[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAG48ez23G+wcnkCMNZV_mxYMS=h+pZkpx1451Wz5GB9_tcDv3Q@mail.gmail.com>
Date: Sat, 18 Aug 2018 01:55:02 +0200
From: Jann Horn <jannh@...gle.com>
To: Casey Schaufler <casey.schaufler@...el.com>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
kernel list <linux-kernel@...r.kernel.org>,
linux-security-module <linux-security-module@...r.kernel.org>, selinux@...ho.nsa.gov,
Dave Hansen <dave.hansen@...el.com>, deneen.t.dock@...el.com, kristen@...ux.intel.com,
Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH RFC v2 2/5] X86: Support LSM determination of side-channel vulnerability
On Sat, Aug 18, 2018 at 12:17 AM Casey Schaufler
<casey.schaufler@...el.com> wrote:
>
> From: Casey Schaufler <cschaufler@...alhost.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@...el.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();
> + }
When you posted v1 of this series, I asked:
| 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?
Have you addressed that? I don't see it...
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
