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seccomp: Add filter flag to opt-out of SSB mitigation

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commit 00a02d0c502a06d15e07b857f8ff921e3e402675 upstream

If a seccomp user is not interested in Speculative Store Bypass mitigation
by default, it can set the new SECCOMP_FILTER_FLAG_SPEC_ALLOW flag when
adding filters.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook 2018-05-03 14:56:12 -07:00 • committed by Greg Kroah-Hartman
parent c71def81cd
commit ab677c2add
4 changed files with 93 additions and 11 deletions
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19
kernel/seccomp.c
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@ -230,7 +230,8 @@ static inline void spec_mitigate(struct task_struct *task,
}
static inline void seccomp_assign_mode(struct task_struct *task,
unsigned long seccomp_mode)
unsigned long seccomp_mode,
unsigned long flags)
{
assert_spin_locked(&task->sighand->siglock);
@ -240,8 +241,9 @@ static inline void seccomp_assign_mode(struct task_struct *task,
* filter) is set.
*/
smp_mb__before_atomic();
/* Assume seccomp processes want speculation flaw mitigation. */
spec_mitigate(task, PR_SPEC_STORE_BYPASS);
/* Assume default seccomp processes want spec flaw mitigation. */
if ((flags & SECCOMP_FILTER_FLAG_SPEC_ALLOW) == 0)
spec_mitigate(task, PR_SPEC_STORE_BYPASS);
set_tsk_thread_flag(task, TIF_SECCOMP);
}
@ -309,7 +311,7 @@ static inline pid_t seccomp_can_sync_threads(void)
* without dropping the locks.
*
*/
static inline void seccomp_sync_threads(void)
static inline void seccomp_sync_threads(unsigned long flags)
{
struct task_struct *thread, *caller;
@ -350,7 +352,8 @@ static inline void seccomp_sync_threads(void)
* allow one thread to transition the other.
*/
if (thread->seccomp.mode == SECCOMP_MODE_DISABLED)
seccomp_assign_mode(thread, SECCOMP_MODE_FILTER);
seccomp_assign_mode(thread, SECCOMP_MODE_FILTER,
flags);
}
}
@ -469,7 +472,7 @@ static long seccomp_attach_filter(unsigned int flags,
/* Now that the new filter is in place, synchronize to all threads. */
if (flags & SECCOMP_FILTER_FLAG_TSYNC)
seccomp_sync_threads();
seccomp_sync_threads(flags);
return 0;
}
@ -729,7 +732,7 @@ static long seccomp_set_mode_strict(void)
#ifdef TIF_NOTSC
disable_TSC();
#endif
seccomp_assign_mode(current, seccomp_mode);
seccomp_assign_mode(current, seccomp_mode, 0);
ret = 0;
out:
@ -787,7 +790,7 @@ static long seccomp_set_mode_filter(unsigned int flags,
/* Do not free the successfully attached filter. */
prepared = NULL;
seccomp_assign_mode(current, seccomp_mode);
seccomp_assign_mode(current, seccomp_mode, flags);
out:
spin_unlock_irq(&current->sighand->siglock);
if (flags & SECCOMP_FILTER_FLAG_TSYNC)