diff options
Diffstat (limited to 'arch/x86/mm/tlb.c')
| -rw-r--r-- | arch/x86/mm/tlb.c | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 7d68489cfdb1..bddd6b3cee1d 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) { @@ -286,18 +300,13 @@ 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)) { |