On Fri, May 10, 2024 at 04:29:19PM -0700, Charlie Jenkins wrote:
On Wed, Apr 03, 2024 at 04:35:05PM -0700, Deepak Gupta wrote:
Three architectures (x86, aarch64, riscv) have support for indirect branch
tracking feature in a very similar fashion. On a very high level, indirect
branch tracking is a CPU feature where CPU tracks branches which uses
memory operand to perform control transfer in program. As part of this
tracking on indirect branches, CPU goes in a state where it expects a
landing pad instr on target and if not found then CPU raises some fault
(architecture dependent)
x86 landing pad instr - `ENDBRANCH`
aarch64 landing pad instr - `BTI`
riscv landing instr - `lpad`
Given that three major arches have support for indirect branch tracking,
This patch makes `prctl` for indirect branch tracking arch agnostic.
To allow userspace to enable this feature for itself, following prtcls are
defined:
- PR_GET_INDIR_BR_LP_STATUS: Gets current configured status for indirect
branch tracking.
- PR_SET_INDIR_BR_LP_STATUS: Sets a configuration for indirect branch
tracking.
Following status options are allowed
- PR_INDIR_BR_LP_ENABLE: Enables indirect branch tracking on user
thread.
- PR_INDIR_BR_LP_DISABLE; Disables indirect branch tracking on user
thread.
- PR_LOCK_INDIR_BR_LP_STATUS: Locks configured status for indirect branch
tracking for user thread.
Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
---
include/uapi/linux/prctl.h | 27 +++++++++++++++++++++++++++
kernel/sys.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 57 insertions(+)
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 3c66ed8f46d8..b7a8212a068e 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -328,4 +328,31 @@ struct prctl_mm_map {
*/
#define PR_LOCK_SHADOW_STACK_STATUS 73
+/*
+ * Get the current indirect branch tracking configuration for the current
+ * thread, this will be the value configured via PR_SET_INDIR_BR_LP_STATUS.
+ */
+#define PR_GET_INDIR_BR_LP_STATUS 74
+
+/*
+ * Set the indirect branch tracking configuration. PR_INDIR_BR_LP_ENABLE will
+ * enable cpu feature for user thread, to track all indirect branches and ensure
+ * they land on arch defined landing pad instruction.
+ * x86 - If enabled, an indirect branch must land on `ENDBRANCH` instruction.
+ * arch64 - If enabled, an indirect branch must land on `BTI` instruction.
+ * riscv - If enabled, an indirect branch must land on `lpad` instruction.
+ * PR_INDIR_BR_LP_DISABLE will disable feature for user thread and indirect
+ * branches will no more be tracked by cpu to land on arch defined landing pad
+ * instruction.
+ */
+#define PR_SET_INDIR_BR_LP_STATUS 75
+# define PR_INDIR_BR_LP_ENABLE (1UL << 0)
+
+/*
+ * Prevent further changes to the specified indirect branch tracking
+ * configuration. All bits may be locked via this call, including
+ * undefined bits.
+ */
+#define PR_LOCK_INDIR_BR_LP_STATUS 76
+
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 242e9f147791..c770060c3f06 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2330,6 +2330,21 @@ int __weak arch_lock_shadow_stack_status(struct task_struct *t, unsigned long st
return -EINVAL;
}
+int __weak arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
+{
+ return -EINVAL;
+}
+
+int __weak arch_set_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
+{
+ return -EINVAL;
+}
+
+int __weak arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
+{
+ return -EINVAL;
+}
+
These weak references each cause a warning:
kernel/sys.c:2333:12: warning: no previous prototype for 'arch_get_indir_br_lp_status' [-Wmissing-prototypes]
2333 | int __weak arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
kernel/sys.c:2338:12: warning: no previous prototype for 'arch_set_indir_br_lp_status' [-Wmissing-prototypes]
2338 | int __weak arch_set_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~
kernel/sys.c:2343:12: warning: no previous prototype for 'arch_lock_indir_br_lp_status' [-Wmissing-prototypes]
2343 | int __weak arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
Can the definitions be added to include/linux/mm.h alongside the
*_shadow_stack_status() definitions?
Noted. Will work on a fix for this.
- Charlie
#define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
#ifdef CONFIG_ANON_VMA_NAME
@@ -2787,6 +2802,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
return -EINVAL;
error = arch_lock_shadow_stack_status(me, arg2);
break;
+ case PR_GET_INDIR_BR_LP_STATUS:
+ if (arg3 || arg4 || arg5)
+ return -EINVAL;
+ error = arch_get_indir_br_lp_status(me, (unsigned long __user *) arg2);
+ break;
+ case PR_SET_INDIR_BR_LP_STATUS:
+ if (arg3 || arg4 || arg5)
+ return -EINVAL;
+ error = arch_set_indir_br_lp_status(me, (unsigned long __user *) arg2);
+ break;
+ case PR_LOCK_INDIR_BR_LP_STATUS:
+ if (arg3 || arg4 || arg5)
+ return -EINVAL;
+ error = arch_lock_indir_br_lp_status(me, (unsigned long __user *) arg2);
+ break;
default:
error = -EINVAL;
break;
--
2.43.2
