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-rw-r--r--arch/x86/mm/tlb.c31
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)) {