| Message ID | 20180815235355.14908-3-casey.schaufler@intel.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | LSM: Add and use a hook for side-channel safety checks | expand |
On Thu, Aug 16, 2018 at 11:51 AM Casey Schaufler <casey.schaufler@intel.com> wrote: > > From: Casey Schaufler <cschaufler@localhost.localdomain> > > When switching between tasks it may be necessary > to set an indirect branch prediction barrier if the > tasks are potentially vulnerable to side-channel > attacks. This adds a call to security_task_safe_sidechannel > so that security modules can weigh in on the decision. > > Signed-off-by: Casey Schaufler <casey.schaufler@intel.com> > --- > arch/x86/mm/tlb.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index 6eb1f34c3c85..8714d4af06aa 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/security.h> > > #include <asm/tlbflush.h> > #include <asm/mmu_context.h> > @@ -270,11 +271,14 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, > * 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. > + * If a security module thinks that the transition > + * is unsafe do the flush. > */ > - if (tsk && tsk->mm && > - tsk->mm->context.ctx_id != last_ctx_id && > - get_dumpable(tsk->mm) != SUID_DUMP_USER) > - indirect_branch_prediction_barrier(); > + if (tsk && tsk->mm && tsk->mm->context.ctx_id != last_ctx_id) { > + if (get_dumpable(tsk->mm) != SUID_DUMP_USER || > + security_task_safe_sidechannel(tsk) != 0) > + indirect_branch_prediction_barrier(); > + } Does this enforce transitivity? What happens if we first switch from an attacker task to a task without ->mm, and immediately afterwards from the task without ->mm to a victim task? In that case, whether a flush happens between the attacker task and the victim task depends on whether the LSM thinks that the mm-less task should have access to the victim task, right?
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 6eb1f34c3c85..8714d4af06aa 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/security.h> #include <asm/tlbflush.h> #include <asm/mmu_context.h> @@ -270,11 +271,14 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * 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. + * If a security module thinks that the transition + * is unsafe do the flush. */ - if (tsk && tsk->mm && - tsk->mm->context.ctx_id != last_ctx_id && - get_dumpable(tsk->mm) != SUID_DUMP_USER) - indirect_branch_prediction_barrier(); + if (tsk && tsk->mm && tsk->mm->context.ctx_id != last_ctx_id) { + if (get_dumpable(tsk->mm) != SUID_DUMP_USER || + security_task_safe_sidechannel(tsk) != 0) + indirect_branch_prediction_barrier(); + } if (IS_ENABLED(CONFIG_VMAP_STACK)) { /*