diff options
| -rw-r--r-- | arch/x86/mm/tlb.c | 31 | ||||
| -rw-r--r-- | include/linux/ptrace.h | 21 | ||||
| -rw-r--r-- | kernel/ptrace.c | 10 |
3 files changed, 49 insertions, 13 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index e96b99eb800c..073b8df349a0 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -7,6 +7,7 @@ #include <linux/export.h> #include <linux/cpu.h> #include <linux/debugfs.h> +#include <linux/ptrace.h> #include <asm/tlbflush.h> #include <asm/mmu_context.h> @@ -180,6 +181,19 @@ static void sync_current_stack_to_mm(struct mm_struct *mm) } } +static bool ibpb_needed(struct task_struct *tsk, u64 last_ctx_id) +{ + /* + * Check if the current (previous) task has access to the memory + * of the @tsk (next) task. If access is denied, make sure to + * issue a IBPB to stop user->user Spectre-v2 attacks. + * + * Note: __ptrace_may_access() returns 0 or -ERRNO. + */ + return (tsk && tsk->mm && tsk->mm->context.ctx_id != last_ctx_id && + ptrace_may_access_sched(tsk, PTRACE_MODE_SPEC_IBPB)); +} + void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk) { @@ -262,18 +276,13 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * one process from doing Spectre-v2 attacks on another. * * As an optimization, flush indirect branches only when - * switching into processes that disable dumping. This - * protects high value processes like gpg, without having - * too high performance overhead. IBPB is *expensive*! - * - * This will not flush branches when switching into kernel - * threads. It will also not flush if we switch to idle - * thread and back to the same process. It will flush if we - * switch to a different non-dumpable process. + * switching into a processes that can't be ptrace by the + * current one (as in such case, attacker has much more + * convenient way how to tamper with the next process than + * branch buffer poisoning). */ - if (tsk && tsk->mm && - tsk->mm->context.ctx_id != last_ctx_id && - get_dumpable(tsk->mm) != SUID_DUMP_USER) + if (static_cpu_has(X86_FEATURE_USE_IBPB) && + ibpb_needed(tsk, last_ctx_id)) indirect_branch_prediction_barrier(); if (IS_ENABLED(CONFIG_VMAP_STACK)) { diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index 4f36431c380b..e5e5ef513df3 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -62,14 +62,17 @@ extern void exit_ptrace(struct task_struct *tracer, struct list_head *dead); #define PTRACE_MODE_READ 0x01 #define PTRACE_MODE_ATTACH 0x02 #define PTRACE_MODE_NOAUDIT 0x04 -#define PTRACE_MODE_FSCREDS 0x08 -#define PTRACE_MODE_REALCREDS 0x10 +#define PTRACE_MODE_FSCREDS 0x08 +#define PTRACE_MODE_REALCREDS 0x10 +#define PTRACE_MODE_SCHED 0x20 +#define PTRACE_MODE_IBPB 0x40 /* shorthands for READ/ATTACH and FSCREDS/REALCREDS combinations */ #define PTRACE_MODE_READ_FSCREDS (PTRACE_MODE_READ | PTRACE_MODE_FSCREDS) #define PTRACE_MODE_READ_REALCREDS (PTRACE_MODE_READ | PTRACE_MODE_REALCREDS) #define PTRACE_MODE_ATTACH_FSCREDS (PTRACE_MODE_ATTACH | PTRACE_MODE_FSCREDS) #define PTRACE_MODE_ATTACH_REALCREDS (PTRACE_MODE_ATTACH | PTRACE_MODE_REALCREDS) +#define PTRACE_MODE_SPEC_IBPB (PTRACE_MODE_ATTACH_REALCREDS | PTRACE_MODE_IBPB) /** * ptrace_may_access - check whether the caller is permitted to access @@ -87,6 +90,20 @@ extern void exit_ptrace(struct task_struct *tracer, struct list_head *dead); */ extern bool ptrace_may_access(struct task_struct *task, unsigned int mode); +/** + * ptrace_may_access - check whether the caller is permitted to access + * a target task. + * @task: target task + * @mode: selects type of access and caller credentials + * + * Returns true on success, false on denial. + * + * Similar to ptrace_may_access(). Only to be called from context switch + * code. Does not call into audit and the regular LSM hooks due to locking + * constraints. + */ +extern bool ptrace_may_access_sched(struct task_struct *task, unsigned int mode); + static inline int ptrace_reparented(struct task_struct *child) { return !same_thread_group(child->real_parent, child->parent); diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 21fec73d45d4..99cfddde6a55 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -261,6 +261,9 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state) static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode) { + if (mode & PTRACE_MODE_SCHED) + return false; + if (mode & PTRACE_MODE_NOAUDIT) return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE); else @@ -328,9 +331,16 @@ ok: !ptrace_has_cap(mm->user_ns, mode))) return -EPERM; + if (mode & PTRACE_MODE_SCHED) + return 0; return security_ptrace_access_check(task, mode); } +bool ptrace_may_access_sched(struct task_struct *task, unsigned int mode) +{ + return __ptrace_may_access(task, mode | PTRACE_MODE_SCHED); +} + bool ptrace_may_access(struct task_struct *task, unsigned int mode) { int err; |