; + case PR_SPEC_DISABLE: + /* + * Indirect branch speculation is always enabled when + * app to app mitigation is off. + */ + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE) + return -ENXIO; + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_STRICT) + return 0; + task_set_spec_indir_branch_disable(task); + update = !test_and_set_tsk_thread_flag(task, TIF_STIBP); + break; + case PR_SPEC_FORCE_DISABLE: + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE) + return -ENXIO; + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_STRICT) + return 0; + task_set_spec_indir_branch_disable(task); + task_set_spec_indir_branch_force_disable(task); + update = !test_and_set_tsk_thread_flag(task, TIF_STIBP); + break; + default: + return -ERANGE; + } + + /* + * If being set on non-current task, delay setting the CPU + * mitigation until it is next scheduled. + * Use speculative_store_bypass_update will update SPEC_CTRL MSR + */ + if (task == current && update) + speculation_ctrl_update_current(); + + return 0; +} + int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which, unsigned long ctrl) { switch (which) { case PR_SPEC_STORE_BYPASS: return ssb_prctl_set(task, ctrl); + case PR_INDIR_BRANCH: + return indir_branch_prctl_set(task, ctrl); default: return -ENODEV; } @@ -787,7 +845,7 @@ void arch_set_dumpable(struct task_struct *tsk, unsigned int value) if (tsk->mm && value != SUID_DUMP_USER) update = !test_and_set_tsk_thread_flag(tsk, TIF_STIBP); - else + else if (!task_spec_indir_branch_disable(tsk)) update = test_and_clear_tsk_thread_flag(tsk, TIF_STIBP); if (tsk == current && update) @@ -821,11 +879,36 @@ static int ssb_prctl_get(struct task_struct *task) } } +static int indir_branch_prctl_get(struct task_struct *task) +{ + if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) + return PR_SPEC_NOT_AFFECTED; + + switch (spectre_v2_app2app_enabled) { + case SPECTRE_V2_APP2APP_NONE: + return PR_SPEC_ENABLE; + case SPECTRE_V2_APP2APP_LITE: + if (task_spec_indir_branch_force_disable(task)) + return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE; + if (task->mm && get_dumpable(task->mm) != SUID_DUMP_USER) + return PR_SPEC_DISABLE; + if (task_spec_indir_branch_disable(task)) + return PR_SPEC_PRCTL | PR_SPEC_DISABLE; + return PR_SPEC_PRCTL | PR_SPEC_ENABLE; + case SPECTRE_V2_APP2APP_STRICT: + return PR_SPEC_DISABLE; + default: + return PR_SPEC_NOT_AFFECTED; + } +} + int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which) { switch (which) { case PR_SPEC_STORE_BYPASS: return ssb_prctl_get(task); + case PR_INDIR_BRANCH: + return indir_branch_prctl_get(task); default: return -ENODEV; } diff --git a/include/linux/sched.h b/include/linux/sched.h index 977cb57..8e44de6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1439,6 +1439,10 @@ static inline bool is_percpu_thread(void) #define PFA_SPREAD_SLAB 2 /* Spread some slab caches over cpuset */ #define PFA_SPEC_SSB_DISABLE 3 /* Speculative Store Bypass disabled */ #define PFA_SPEC_SSB_FORCE_DISABLE 4 /* Speculative Store Bypass force disabled*/ +#define PFA_SPEC_INDIR_BRANCH_DISABLE 5 /* Indirect branch speculation */ + /* restricted in apps */ +#define PFA_SPEC_INDIR_BRANCH_FORCE_DISABLE 6 /* Indirect branch speculation */ + /* restricted in apps force disabled */ #define TASK_PFA_TEST(name, func) \ static inline bool task_##func(struct task_struct *p) \ @@ -1470,6 +1474,13 @@ TASK_PFA_CLEAR(SPEC_SSB_DISABLE, spec_ssb_disable) TASK_PFA_TEST(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable) TASK_PFA_SET(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable) +TASK_PFA_TEST(SPEC_INDIR_BRANCH_DISABLE, spec_indir_branch_disable) +TASK_PFA_SET(SPEC_INDIR_BRANCH_DISABLE, spec_indir_branch_disable) +TASK_PFA_CLEAR(SPEC_INDIR_BRANCH_DISABLE, spec_indir_branch_disable) + +TASK_PFA_TEST(SPEC_INDIR_BRANCH_FORCE_DISABLE, spec_indir_branch_force_disable) +TASK_PFA_SET(SPEC_INDIR_BRANCH_FORCE_DISABLE, spec_indir_branch_force_disable) + static inline void current_restore_flags(unsigned long orig_flags, unsigned long flags) { diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index c0d7ea0..06f71f6 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -212,6 +212,7 @@ struct prctl_mm_map { #define PR_SET_SPECULATION_CTRL 53 /* Speculation control variants */ # define PR_SPEC_STORE_BYPASS 0 +# define PR_INDIR_BRANCH 1 /* Return and control values for PR_SET/GET_SPECULATION_CTRL */ # define PR_SPEC_NOT_AFFECTED 0 # define PR_SPEC_PRCTL (1UL << 0) diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h index c0d7ea0..06f71f6 100644 --- a/tools/include/uapi/linux/prctl.h +++ b/tools/include/uapi/linux/prctl.h @@ -212,6 +212,7 @@ struct prctl_mm_map { #define PR_SET_SPECULATION_CTRL 53 /* Speculation control variants */ # define PR_SPEC_STORE_BYPASS 0 +# define PR_INDIR_BRANCH 1 /* Return and control values for PR_SET/GET_SPECULATION_CTRL */ # define PR_SPEC_NOT_AFFECTED 0 # define PR_SPEC_PRCTL (1UL << 0) -- 2.9.4
