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

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>
This commit is contained in:
Kees Cook 2018-05-03 14:56:12 -07:00 committed by Thomas Gleixner
parent b849a812f7
commit 00a02d0c50
4 changed files with 36 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/seccomp.h
View File

@ -4,8 +4,9 @@
#include <uapi/linux/seccomp.h>
#define SECCOMP_FILTER_FLAG_MASK (SECCOMP_FILTER_FLAG_TSYNC | \
SECCOMP_FILTER_FLAG_LOG)
#define SECCOMP_FILTER_FLAG_MASK (SECCOMP_FILTER_FLAG_TSYNC | \
SECCOMP_FILTER_FLAG_LOG | \
SECCOMP_FILTER_FLAG_SPEC_ALLOW)
#ifdef CONFIG_SECCOMP

5
include/uapi/linux/seccomp.h
View File

@ -17,8 +17,9 @@
#define SECCOMP_GET_ACTION_AVAIL 2
/* Valid flags for SECCOMP_SET_MODE_FILTER */
#define SECCOMP_FILTER_FLAG_TSYNC 1
#define SECCOMP_FILTER_FLAG_LOG 2
#define SECCOMP_FILTER_FLAG_TSYNC (1UL << 0)
#define SECCOMP_FILTER_FLAG_LOG (1UL << 1)
#define SECCOMP_FILTER_FLAG_SPEC_ALLOW (1UL << 2)
/*
* All BPF programs must return a 32-bit value.

19
kernel/seccomp.c
View File

@ -243,7 +243,8 @@ 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);
@ -253,8 +254,9 @@ 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);
}
@ -322,7 +324,7 @@ 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;
@ -363,7 +365,8 @@ 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);
}
}
@ -486,7 +489,7 @@ 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;
}
@ -835,7 +838,7 @@ 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:
@ -893,7 +896,7 @@ 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)

22
tools/testing/selftests/seccomp/seccomp_bpf.c
View File

@ -134,11 +134,15 @@ struct seccomp_data {
#endif
#ifndef SECCOMP_FILTER_FLAG_TSYNC
#define SECCOMP_FILTER_FLAG_TSYNC 1
#define SECCOMP_FILTER_FLAG_TSYNC (1UL << 0)
#endif
#ifndef SECCOMP_FILTER_FLAG_LOG
#define SECCOMP_FILTER_FLAG_LOG 2
#define SECCOMP_FILTER_FLAG_LOG (1UL << 1)
#endif
#ifndef SECCOMP_FILTER_FLAG_SPEC_ALLOW
#define SECCOMP_FILTER_FLAG_SPEC_ALLOW (1UL << 2)
#endif
#ifndef PTRACE_SECCOMP_GET_METADATA
@ -2072,14 +2076,26 @@ TEST(seccomp_syscall_mode_lock)
TEST(detect_seccomp_filter_flags)
{
unsigned int flags[] = { SECCOMP_FILTER_FLAG_TSYNC,
SECCOMP_FILTER_FLAG_LOG };
SECCOMP_FILTER_FLAG_LOG,
SECCOMP_FILTER_FLAG_SPEC_ALLOW };
unsigned int flag, all_flags;
int i;
long ret;
/* Test detection of known-good filter flags */
for (i = 0, all_flags = 0; i < ARRAY_SIZE(flags); i++) {
int bits = 0;
flag = flags[i];
/* Make sure the flag is a single bit! */
while (flag) {
if (flag & 0x1)
bits ++;
flag >>= 1;
}
ASSERT_EQ(1, bits);
flag = flags[i];
ret = seccomp(SECCOMP_SET_MODE_FILTER, flag, NULL);
ASSERT_NE(ENOSYS, errno) {
TH_LOG("Kernel does not support seccomp syscall!");