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x86/speculation: Add prctl() control for indirect branch speculation 

Add the PR_SPEC_INDIRECT_BRANCH option for the PR_GET_SPECULATION_CTRL and
PR_SET_SPECULATION_CTRL prctls to allow fine grained per task control of
indirect branch speculation via STIBP and IBPB.

Invocations:
 Check indirect branch speculation status with
 - prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, 0, 0, 0);

 Enable indirect branch speculation with
 - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_ENABLE, 0, 0);

 Disable indirect branch speculation with
 - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE, 0, 0);

 Force disable indirect branch speculation with
 - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);

See Documentation/userspace-api/spec_ctrl.rst.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Casey Schaufler <casey.schaufler@intel.com>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Waiman Long <longman9394@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Dave Stewart <david.c.stewart@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185005.866780996@linutronix.de
hifive-unleashed-5.1
Thomas Gleixner 2018-11-25 19:33:53 +01:00
parent 6893a959d7
commit 9137bb27e6
7 changed files with 93 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
Documentation/userspace-api/spec_ctrl.rst
View File

@ -92,3 +92,12 @@ Speculation misfeature controls
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);
- PR_SPEC_INDIR_BRANCH: Indirect Branch Speculation in User Processes
(Mitigate Spectre V2 style attacks against user processes)
Invocations:
* prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, 0, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_ENABLE, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);

1
arch/x86/include/asm/nospec-branch.h
View File

@ -232,6 +232,7 @@ enum spectre_v2_mitigation {
enum spectre_v2_user_mitigation {
SPECTRE_V2_USER_NONE,
SPECTRE_V2_USER_STRICT,
SPECTRE_V2_USER_PRCTL,
};
/* The Speculative Store Bypass disable variants */

67
arch/x86/kernel/cpu/bugs.c
View File

@ -566,6 +566,8 @@ void arch_smt_update(void)
case SPECTRE_V2_USER_STRICT:
update_stibp_strict();
break;
case SPECTRE_V2_USER_PRCTL:
break;
}
mutex_unlock(&spec_ctrl_mutex);
@ -752,12 +754,50 @@ static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
return 0;
}
static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
{
switch (ctrl) {
case PR_SPEC_ENABLE:
if (spectre_v2_user == SPECTRE_V2_USER_NONE)
return 0;
/*
* Indirect branch speculation is always disabled in strict
* mode.
*/
if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
return -EPERM;
task_clear_spec_ib_disable(task);
task_update_spec_tif(task);
break;
case PR_SPEC_DISABLE:
case PR_SPEC_FORCE_DISABLE:
/*
* Indirect branch speculation is always allowed when
* mitigation is force disabled.
*/
if (spectre_v2_user == SPECTRE_V2_USER_NONE)
return -EPERM;
if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
return 0;
task_set_spec_ib_disable(task);
if (ctrl == PR_SPEC_FORCE_DISABLE)
task_set_spec_ib_force_disable(task);
task_update_spec_tif(task);
break;
default:
return -ERANGE;
}
return 0;
}
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
unsigned long ctrl)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_set(task, ctrl);
case PR_SPEC_INDIRECT_BRANCH:
return ib_prctl_set(task, ctrl);
default:
return -ENODEV;
}
@ -790,11 +830,34 @@ static int ssb_prctl_get(struct task_struct *task)
}
}
static int ib_prctl_get(struct task_struct *task)
{
if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
return PR_SPEC_NOT_AFFECTED;
switch (spectre_v2_user) {
case SPECTRE_V2_USER_NONE:
return PR_SPEC_ENABLE;
case SPECTRE_V2_USER_PRCTL:
if (task_spec_ib_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
if (task_spec_ib_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
case SPECTRE_V2_USER_STRICT:
return PR_SPEC_DISABLE;
default:
return PR_SPEC_NOT_AFFECTED;
}
}
int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssb_prctl_get(task);
case PR_SPEC_INDIRECT_BRANCH:
return ib_prctl_get(task);
default:
return -ENODEV;
}
@ -974,6 +1037,8 @@ static char *stibp_state(void)
return ", STIBP: disabled";
case SPECTRE_V2_USER_STRICT:
return ", STIBP: forced";
case SPECTRE_V2_USER_PRCTL:
return "";
}
return "";
}
@ -986,6 +1051,8 @@ static char *ibpb_state(void)
return ", IBPB: disabled";
case SPECTRE_V2_USER_STRICT:
return ", IBPB: always-on";
case SPECTRE_V2_USER_PRCTL:
return "";
}
}
return "";

5
arch/x86/kernel/process.c
View File

@ -450,6 +450,11 @@ static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
set_tsk_thread_flag(tsk, TIF_SSBD);
else
clear_tsk_thread_flag(tsk, TIF_SSBD);
if (task_spec_ib_disable(tsk))
set_tsk_thread_flag(tsk, TIF_SPEC_IB);
else
clear_tsk_thread_flag(tsk, TIF_SPEC_IB);
}
/* Return the updated threadinfo flags*/
return task_thread_info(tsk)->flags;

9
include/linux/sched.h
View File

@ -1453,6 +1453,8 @@ static inline bool is_percpu_thread(void)
#define PFA_SPREAD_SLAB 2 /* Spread some slab caches over cpuset */
#define PFA_SPEC_SSB_DISABLE 3 /* Speculative Store Bypass disabled */
#define PFA_SPEC_SSB_FORCE_DISABLE 4 /* Speculative Store Bypass force disabled*/
#define PFA_SPEC_IB_DISABLE 5 /* Indirect branch speculation restricted */
#define PFA_SPEC_IB_FORCE_DISABLE 6 /* Indirect branch speculation permanently restricted */
#define TASK_PFA_TEST(name, func) \
static inline bool task_##func(struct task_struct *p) \
@ -1484,6 +1486,13 @@ TASK_PFA_CLEAR(SPEC_SSB_DISABLE, spec_ssb_disable)
TASK_PFA_TEST(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
TASK_PFA_SET(SPEC_SSB_FORCE_DISABLE, spec_ssb_force_disable)
TASK_PFA_TEST(SPEC_IB_DISABLE, spec_ib_disable)
TASK_PFA_SET(SPEC_IB_DISABLE, spec_ib_disable)
TASK_PFA_CLEAR(SPEC_IB_DISABLE, spec_ib_disable)
TASK_PFA_TEST(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable)
TASK_PFA_SET(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable)
static inline void
current_restore_flags(unsigned long orig_flags, unsigned long flags)
{

1
include/uapi/linux/prctl.h
View File

@ -212,6 +212,7 @@ struct prctl_mm_map {
#define PR_SET_SPECULATION_CTRL 53
/* Speculation control variants */
# define PR_SPEC_STORE_BYPASS 0
# define PR_SPEC_INDIRECT_BRANCH 1
/* Return and control values for PR_SET/GET_SPECULATION_CTRL */
# define PR_SPEC_NOT_AFFECTED 0
# define PR_SPEC_PRCTL (1UL << 0)

1
tools/include/uapi/linux/prctl.h
View File

@ -212,6 +212,7 @@ struct prctl_mm_map {
#define PR_SET_SPECULATION_CTRL 53
/* Speculation control variants */
# define PR_SPEC_STORE_BYPASS 0
# define PR_SPEC_INDIRECT_BRANCH 1
/* Return and control values for PR_SET/GET_SPECULATION_CTRL */
# define PR_SPEC_NOT_AFFECTED 0
# define PR_SPEC_PRCTL (1UL << 0)